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892 lines
28 KiB
Markdown
892 lines
28 KiB
Markdown
# Computer Science Review Sheet
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> ## Exam Layout
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>> |Part|Description|Marks|
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>> |:---|:----------|:----|
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>> |```A```|**True / False**|10|
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>> |```B```|**Multiple Choice**<br>- All java code learnt, selection, loops, methods, Arrays, methods, strings|38|
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>> |```C```|**Short & Long Answers**<br>- Compare and contrast short code, methods, problem solving|20|
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>> |```Total```||68|
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## Unit 1: Intro To Programming
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> ```Comments```: are used to explain and clarify program ocde for human reader
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> |Operator|Uses|Description|
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> |:-------|:---|:----------|
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> |+|a + b|Addition|
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> |-|a- b|Subtraction|
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> |*|a * b|Multiplication|
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> |/|a / b|Division|
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> |%|a % b|Mod, the Remainder|
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> **BEDMAS** rules still apply
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> ## Strings
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>> **```String:```** means a group of many characters
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>> **```String Concatenation```**: means that two strings are combined into one using the "r" sign
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> ## Variables
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> - Holder for data
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> - We can use words instead of just a single letter
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> - can store more than just numbers
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> - a place in memory (RAM: random access memory) where it can be stored or referred to
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> - Name, type, value
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>> To declare a variable
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>> 1. Name
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>> 2. Data Type
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>> A variable is the name of a reserved memory location
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>> A varaible name is called an identifier
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>> Reserved words cannot be used as an identifier
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> ## Java Primitives
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> Variables can be created for any of the data types listed
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> The chart shows examples of how to create a new variable for each primitive
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> |Type|Range|Size|Variable|Declaration|
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> |:---|:----|:---|:-------|:----------|
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> |byte|-128 to 127|8 bits|bits_8|byte bits_8;|
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> |short|-32768 to 32767|16 bits|TALL|short TALL;|
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> |int|-2 billion to 2 billion|32-bits|sum|int sum;|
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> |long|-9 quintillion to 9 quintillion(huge)|64 bits|mile|long mile;|
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> |float|-3.4e<sup>+/-38</sup> to 3.4e<sup>+/-38</sup>|32 bits|pi|float pi;|
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> |double|-1.7e<sup>+/-308</sup> to 1.7<sup>+/-308</sup>|64 bits|stuff|double stuff;|
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> |char|Single (unicode) characters|16 bits|letter|char letter;|
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> ## Operations
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>> |Operation|Notation|Equivalent|Result Type|
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>> |:--------|:-------|:---------|:----------|
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>> |equals|a == b||boolean|
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>> |addition|a + b||number|
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>> |subtraction|a - b||number|
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>> |multiplication|a * b||number|
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>> |division|a / b||number|
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>> |less|a < b||boolean|
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>> |less or equal|a > b|a <= b||boolean|
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>> |more|a >= b|not (a < b)|boolean|
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>> |more or equal|a >= b|not(a == b)|boolean|
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>> |negation|-b|0 - b|number|
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> ## Sample Code
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>> ``` java
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>> class AddTip{
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>> public static void main(String[]args){
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>> double amount; // variable declaration,
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>> // can store a double(real number)
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>> // no value assigned to it yet
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>> // variable name is identifier
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>> double pi = 3.1415926;
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>> amount = 19.95; // variable amount has been assigned value of 19.95
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>> amount = amount + 3.00; // takes current vaue of amount(19.95) and add 3.00 to it
