Java SE (Java Platform, Standard Edition)

class A
{
      int a,int b;
}
class B
{
       public static void main(String args[])
       {
                A ob = new A();
                ob.a = 10;
                ob.b = 20;
                System.out.println("Before swapping "+ob.a+" "+ob.b);
                swap(ob);
                System.out.println("After swapping "+ob.a+" "+ob.b);
       }
       public static void swap(A obj)
       {
                int temp = obj.a;
                obj.a = obj.b;
                obj.b = temp;
       }
}

tmp = a;
a = b;
b = tmp;

class A {

    int a;
    int b;

    public static void main(String[] args) {
        // obj is a reference that "points" to an instance of A
        A obj = new A();
        // The reference is passed, but it is passed by value because
        // the value of "obj" is copied.
        swap(obj);
        System.out.println(obj.a);
        System.out.println(obj.b);
    }

    static void swap(A arg) {
        // The variable "arg" is a reference that points to an instance of A
        // It's value has been copied from "obj" when it was passed in the
        // main method.  Modifying "arg" will not modify "obj".

        // This is not modifying "arg", it is dereferencing "arg" and modifying
        // the value of the variables "a" and "b" of the instance of A that "arg"
        // points to which would be the same as the instance "obj" points to.
        arg.a = 10;
        arg.b = 20;

        // This modifies the value of "arg" to point at a new instance of A
        // This would not affect "obj", they would now point at two different
        // objects
        arg = new A(); // Does not affect "obj"
        // This has no effect on "obj" because we're changing the values of
        // a and b on a different instance of A
        arg.a = 30;
        arg.b = 40;
    }

}

class Foo {
    String str_;
}

...

void m1(String str) {
    str = "abc";
}

void m2(Foo foo) {
    foo.str_ = "xyz";
}

String s = "ORIGINAL";
Foo f = new Foo();
foo.str_ = "ORIGINAL";

m1(s);
m2(f);


System.out.println(s); // prints "ORIGINAL"
System.out.println(f.str_); // prints "xyz"

// Objects are passed by reference

Class Test{
    int a,b;

......

// Objects are passed by reference>

main()
{
           int a=10,b=20;
           swap(a,b);
           printf("%d %d",a,b);
}
swap(int a,int b)
{
      int t=a;
      a=b;
      b=t;
}

main()
{
           int a=10,b=20;
           swap(&a,&b);
           printf("%d %d",a,b);
}
swap(int *a,int *b)
{
      int t=*a;
      *a=*b;
      *b=t;
}

swap(&a,&b);

swap(&a,&b);

void primPtrByVal(int* param1, int* param2) {
    int* tmp = param1;
    param1 = param2;
    param2 = tmp;
}

int i = 1;
int j = 2;
primPtrByVal(&i, &j);

void primByRef(int& param1, int& param2) {
    int tmp = param1;
    param1 = param2;
    param2 = tmp;
}

int i = 1;
int j = 2;
primByRef(i, j);