Pass by Value and Pass by Reference in Java

Java is one of the most fundamental programming languages that anyone can pick up. It is so simple at the same time, the possibility of what you can develop using Java, is infinite! This is what makes Java the most widely used language in the industry today. This blog will help you understand about the pass by value and the pass by reference in Java in the following sequence:

• Pass by Value and Pass by Reference in Java
• Illustration with Program

Pass by Value and Pass by Reference in Java

Pass by Value and Pass by reference is the two ways by which we can pass a value to the variable in a function.

• Pass by Value: It is a process in which the function parameter values are copied to another variable and instead this object copied is passed. This is known as call by Value.

• Pass by Reference: It is a process in which the actual copy of reference is passed to the function. This is called by Reference.

Talking about Java, we can say that Java is Pass by Value and not pass by reference.

We will illustrate the up-quoted statement by programming.

Illustration with Program

Let’s say we have a class Car like below.

public class Car {

private String color;

public Car () {}

public Car (String a) {

this.color=a; }

public String getColor() {

return color;

public void setColor (String color) {

this.color = color;

}

Next we have a program which swaps two objects.

public class Disp {

public static void main(String[] args) {

Car red = new Car("Red"); 

Balloon yellow = new Balloon("Yellow"); 

swap(red, yellow);

System.out.println("red color="+red.getColor());

System.out.println("yellow color="+yellow.getColor());

desc(yellow);

System.out.println("yellow color="+yellow.getColor());

}

private static void desc(Car car) { //car=100

balloon.setColor("Red"); //car=100

car= new car("Green"); //car=200

car.setColor("Yellow"); //car = 200

}

// swap method

public static void swap(Object o1, Object o2){

Object temp = o1;

o1=o2;

o2=temp;

}

}

Output

Red color=Red

Yellow color=Yellow

Yellow color=Red

Explanation:

So as I told earlier that JAVA is pass by Value, therefore, we can see that the first two lines in the output the swap () method didn’t work. Let’s do a thorough explanation of the code.

First, we created an instance of a class by using the new operator. It is created and the value is stored at the memory location. Therefore this instance is pointing the memory location of objects that is “red” and “yellow”. Now when we are calling the values with new objects o1 and o2 then it is pointing to the memory location of the two objects that is “red” and “yellow”. So when the swap method gets invoked at first it points to the memory location of “Red”. In the next line, Car reference is changed to the next address and it gets pointed to the memory location of “yellow”. Therefore they get swapped at the second step, not on the first step. This is why JAVA is referred to as Pass by Value and not reference.

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