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>> // then assigns the new value to amount(22.95)
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>> System.out.print("We will pay $");
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>> System.out.print(amount);
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>> System.out.print(" for the pizza delivery");
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>> // prints amount
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>> }
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>> }
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>> ```
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> ## Java Data Types
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>> ### Java primitive types
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>>> boolean
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>>> number:
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>>> - integer
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>>> - byte
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>>> - short
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>>> - int
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>>> - long
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>>> - char
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>>> - floating-point
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>>> - float
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>>> - double
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>>> **Remember** ```String``` is not a primitive type
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>> ```equals(String)``` - Method compares the current string to another string and returns true if the two contain the same value, false if different
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>> ```substring(int, int)``` - takes two values - an int for the first character and an int for the last character (exclusive)
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- substring(1, 10) returns the substring from index 1 to index ```9```
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- returns that part of the string
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>> ### Strings
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>> - String - a set of individual characters
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>> - string start at zero - zero indexing
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>> - an array of characters
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>> - Char(acter) - hold the same type of information as a string - but only one character
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>> - use single quotes rather than double quotes
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>> - many different methods that can be used with char
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>> - uses less memory than a string
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>>> ```java
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>>> String name = "Ms Andrighetti";
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>>> String firstThree, lastEleven;
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>>> firstThree = name.substring(0, 3);
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>>> lastEleven = name.substring(4, 15);
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>>> System.out.println(firstThree);
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>>> System.out.println(lastEleven);
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>>> ```
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>> - first character is index 0 because zero-indexed
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>> - substring specifies the first characters you want and the last character you don't want
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>> - if you try to access a point beyond the end of the String, you will get an error
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>> - ```length()``` - tells you how many character are in a string
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>> - length gives you the length of string not last index of the string
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>>> ```java
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>>> String word = "Hello";
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>>> int length = word.length();
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>>> System.out.println(length);
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>>> ```
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>> ### Boolean Expressions
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>> - can only have 2 possible value(true or false)
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>> - compare must be compatible type
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>>> |Symbol|Meaning|
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>>> |:-----|:------|
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>>> |==|equal to|
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>>> |!=|not equal to|
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>>> |>|greater than|
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>>> |<|less than|
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>>> |>=|greater than or equal to|
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>>> |<=|less than or equal to|
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>> ```Modulus operator (%)```: returns the remainder of 2 numbers
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>> ```String```: stores characters / text
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>> ```String comparison```: different from primitive type comparison
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>> - cannot use ```==``` sign
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>> - use boolean expression ```object1.equals(object2)```
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> ## Reading Input (Scanner Class)
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>> ```import``` scanner class to use it
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>> use
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>> ```java
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>> import java.util.Scanner;
