Let's learn about collection and How to print Objects

Arrays

• My first question is can we add, remove value in array ? NO, we can add or remove a value from a array, we cannot manipulate because array is fixed size so we need to create another array to add or remove a value

    void pushValueArray(){
        int [] arr = {1,2,3,4};
        int [] arrCopy = new int[5];

        int i = 0 ;
        while(i<arr.length){
            arrCopy[i]=arr[i];
            i++;
        }
        arrCopy[arr.length]=5;
        System.out.println(Arrays.toString(arrCopy));
    }

---

• Can we replace a value in array? YES,array is fixed but we can change the values in that array by accessing their index like this

    void replaceValueInArray(){
        int[] arr = {10, 20, 30};
        arr[2]= 40;
        System.out.println(Arrays.toString(arr));
    }

• Can we print a Object? this is a tricky one ,

1. String is object
2. array is object
3. Object(new) is object

---

1. String is object

we can print String using System.out.println()

String str = "helllo";
System.out.println(str);

String is object so the referece address of the String should print but the Output will be helllo,why ?

Because String calls toString() method automatically,

public String toString(String x) {
    return this;
}

this happens in the behind the screens

---

2. array is object

we can print a Array? Yes we can!

int [] arr = {1,2,3,4};
System.out.println(arr); // ref address
System.out.println(Arrays.toString(arr)); // o/p : [1,2,3,4]

• Is the output is array or string? The output is String but in array Format because the array is object we cant print directly so we use Arrays.toString()

---

3. Object(new) is object(TBD)

can we print Object? Yes but we need to override it

class ClassName {
    int x = 10;

    @Override //TBD
    public String toString() {
        return "x = " + x;
    }

public static void main(String[] args){
ClassName obj = new ClassName();
System.out.println(obj); // o/p : x = 10
    }
}

---

What is auto boxing and auto unboxing ?

*1. Auto Boxing *
Autoboxing = converting primitive → object automatically

int x = 10;
Integer obj = x; // autoboxing

2. Auto Unboxing
Unboxing = converting object → primitive automatically

Integer obj = 10;
int x = obj; // unboxing

---