• Declaring Array
  • Creating an Array
  • Printing out an Array
  • Popcorn Hack 1(Time 0.5 minute)
  • Array with custom Objects
  • Accessing Array Elements
  • Popcorn Hack #2(Time 1.5 Minutes)
  • Array Length
  • Modifying Array Elements
  • Iterating Through an Array

    • 6.1 Array Creation and Access

    MUST KNOW TERMS

    • Array: A data structure that holds a group of object references.
    • Element: A single item stored inside an array.
    • Element index: The location of an element in the array (in Java AND PYTHON(called a list) the first element is at index 0).
    • Array length: Number of elements in the Array

    Declaring Array

    To declare an array, you need the name of the array and the datatype.

    Syntax: dataType[] arrayName;

    (note in python that no need to declare which is called dynamic typing)

    int[] grades; // Declare an integer array
String[] class_list; // Declare a string array
boolean[] light_switch;

    Creating an Array

    Gives memory for the array but we need to specify its size for java compared to python(with arraylists in the next lesson you won’t)

    
// Syntax: arrayName = new dataType[size];
int[]grades = new int[5]; // Create an integer array with 5 elements
String[]class_list = new String[3]; // Create a string array with 3 elements
boolean[]light_switch= new boolean[5];

// Can also predefine the terms rather than setting to default value
int[]grades={100,90,100,10,20};
boolean[]light_switch={true,false,true,false,true};



    numbers=list()
names=list()
light_switch=list()

    Printing out an Array

    import java.util.Arrays;
// Printing out the array with java method
int[]grades={100,90,100,10,20};
System.out.println(Arrays.toString(grades));

    [100, 90, 100, 10, 20]

    Popcorn Hack 1(Time 0.5 minute)

    Create an array that represents numerous car brands(Audi, toyota,etc. )

    import java.util.Arrays;
String[]carbrands = {"Lamborghini", "Mercedes","BMW","Ferrari","Batmobile"};
System.out.println(Arrays.toString(carbrands));

    [Lamborghini, Mercedes, BMW, Ferrari, Batmobile]

    Array with custom Objects

    class Coder{
    public boolean codecodecoder;
    public int age;
    Coder(boolean codecodecoder, int age){
        this.codecodecoder=codecodecoder;
        this.age=age;
    }
    
}
Coder[]allthecoders=new Coder[5];


for(int i=0;i<allthecoders.length;i++){
    allthecoders[i]=new Coder(true,10);
}

System.out.println(Arrays.toString(allthecoders));

    [REPL.$JShell$26$Coder@5a4be8a2, REPL.$JShell$26$Coder@548c1d9b, REPL.$JShell$26$Coder@50b383d2, REPL.$JShell$26$Coder@15b117a0, REPL.$JShell$26$Coder@10baf34c]

    Accessing Array Elements

    Acsessing an element’s value using it’s index in the array

    int[] grades = {10, 20, 30, 40, 50};
int element = grades[1]; // Access the second grade (20) using index 2
System.out.println(element); // Output: 30

    20

    # Python translation/example
grades=[10,20,30,40,50]
student1_grade=grades[0] # the first element in the array/list
print(student1_grade)


    10

    Popcorn Hack #2(Time 1.5 Minutes)

    1. Make an array of chars, representing people’s grades
    2. Try to adjust the letter grade of at least 3 people
    private static void printGrades(char[] grades) {
    for (char grade : grades) {
        System.out.print(grade + " ");
    }
    System.out.println();
 }
 
 
 char[] grades = {'F', 'F', 'A', 'A'};
 System.out.println("original grades are: ");
 printGrades(grades);
 
 
 grades[0] = 'A'; 
 grades[1] = 'A'; 
 grades[2] = 'F';
 grades[3] = 'F';
 System.out.println("updates grades: ");
 printGrades(grades); 

    original grades are: 
F F A A 
updates grades: 
A A F F

    Array Length

    Finding the length of the array.

    int[] Students_commits = {10, 20, 30, 40, 50, 60, 70, 80, 90}; //number of commits for each student
int length = Students_commits.length; // Get the length of the array and assign to an integer variable
System.out.println("Array length and number of coders: " + length); // Output: Array length: 5

    Array length and number of coders: 9

    grades=[10,20,30,40,50,60,70,80,90]
length=len(grades)
print("number of students",length)

    number of students 9

    Modifying Array Elements

    Updates the value of a specific element in the array.

    // integer array

int[] grades = {10, 20, 30, 40, 50};
System.out.println("Before: "+Arrays.toString(grades));
grades[2] = 35; // Change the third grade to 35
System.out.println("After: "+Arrays.toString(grades));


// boolean array

boolean[]light_switch={true,false,true,false}; //array of light switches with true meaning the light is on and false meaning its off
System.out.println("Before: "+Arrays.toString(light_switch));
light_switch[0]=false; // turn off the first switch    true-->false
System.out.println("After: "+Arrays.toString(light_switch));

// String array
String[]student_names={"Bob", "Sir Mort"," Sir Tarun", "Sensei Wu"};
System.out.println("Before: "+Arrays.toString(student_names));
student_names[0]="Sir Jonathon";
System.out.println("After: "+Arrays.toString(student_names));



    Before: [10, 20, 30, 40, 50]
After: [10, 20, 35, 40, 50]
Before: [true, false, true, false]
After: [false, false, true, false]
Before: [Bob, Sir Mort,  Sir Tarun, Sensei Wu]
After: [Sir Jonathon, Sir Mort,  Sir Tarun, Sensei Wu]

    
# Python translation/example
grades=[10,20,30,40]
print("Before",grades)

grades[1]=100 # changing the secon d element to 100
print("After",grades)

    Before [10, 20, 30, 40]
After [10, 100, 30, 40]

    Iterating Through an Array

    Loops through the array, printing each element.

    int[] numbers = {10, 20, 30, 40, 50};
for (int i = 0; i < numbers.length; i++) { // going from the first index(0) to the last index(length of array-1)
    System.out.println("Index "+i+": "+numbers[i]);
}

    Index 0: 10
Index 1: 20
Index 2: 30
Index 3: 40
Index 4: 50

    numbers=[10,20,30,40]
for i in range(0,len(numbers)):
    print("Index",i,":",numbers[i])

    Index 0 : 10
Index 1 : 20
Index 2 : 30
Index 3 : 40