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>> ```
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> - to tell compiler to include scanner class in the .class file
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> - line at very top of file
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> - create scanner using
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>> ```java
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>> Scanner myScanner = new Scanner(System.in);
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>> ```
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>> |To read this...|...Make this method call|
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>> |:--------------|:-----------------------|
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>> |a number with no decimal point in it|nextInt()|
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>> |a number with a decimal point in it|nextDouble()|
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>> |a word(ending in a blank space, for example)|next()|
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>> |a line(or what remains of a line after you've already read some data from the line)|nextLine()|
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>> |a single character(such as a letter, a digit or a punctuation character|next.charAt(0)|
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> ## Output
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> - using standard output system:
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>> ```java
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>> System.out.println()
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>> ```
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> - this outputs to the console
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> ## Selection statements
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> - allow java to make a decision
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> - depending on decision, program will function differently each time it is run
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>> ```java
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>> if(condition){
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>> //then perform some commands
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>> // outcome
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>> }
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>>```
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>> ### Example:
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>>> ```java
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>>> int age = 17;
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>>> if(age >= 16){
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>>> // execute if condition
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>>> System.out.println("You are " + age);
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>>> System.out.println("You can learn to drive");
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>>> } // skips if condition not met
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>>>```
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>> ### ```=``` vs ```==```
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>> - ```=```: assignment
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>> - ```==```: comparison
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>> ### if.... else if.... else
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>>> ```java
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>>> if(condition){
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>>> statement1;
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>>> } else{
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>>> statement2;
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>>> // -----------------------
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>>> }
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>>> if(num > 10){
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>>> System.out.println("Your number is greater than 10");
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>>> } else{
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>>> System.out.println("Your number is less than or equal to 10");
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>>> }
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>>> ```
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>> - used when program needs to choose from a variety of situations
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>> - use else if to specify another condition
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>> - helps to control the flow of your program
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>> - helps make decision when 3 or more conditions must be considered
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>> - makes program more efficient
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>>> ```java
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>>> if(age >= 16){
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>>> System.out.println("You can drive");
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>>> }else if(age == 15){
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>>> System.out.println("You can drive next year");
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>>> }
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>>> ```
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>>> - else if statement is additonal part of if statement
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>>> - can be multiple else if statement in a single if construct
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>>> - one if statement can only run one outcome
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>> else - used to specify outcome that will be run if one other conditions are met
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>> debugging - the process of finding out and correcting erros in a program
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> ## Types of Errors
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>> ```Compile-Time-Errors``` - Complier checks syntax
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>> - syntax error - how you write your statements(your grammar)
