this Keyword in Java

this is a keyword in java which can be used inside a method or a constructor to refers to the current object. Except in static methods, this keyword can be used in any method to refer to current object. this keyword can be used to refer to any member variable or member method of current class.

this keyword can be used in multiple ways:

Uses of this Keyword in Java
  • We can declare instance variable and local variables inside a methods having same name. this can be used to differentiate between instance variable and local variable.

  • this can be used to refer to current object.

  • this can be used to invoke methods and constructors of current object.

  • this cab be used to pass current object as parameter to a method call.

  • this can be used to create copy of an object by passing it to the copy constructor.

  • this can be used to return current object from a method.
class Company {
    public void printReference(Company object) {
        System.out.println("Object Reference = " + object);
        System.out.println("this Reference = " + this);
public class ThisObjectReferenceJava {
    public static void main(String[] args) {
        Company myCompany = new Company();
Object Reference = Company@12a3a380
this Reference = Company@12a3a380

In above java program, we created an object named myCompany of the class Company. We then call printReferencemethod to print the reference to myCompany object and this reference of the object.

We can see that the reference of myCompany object and this is exactly same which means this contains reference of current object.

this can be used to refer to current object.

this keyword by default refers to the current object. Inside any member method, you can use this to access any member variable or to invoke any member method. This keyword is mainly used to distinguish between instance variable and local variable of same name.

this.variable will always refer to instance variable.

class MotorBike {
    private boolean isEngineOn = false;

    private void startEngine() {
        this.isEngineOn = true;
        System.out.println("Starting Engine");

    private void startMoving() {
        System.out.println("Bike is Moving");

    public void startBike() {

public class ThisJava {
    public static void main(String[] args) {
        MotorBike myBike = new MotorBike();
Starting Engine
Bike is Moving

In above java program, we are using this to access the member variable and member methods of current object within a method body.

  • Inside method startEngine, we are using this to access member variable isEngineOn of current object.
  • Inside method startBike, we are using this to call two private methods startEngine and startMoving of current onject.

Using this to pass current object as method parameter

We can use this keyword to pass the current object as an argument to a method.

class Book {
    String name;
    int price;

    Book(String name, int price) { = name;
        this.price = price;

    public void incrementPrice(int increaseBy) {
        System.out.println("Before price = " + this.price);
        addToPrice(this, increaseBy);
        System.out.println("After price = " + this.price);

    private void addToPrice(Book book, int amount) {
        book.price += amount;
public class ThisMethodArgumentJava {
    public static void main(String[] args) {
        Book javaBook = new Book("Java Book", 100);
Before price = 100
After price = 120

In above program, we are passing this as argument for addToPrice method of Book. We can pass this as argument to a method which expects an object reference as argument. Since this contains the reference of object javaBook, we can access the member variables of object javaBook inside addToPrice method.

Returning current object from a method

Whenever we want to return current object reference from a member method then we can simply return this.

class Complex {
    int real, imaginary;

    public Complex setReal(int real) {
        this.real = real;
        return this;
    public Complex setImaginary(int imaginary) {
        this.imaginary = imaginary;
        return this;
    public void print() {
        System.out.format("%d + %di\n", 
            this.real, this.imaginary);

public class ThisMethodReturnJava {
    public static void main(String[] args) {
        Complex number = new Complex();
0 + 0i
10 + 5i

In above example, setReal and setImaginary method return reference of current object by returning this. The caller of these two methods can use the return value as the object reference of number.

this is used for constructor overloading

Using this we can call the constructor of a class like this(). this can also be used inside a constructor to invoke another overloaded constructor of same Class, this is called constructor overloading.
For example:
Let's say a class has one constructor without any argument and one constructor with one argument. From no-argument constructor we can call one argument constructor by passing some default value.

class Rectangle {
    int length, width;
    // No-Arg Construtor
    Rectangle() {
        this(0, 0);
    // One Arg Construtor
    Rectangle(int size) {
        this(size, size);
    // All Arg Construtor
    Rectangle(int length, int width) {
        this.length = length;
        this.width = width;

    public void print() {
        System.out.format("Length= %d, Width= %d\n",
                this.length, this.width);
public class ThisConstructorOverloading {
    public static void main(String[] args) {
        Rectangle rect1 = new Rectangle();
        Rectangle rect2 = new Rectangle(5);
        Rectangle rect3 = new Rectangle(10, 20);

Length= 0, Width= 0
Length= 5, Width= 5
Length= 10, Width= 20