Java is Pass-By-Value

 

 

Primitive types swap method will never work because Java is strictly Pass-By-Value.

If you want to swap two arguments, use array or object to send reference as a value.

 

 

Example I

primitive types are never changed

class Main {
    //primitive type doesn't swap
    public static void swap(int i, int j)
    {
        int temp = i;
        i = j;
        j = temp;
    }
    public static void main(String[] args)
    {
        int i = 10;
        int j = 20;
        swap(i, j);
        System.out.println("i = " + i + ", j = " + j);
    }
}
 
//i = 10, j = 20

 

 

 

 

Example II

Reference types (Object, Array) are changed as they pass the reference as a value.

public class Main {
    public static void main(String[] args) {
        int arr[] = {3, 2};
 
        passByValue(arr);
        printArray(arr);
    }
 
    private static void passByValue(int[] arr) {
        swap(arr, arr[0], arr[1]);
    }
 
    private static void swap(int[] arr, int source, int target) {
        int tmp = arr[0];
        arr[0] = arr[1];
        arr[1] = tmp;
    }
 
    private static void printArray(int[] arr) {
        for (int data : arr) {
            System.out.print(data + ", "); //2, 3
        }
    }

class Test
{
    int x;
    Test(int i) { x = i; }
}
class Main
{
    public static void main(String[] args)
    {
        Test t = new Test(5);
 
        change(t);
        System.out.println(t.x);
    }
 
    public static void change(Test t)
    {
        t = new Test(0); //referred to other address so that it won't change the value
        t.x = 10;
    }
}