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>> - Spelling mistakes
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>> - Punctuation errors
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>> - Missing brackets, curly brackets, key words
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>> - Incompatible types of data
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>> - .class file not created
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>> ```Logical Error``` - Hardest to detect/solve
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>> - compiles and runs correctly but incorrect results
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>> - wrong formula
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>> - wrong approach taken
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>> ```Run-time Error``` - occur during program execution
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>> - causes program to terminate abnnormally
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>> - try dividing by zero
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> ## Logical Statements
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>> True/False
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>> 3 basic logical operator
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>> ```OR/AND/NOT```
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>> **```AND```**: when all values are true
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>> **```OR```**: when at least one value is true
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>> **```NOT```**: flips the value of a statement
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>> ### Truth Table
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>> - Used to study logic by computer scientists
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>>> | X | Y |X OR Y|X AND Y|
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>>> |:--|:--|:-----|:------|
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>>> |T|T|T|T|
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>>> |T|F|T|F|
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>>> |F|T|T|F|
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>>> |F|F|F|F|
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>> operator precendence - evaluate left to right
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>> 1. AND( & & ) - checks first statement, if it is true, check the second one
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>> 2. OR( | | ) - checks the first statement and second statement
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>> 3. NOT( ! ) - reverses the statement
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> ## Loops
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>> Allows coders to repeat code
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>> Exit condition in loop
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>> ```java
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>> while(condition){
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>> // do something
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>> }
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>> ```
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>> ### While Loops
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>> - consists of a condition statement that are executed while the condition is true
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>> - types of conditions used in a while statement are the same as in the ```if statement```
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>> - while the condition is true, repeat the statements in the loop
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>>> ```java
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>>> while(num <= 10){
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>>> System.out.println("Enter a number higher than 10.");
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>>> num = scan.nextInt();
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>>> }
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>>> ```
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>> - the program continues repeating until the num is greater than 10
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>> - there may be times when you may want to specify more than one condition
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>> - no limit to the number of conditions, but should limit to 2 or 3
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>> - can combine conditions(logical statements) using ```&&``` and ```||``` conditional operators
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>>> ```java
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>>> while(num >= 1 && num <= 10){ // runs until num is between 1 and 10
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>>> num = myScanner.nextInt();
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>>> }
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>>> ```
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>> Incrementing By One
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>> ``` java
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>> mynumber = mynumber + 1;
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>> // is the same as:
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>> mynumber += 1;
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>> // is the same as:
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>> mynumber++;
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>>
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>> ```
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>> Why counter: To keep track of how many times a loop has executed
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>> ```java
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>> int counter = 0;
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>> int guess = 0;
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>> while(guess != 7){
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>> System.out.println("Guess a number between 1 and 10");
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>> guess = scan.nextInt();
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>> counter++;
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>> }
