its all pass by reference. nothing is passed by value in Java unless
its a primitive datatype, such as int.

Be careful.

If you do not intend to alter the variable which was passed, make a
copy of it.

class test
{
public void swap(int x,int y)
{
int temp;
temp=x;
x=y;
y=temp;
}

public static void main(String args[])
{
test t1=new test();
int a=10;
int b=20;
t1.sawp(a,b);
System.out.print(a);//will not change print 10
System.out.print(b);//will not change print 20
}