Passing values to methods in Java-Primitives and Objects

In this post we will discuss about how method calling ,value passing happens in Java.

1.Passing Object reference variables to a method :-

• when we pass an object to a method we are not actually passing object itself, we are passing object reference
• Reference variable holds the address location of object and a way to load into memory
• We are not passing actual reference variable,but a copy of reference variable-which holds the copy of bits present in actual value

Lets see below code snippent

Employee emp1=new Employee();

method1(emp1);

void method1(Employee emp)

{

}

Here both emp1 and emp point to same Employee Object in heap.

Example1 :-

public class ObjectReference {

private int var1;

private int var2;

public ObjectReference(int x, int y) {

var1 = x;

var2 = y;

}

public static void main(String[] args) {

ObjectReference op = new ObjectReference(5, 10);

System.out.println("before modify " + op.var1 + "&&" + op.var2);

op.modify(op);

System.out.println("after modify " + op.var1 + "&&" + op.var2);

}

void modify(ObjectReference pop) {

pop.var1 = pop.var1 + 10;

pop.var2 = pop.var2 + 10;

System.out.println("in modify " + pop.var1 + "&&" + pop.var2);

}

}

Output :-

before modify 5&&10

in modify 15&&20

after modify 15&&20

Here both op and pop reference variables are referring to same ObjectReference object .If one reference variable tries to change the value autotically it gets reflected to another varaible.

In the above example in change method we changed the value of var1 and var2 and when we print the value in main method it got reflected.

Now lets see what happens in case of primitive data types.

2.Passing primitive variables to a method :-

When we are passing primitive values to a method we are actually passing copy of bits that represent a value.Suppose we have int a=5,when we pass a to a method we are actually passing copy of bits of value 5. For this we use a terminology passbyvalue rather its passbycopyofvalue .

Example :-

public class PrimitivePass {

int a = 10;

public static void main(String[] args) {

PrimitivePass pp = new PrimitivePass();

System.out.println("Before change" + pp.a);

pp.change(pp.a);

System.out.println("After change" + pp.a);

}

void change(int pNum) {

pNum = pNum + 10;

System.out.println("in change" + pNum);

}

}

output :-

Before change10

in change20

After change10

From the output we can observe that value of a is not changed ,but in previous case we observed for object references the value has changed.

Note :-

• While passing an Object we actually pass copy of the object reference
• While passing a primitive type we pass the bits value stored in that variable
• In both the cases we send copy of bits,in primitives actual value is stored but in case of Object reference it stores the address of the object

Happy Learning

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