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>> System.out.println("It took you " + counter + " tries!");
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>> ```
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>> ### For Loops
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>> - include three distinct statements separated by semicolon
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>> - first statement declares the counter variable
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>> - second statement specifies exit condition
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>> - third statement increments the counter variable after each iteration of the loop
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>> - counter variable only exists within loop
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>>> ```while``` and ```for``` loop: - may not need to run if condition is false
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>>> ```java
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>>> for(int i = 0; i < 10; i++){ // this loop runs 10 times
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>>> // do stuff here
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>>> }
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>>> ```
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>> ### Accumulator
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>> - variables that add any value to a sum or total
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>> - realize the need for the variable
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>> - declare the variable
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>> - initialize it (give it a start value, usually 0)
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>> - accumulate the value in a loop (add the value to the variable)
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>> ### Do while Loop
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>>> They must run minimum once
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>>> After running once, it checks the continue condition at the end of the iteration
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>>> ```java
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>>> do {
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>>> // do stuff here
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>>> }while(condition);
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>>> ```
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>>> Example
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>>> ```java
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>>> public static void main(String[]args){
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>>> Scanner sc = new Scanner(System.in);
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>>> int total = 0, value;
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>>> do {
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>>> System.out.println("Enter values to sum and 0 to quit");
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>>> value = input.nextInt();
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>>> total = total + value;
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>>> }while(value != 0);
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>>> System.out.println("Your total is: " + total);
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>>> }
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>>> ```
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> ### Random Number Generation
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>> ### Method 1
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>> ```java
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>> import java.util.Random;
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>> public class {
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>> public static void main(String[]args){
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>> Random randGen = new Random();
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>> int randNumber = randGen.nextInt(100) + 1;
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>> }
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>> }
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>> ```
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>> ### Method 2
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>> using Math class
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>> ```java
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>> int myRandNumber = (int) (Math.random() * 100) + 1;
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>> ```
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# Unit 2: Arrays
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> ```Arrays```: a data structure that allow you to hold multiple pieces of data, in a single object
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> - hold a predetermined number of elements
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> - must be same type
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> ``` java
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> int, String, char, boolean, double, complex types
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> ```
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> - [] - square brackets means index
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> - arrays always start at 0 index
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> - must be assigned a fixed size
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> - use counted loop with array to do things
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> ## Example:
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>> ```java
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>> // declare an array of 5 integer
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>> int [] numArray = new int[5];
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>> // set the 0 index of numArray to 123
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>> numArray[0] = 123;
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>> // get the array size
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>> int arraySize = numArray.length;
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>> ```
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> ### Mid - program initialization of arrays
