Call by reference and Call by value

Java uses call by value. That means all parameters to methods are pass by value or call by value,the method gets a copy of all parameter values and the method cannot modify the contents of any parameter variables that are passed to it.

Please see sample programs below.

call by value: 

class One

{

void display(int i,int j)

{

i*=4;

j/=4;

}  

}

class Two

{

public static void main(String as[])

{

int a=10;

int b=20;

System.out.println("before calling");

System.out.println("a="+a);

System.out.println("b="+b);

One sample=new One();

sample.display(a,b);

System.out.println("after calling");

System.out.println("a="+a);

System.out.println("b="+b);

}

}

OUTPUT:

before calling

a=10

b=20

after calling

a=10

b=20

call by reference:

class One

{

int a,b;

One(int i,int j)

{

a=i;

b=j;

}

void display(One ab) //pass an object

{

ab.a*=2;

ab.b/=2;

}

}

class Two

{

public static void main(String as[])

{

One sample=new One(10,20);

System.out.println("before calling");

System.out.println("a="+sample.a);

System.out.println("b="+sample.b);

sample.display(ab);

System.out.println("after calling");

System.out.println("a="+sample.a);

System.out.println("b="+sample.b);

}

}

Output:

before calling

a=10

b=20

after calling

a=20

b=10

By above example programs hope understood the difference between call by value and call by reference.