What is this
this is a keyword in Java. It can be used inside the method or constructor of a class. It(this) works as a reference to the current object, whose method or constructor is being invoked. This keyword can refer to any member of the current object from within an instance method or a constructor.
this keyword with a field(Instance Variable)
this keyword in java can be handy in the handling of Variable Hiding. We can not create two instances/local variables with the same name. However, it is legal to create one instance variable & one local variable or Method parameter with the same name. In this scenario, the local variable will hide the instance variable; this is called Variable Hiding.
Example of Variable Hiding
class JBT {
int variable = 5;
public static void main(String args[]) {
JBT obj = new JBT();
obj.method(20);
obj.method();
}
void method(int variable) {
variable = 10;
System.out.println("Value of variable :" + variable);
}
void method() {
int variable = 40;
System.out.println("Value of variable :" + variable);
}
}The output of the above program
Value of variable :10
Value of variable :40As you can see in the example above, the instance variable is hiding, and the value of the local variable (or Method Parameter) is displayed, not the instance variable. To solve this problem, use this keyword to point to the instance variable instead of the local variable.
Example of this keyword in Java for Variable Hiding
class JBT {
int variable = 5;
public static void main(String args[]) {
JBT obj = new JBT();
obj.method(20);
obj.method();
}
void method(int variable) {
variable = 10;
System.out.println("Value of Instance variable :" + this.variable);
System.out.println("Value of Local variable :" + variable);
}
void method() {
int variable = 40;
System.out.println("Value of Instance variable :" + this.variable);
System.out.println("Value of Local variable :" + variable);
}
}The output of the above program
Value of Instance variable :5
Value of Local variable :10
Value of Instance variable :5
Value of Local variable :40this Keyword with Constructor
“this” keyword can be used inside the constructor to call another overloaded constructor in the same class. It is called the Explicit Constructor Invocation. This occurs if a Class has two overloaded constructors, one without argument and another with the argument. Then “this” keyword can call the constructor with an argument from the constructor without argument. This is required as the constructor cannot be called explicitly.
Example of this with Constructor
class JBT {
JBT() {
this("JBT");
System.out.println("Inside Constructor without parameter");
}
JBT(String str) {
System.out
.println("Inside Constructor with String parameter as " + str);
}
public static void main(String[] args) {
JBT obj = new JBT();
}
}The output of the above program
Inside Constructor with String parameter as JBT
Inside Constructor without parameter
As you can see, “this” can invoke an overloaded constructor in the same class.
Note*:
- this keyword can only be the first statement in Constructor.
- A constructor can have either this or super keyword but not both.
this Keyword with Method
this keyword can also be used inside Methods to call another Method from the same Class.
Example of this keyword with Method
class JBT {
public static void main(String[] args) {
JBT obj = new JBT();
obj.methodTwo();
}
void methodOne(){
System.out.println("Inside Method ONE");
}
void methodTwo(){
System.out.println("Inside Method TWO");
this.methodOne();// same as calling methodOne()
}
}The output of the above program
Inside Method TWO
Inside Method ONEExample of this keyword as a Method parameter
public class JBTThisAsParameter {
public static void main(String[] args) {
JBT1 obj = new JBT1();
obj.i = 10;
obj.method();
}
}
class JBT1 extends JBTThisAsParameter {
int i;
void method() {
method1(this);
}
void method1(JBT1 t) {
System.out.println(t.i);
}
}
If you understood this keyword correctly, the next step should be to understand the Static Keyword in Java from Java Tutorial.
class car
{
int speed;
car()
{
speed=70;
}
protected void finalize()
{
System .out.println(“destroy object of car”);
}
}
class bike
{
int speed;
bike()
{
speed=70;
}
protected void finalize()
{
System.out.println(“destroy object of bike”)
}
}
class Garbage_Collection
{
public static void main(String []args)
{
car c=new car();
bike b=new bike();
b=null;
System.gc();
System.out.println(“speed of car: “+c.speed);
}
}
what to do with this code??
class JBT {
public static void main(String[] args) {
JBT obj = new JBT();
obj.methodTwo();
}
void methodOne(){
System.out.println(“Inside Method ONE”);
}
void methodTwo(){
System.out.println(“Inside Method TWO”);
this.methodOne();// same as calling methodOne()
}
}
when I removed ‘this’ from the line this.methodOne();// same as calling methodOne() I get the same output. Is this the standard behaviour ?