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> - can declare the array at the beginning ant set size
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> - All variable and arrays must be declared at the beginning of the program for proper conventions
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>> ```java
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>> // declare variables and array
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>> String[] names;
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>> int numValues;
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>> System.out.println("How many names?");
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>> numValues = scan.nextInt();
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>> // initialize array
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>> names = new String[numValues];
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>> ```
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> ## Display
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> - Simply iterate throughout the array and just print out all the elements
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> - A ```for``` loop or ```while``` loop can be used
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> - Simple display code
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>> ```java
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>> System.out.print("The elements in the array are: ");
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>> for(int i = 0; i < array.length; i++){
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>> System.out.print(array[i] + " ");
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>> }
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>> System.out.println();
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>> ```
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> ## Search
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> - To iterate through in array, or to search an element
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> - Just loop through the array until you find the element
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> - Use ```length``` to iterate through the entire array
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> - Use appropriate comparators like ```==``` and ```.equals()```
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> - Simple search code
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>> ```java
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>> int element = 12;
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>> for(int i = 0; i < array.length; i++){
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>> if(array[i] == element){
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>> System.out.println("Element found at index: " + i);
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>> break;
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>> }
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>> }
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>> ```
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> ## Finding The Average
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> - Sum all the elements of the list and divide by the number of elements
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> - Simple average finding code
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>> ```java
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>> int sum = 0;
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>> for(int i = 0; i < array.length; i++){
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>> sum += array[i];
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>> }
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>> double average = sum / array.length;
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>> System.out.println("The average is: " + average);
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>> ```
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> ## Finding Min / Max
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>> ### Finding the Min
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>> - Algorithm
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>>> ```
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>>> set the min to the first element, we assume its the minimum
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>>> go through each element in the array, if we find an element that is smaller than the current min
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>>> change the current min to it, we can use either Math.min() or the < operator
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>>> after iterating through the entire list, the min will be the smallest number
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>>> ```
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>> - Code
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>>> ```java
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>>> int min = array[0];
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>>> for(int i = 0; i < array.length; i++){
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>>> if(array[i] < min){
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>>> min = array[i];
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>>> }
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>>> }
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>>> System.out.println("Smallest value is: " + min);
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>>> ```
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>> ### Finding the Max
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>> - Algortihm
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>>> ```
|
|
>>> set the max to the first element, we assume its the maximum
|
|
>>> go through each element in the array, if we find an element that is bigger than the current max
|
|
>>> change the current max to it, we can use either 'Math.max()' or the '>' operator
|
|
>>> after iterating through the entire list, the min will be the biggest number
|
|
>>> ```
|
|
|
|
>> - Code
|
|
>>> ```java
|
|
>>> int max = array[0];
|
|
>>> for(int i = 0; i < array.length; i++){
|
|
>>> if(array[i] > max){
|
|
>>> max = array[i];
|
|
>>> }
|
|
>>> }
|
|
>>> System.out.println("Biggest value is: " + max);
|
|
>>> ```
|
|
|
|
# Unit 3: Sorting
|
|
- ```sorting```: the process of arranging a list of items into a well-defined order
|
|
- final list rearrangement of the original list
|
|
|
|
> ## Bubble Sort
|
|
> - when x numbers in array, loop x - 1 times
|
|
> - The bubble sort algorithm works by swapping adjacent pairs in the list until all adjacent pairs are sorted in order, at which the entire list is sorted
|
|
> - by making passes through the array, each pass moves from left to right
|
|
> - the first pass compares element 1 and element 2 and swaps them if they are out of order, then compares element 2 and element 3 and swaps them if they are out of order, and so on
|
|
> - the largest element is moved to the right
|
|
> - for a length of n, there are n - 1 passes
|
|
|
|
>> |Pass 1|Pass 2|Pass 3|Pass 4|
|
|
>> |:-----|:-----|:-----|:-----|
|
|
>> |```3 6``` 5 4 2|```3 5``` 4 2 6|```3 4``` 2 5 6|```3 2``` 4 5 6|
|
|
>> |3 ```6 5``` 4 2|3 ```5 4``` 2 6|3 ```4 2``` 5 6|2 3 4 5 6|
|
|
>> |3 5 ```6 4``` 2|3 4 ```5 2``` 6|3 2 4 5 6|
|
|
>> |3 5 4 ```6 2```|3 4 2 5 6|
|
|
>> |3 5 4 2 6|
|
|
|
|
>> |Number of Elements|Number of Passes|Number of Comparisons|
|
|
>> |:-----------------|:---------------|:--------------------|
|
|
>> |4|3|6|
|
|
>> |5|4|10|
|
|
>> |6|5|15|
|
|
>> |7|6|21|
|
|
>> |8|7|28|
|
|
>> |9|8|36|
|
|
>> |10|9|45|
|
|
>> |```n```|```n - 1```|```n * (n - 1) / 2```|
|
|
|
|
> ## Algorithm
|
|
|
|
>> ```
|
|
>> repeat the following n -1 times
|
|
>> for each element in the array, starting at the first element
|
|
>> compare items in current positions with the element in the next position
|
|
>> if item in current position is greater than item in next position then
|
|
>> swap the 2 items using the following steps
|
|
>> temp = current list item
|
|
>> current list item = next list item
|
|
>> next list item = temp
|
|
>> ```
|
|
|
|
> ## Code
|
|
|
|
>> ```java
|
|
>> // array called list
|
|
>> for (int i = 0; i < list.length - 1; i++){
|
|
>> for(int j = 0; j < list.length - 1 - i; j++){
|
|
>> if(list[j] > list[j + 1]){
|
|
>> int temp = list[j];
|
|
>> list[j] = list[j + 1];
|
|
>> list[j + 1] = temp;
|
|
>> }
|
|
>> }
|
|
>> }
|
|
>> ```
|
|
|
|
> ```CompareTo(String)```
|
|
> - result is a ```negative integer``` if this String object lexicographically(alphabetically) precedes the argument string
|
|
> - result is a ```positive integer``` if this string object
|
|
> - result is ```zero``` if the string are equal
|
|
|
|
# Unit 4: Methods
|
|
> ```methods``` - subprograms in java
|
|
> - a group of programming statements that are given a name
|
|
> two types of methods
|
|
> - ```function-type methods``` - calculates and returns a value
|
|
> - ```procedure-type methods``` - executes some commands and has a void return type
|
|
|
|
> ## Why Methods
|
|
> - allows for code to be reused throughout a program
|
|
> - more efficient and neatly organized programs
|
|
> - allow for easy modification later on
|
|
|
|
> ## Examples:
|
|
>> ```java
|
|
>> public static int square(int number){
|
|
>> return number * number;
|
|
>> }
|
|
>>
|
|
>> public static void printHelloWorld(){
|
|
>> System.out.println("Hello World!");
|
|
>> }
|
|
>> ```
|
|
|
|
>> int - return - type
|
|
>> square - method name
|
|
>> int number - formal parameter
|
|
|
|
> ## Built in methods
|
|
|
|
>> |Method|Description|
|
|
>> |:-----|:----------|
|
|
>> |```Math.abs(x)```| returns the absolute value of the paramter x|
|
|
>> |```Math.random()```|returns a pseudorandom value uniformally distributed between 0 and 1|
|
|
>> |```Math.round(x)```|returns the value of x rounded according to the usual arithmetic rules|
|
|
>> |```Math.ceil(x)```|returns the value of x rounded up to the nearest integer|
|
|
>> |```Math.floor(x)```|returns the value of x rounded down to the nearest integer|
|
|
>> |```Math.max(x, y)```|returns the greatest of values x and y|
|
|
>> |```Math.min(x, y)```|returns the smallest of values x and y|
|
|
>> |```Math.sqrt(x)```|returns the value of the square root of x|
|
|
>> |```Math.pow(x, y)```|returns the value if x raised to the power of y|
|
|
>> |```Math.PI```|returns the double value of the mathemetical π|
|
|
>> |```.charAt(x)```|returns the character at index x|
|
|
>> |```.substring(st, ed)```|returns the string beginning at st and ending at ed(exclusive)|
|
|
>> |```.toLower()```|returns the lower-cased version of the string|
|
|
>> |```.toUpper()```|returns the upper-cased version of the string|
|
|
>> |```.split(regex)```|splits the string at index(s) where the ```regex``` appears and returns an array of strings|
|
|
>> |```isCharacter(x)```|checks if x is an character|
|
|
|
|
> ## More on Methods
|
|
>> - ```signature``` - method name and parameter
|
|
>> - if method is to be used outside the class in which it is defined, it must be declared as a public in the class
|
|
>> - call or invoke a method to use it
|
|
>> - ```formal parameter``` - the names of the parameter accepted in the signature
|
|
>> - ```actual parameter``` - the values passed into a method
|
|
>> - if no parameters, empty set of parentheses are used
|
|
>> - ```java
|
|
>> c.readInt();
|
|
>> ```
|
|
|
|
> ## Return Type Methods
|
|
> - public static ```return type``` ```method name```(parameters)
|
|
> - Example:
|
|
>> ```java
|
|
>> public static int square(int num1){
|
|
>> // do stuff here
|
|
>> }
|
|
>> ```
|
|
|
|
> ## Void Type Methods
|
|
> - public static void ```method name```(parameters)
|
|
> - Example:
|
|
>> ```java
|
|
>> public static void drawPicture(){
|
|
>> // do stuff here
|
|
>> }
|
|
>>
|
|
>> public static void draw4Circles(int x1, int y1, int x2, int y2){
|
|
>> // do stuff here
|
|
>> }
|
|
>> ```
|
|
|
|
> ## Java language - Strongly typed
|
|
> - meaning you are not allowed to assign a value to a variable that is consistent with its declare type
|
|
|
|
> ## ```Scope of variable``` - the part of the program over which the variable can be accessed or referenced
|
|
> - referes to the ```accessibility``` of a variable
|
|
> - variables cannot be accessed before they are declared
|
|
|
|
> Variables can be declared in several different places
|
|
> - class bodies (referred to as global or class level variables)
|
|
> - as parameters to methods(in method signature)
|
|
> - in a method body
|
|
> - in a statement block (like a loop or a while loop)
|
|
|
|
>> ```java
|
|
>> public class VariableExample{
|
|
>> static Scanner myScanner = new Scanner(System.in);
|
|
>>
|
|
>> public static void main(String[]args){
|
|