Yes, that is standard behavior. this is just used to point to the current object and in this case, it is the current object’s method. So it will get called.
This one is very helpful to understand “this “
cool
Interesting. This is very helpful. Thank you !
thank you …
Elegant content helps me a lot. Thanks
nice
easy to understand
Thank you Akbar
I want to know following statement explanation
int method()
{
return this.variable;
}
here return statement done what task.
Why this place we use.
I simply didn’t get the question. But return is used to return the value of the variable.
Thnx a lot sir….
It is very important concept in java .This keyword is a reference variable that refer the current object in java. This keyword can be used for call current class constructor.
hii
Great and complete explanation of the word “this”. Something basic that many faculty professors wont tell their students…
in which class this() method has been defined
Write a program in Java to implement Method Overloading in java by using “this” keyword ?
wow
nice sharing sir love this site……..
Good examples.
very nice explanation,thnks alot——
“This” helped a lot
Nice…very helpful
got a clean idea.. Thanks.
where is the output of the last program?
very nice
If some one needs to be updated with most recent technologies afterward he must be visit this website and be up to date daily.
this one easy understanding program thanks…
Can you please give the output for the last Example of this keyword as Method parameter. I need only this output for understanding
IT PRINTS THE VALUE OF i ( possibly zero)
Thank you so much
Thank u soo much for helped me.. a good example
it helped me a lot
good
thanks
Very Nice
Nice one!!
very nice explanation,thanx!
I mean method parameter.. Isn’t generate any error??
I is not declared in the example of method to parameter, not necessary??
Nice explanation. Thank you so much.
Very nice.am easily understand
i need a answer for following program
write a java program to implement the usage of “this” keyword for the following cases
1. to refer the current class instance variable.
2. to invoke the current class constructor
3. to invoke the current class method
4. to return current class instance
i need all in one programs with simple codeing…….
i am waiting …!
import java.util.Scanner;
class Bank
{
int accno;
String name;
int bal;
Bank(int accno,String name)
{
this.accno=accno;
this.name=name;
}
Bank(int accno,String name,int bal)
{
this(accno,name);
this.bal=bal;
}
public void show_details()
{
System.out.println(“Accno=”+accno);
System.out.println(“Name=”+name);
System.out.println(“Balance=”+bal);
}
public void deposit()
{
System.out.println(“Enter Amount to be deposit”);
Scanner sc=new Scanner(System.in);
int amount=sc.nextInt();
bal=bal+amount;
show_details();
}
}
public class Ex_this
{
public static void main(String[] args) {
Bank b1=new Bank(1001,”Hari”,1000);
b1.show_details();
b1.deposit();
}
}
show the output
really a very cool website.liked your tutorials,very simple and easy
First of all i thank you
this tutorial was very useful for me.
Very helpful tutorial
the given example this keyword is not best use in method level because without this you can call method…………………………………………………. so please give me best example of this keyword in method level………
Hi Abhishek,
I am agree with you given example is not best example for this @Method level. But i couldn’t think of any other example for the same. Meanwhile i have added an example for Method parameter. WHich might be helpful to you. Would update the article in future in case i get any example.
Thanks
Yes
Scoured the internet to get clarification on this (pun intended). The light bulb finally went on. Thanks.
good help dear
Thank you… it helped a lot ..!
nice
Very nice explanations…
Thanks alot …
very nice tutorial .
okk
this was very helpful..thanks
I Know that no need to tell
Example of this with Constructor has mistake.Can you please make it correct.
Hi Jenith,
I have corrected the output of given program(this keyword for constructor).
Thanks for pointing out this problem. If you find more problems do let me know.
Thanks
i dont know
class A{
A()
{
System.out.println(“hello a”);
}
A(int x){
this();
System.out.println(x);
}
}
class Simple{
public static void main(String args[]){
A a=new A(10);
}
}
i need output sir
output is hello a
10
iam getting error for the constructor example..please let me know the mistake
Could you please let us know the problem you are facing.
You have to create a separate statement for calling the un parameterized constructor…Like this…
A a = new A();