>> // main method
|
|
>> }
|
|
>> }
|
|
>> ```
|
|
|
|
> - Description of Example
|
|
> - variable myScanner is declared outside of the main method in the class level
|
|
> - the variable is considered to be a global variable that can be accessed anywhere in the class
|
|
> - for now, global variables should have the keyword ```static``` preceding the declaration
|
|
|
|
> - In methods
|
|
> - a method may declare local variable in the body of the method for use onlyin that method
|
|
> - variable may also be declared in the parameter list - only can be accessed in the method
|
|
|
|
>> ```java
|
|
>> public static int thirdPower(double number){
|
|
>> int cube; // local variable
|
|
>> cube = number * number * number;
|
|
>> return cube;
|
|
>> }
|
|
>>
|
|
>> public static double thirdPower(double number){
|
|
>> double cube;
|
|
>> cube = number * number * number;
|
|
>> return cube;
|
|
>> }
|
|
>> ```
|
|
|
|
> - variable cube in thirdpower is local to that method
|
|
> - local variables cannot be accessed from outside of the method
|
|
|
|
> - In blocks of code
|
|
> - variables defined in a block are only accessible from within the block
|
|
> - the scope of the variable is the block in which it is defined
|
|
|
|
>> ```java
|
|
>> for(int x = 0; x < 5; x++){
|
|
>> System.out.println(x);
|
|
>> }
|
|
>> ```
|
|
>> - the variable x can only be accessed in the for loop
|
|
|
|
> ## Method void return type
|
|
> - return type void means that a method will not return a value
|
|
> - the method can still have parameter when the return type is void
|
|
|
|
> ## Naming conventions
|
|
> - method names should indicate an action
|
|
> - verbs make good methods names
|
|
> - methods names should begin with a lowercase letter and then an uppercase letter should begin with each word within the name
|
|
> - method names may not contain spaces
|
|
|
|
> ## Pass By Value
|
|
|
|
>> ```java
|
|
>> public static void drawBar(int length){
|
|
>> for(int i = 0; i < length; i++){
|
|
>> System.out.print("* ");
|
|
>> }
|
|
>> System.out.println();
|
|
>> }
|
|
>> ```
|
|
|
|
> - means that when a method is called, a ```copy``` of the value of each argument is passed to the method
|
|
> - this copy can be changed inside the method, however such a change will have no effect on the actual argument
|
|
> - copies of the actual parameter values from main are sent to the methods, where they become ```foramal parameters```. When the method is finished, the copies are discarded. The actual ```paramter``` values remain unchanged. Notice that nothing is returned in the above method and how values ```a``` and ```b``` are not changed in the main method when passed in the method below
|
|
|
|
>> ```java
|
|
>> public static void main(String[]args){
|
|
>> int a = 0, b = 10;
|
|
>> System.out.println("The starting value of a and b are: " + a + " and " + b);
|
|
>> change(a, b);
|
|
>> System.out.println("The values of a and b are: " a + " and " + b);
|
|
>> }
|
|
>> public static void change(int a, int b){
|
|
>> a = 999;
|
|
>> b = 21;
|
|
>> }
|
|
>> ```
|
|
|
|
> ## Pass by reference
|
|
|
|
> - occurs when an object is passed to a method, its memory address location (its ```reference```) is used
|
|
> - ```Arrays``` behave like objects, their memory location is passed to the method
|
|
> - that means that when an array is manipulated in the method that we are actually ```changing``` the array
|
|
> - be cautious when sending an array in the method as it will change the data in the original array
|
|
|
|
>> ```java
|
|
>> public static void main(String[]args){
|
|
>> int array[] = new int[4];
|
|
>> a[0] = 1000;
|
|
>> a[1] = 2000;
|
|
>> a[2] = 3000;
|
|
>> a[3] = 4000;
|
|
>> System.out.print("The values of the array are: ");
|
|
>> for(int i = 0; i < a.length; i++){
|
|
>> System.out.print(a[i] + " ");
|
|
>> }
|
|
>> System.out.println();
|
|
>> System.out.println();
|
|
>>
|
|
>> change(array);
|
|
>>
|
|
>> System.out.print("The values of the array are: ");
|
|
>> for(int i = 0; i < a.lengh; i++){
|
|
>> System.out.print(a[i] + " ");
|
|
>> }
|
|
>> System.out.println();
|
|
>> }
|
|
>> public static void change(int array[]){
|
|
>> array[0] = 1;
|
|
>> array[1] = 2;
|
|
>> array[2] = 3;
|
|
>> array[3] = 4;
|
|
>> }
|
|
>> ```
|
|
|
|
# Unit 5: Software Design Process
|
|
|
|
> ## 5 Steps
|
|
|
|
>> |Step #|Description|
|
|
>> |:-----|:----------|
|
|
>> |Analysis|Also called ```problem solving```, its the process of ```breaking problems down into smaller more manageable parts```|
|
|
>> |Design|In this stage, an ```algorithm``` which is a set of instructions defined to solve the problem|
|
|
>> |Implementaion|Also referred to as ```coding```. Where you express the algorithm in a ```programming language```|
|
|
>> |Testing|Invlovles the running of the program will a full range of data. Valid data: ```the data the user should be inputting.``` Invalid data: ```incorrect or unexpected data```|
|
|
>> |Maintenance|```Maintaining a program over time so that any changes are needed are incorporated```|
|
|
|
|
> **```valid data```**: the data the user should be inputting
|
|
> **```invalid data```**: ```incorrect``` or ```unexpected``` data
|
|
> **```algorithm```**: a set of ```insturction``` defined to ```solve``` the problem
|
|
> **```Well designed program```**: a program that ```reliably``` solves the problem it was created to solve
|
|
> **```Waterfall Model```**: A flow chart, each phase must be completed before the next one
|
|
|
|
> ## Programmers
|
|
> - Programmers have the abilites to:
|
|
> - 1. Solve Problems
|
|
> - 2. Organize information
|
|
> - 3. Design Solutions
|
|
> - 4. Express instructions in a logical sequence
|
|
> - 5. Input them into a computer
|
|
|
|
> - My Points for abilities and characteristics:
|
|
> - 1. Communicate, collabration
|
|
> - 2. Present their solution
|
|
> - 3. Work as a team
|
|
|
|
# Unit 6: Problem Solving
|
|
|
|
> ## Code Correction
|
|
> - ```;``` semicolons
|
|
> - Accessing outside of specified range of a ```string``` or ```array```
|
|
> - Missing or extra brackets ```{}```, ```()```, ```[]```
|
|
> - Undeclared variables, scope of an variable
|
|
> - Wrong method calls
|
|
> - incorrect syntax
|
|
|
|
> ## Problem solving
|
|
> - **Debugging**
|
|
> - Printing out code
|
|
> - Rubber ducking your code
|
|
|
|
# Credits
|
|
> Creator, Editor: --> magicalsoup (ME)!
|
|
> Helper, Information Provider(s): --> Matthew Wong, Samantha Ouyang
|
|
|
|
|
|
|
|
|