Java this Keyword

this keyword

this keyword is used to refer current object of a class.The members of the current object like instance method or field can be referred by using this pointer.

The current execution of object is always pointed by this pointer called as 'object under execution'.

Example - without using this keyword

class WithoutThis
{
    int value;
    String msg;
    WithoutThis(String msg,int value)
    {
	msg = msg;
	value = value;
    }
    void display()
    {
	System.out.println("Without This\n");
	System.out.println("Message : "+msg);
	System.out.println("Value : "+value);
    }
    public static void main(String args[])
    {
	WithoutThis wt = new WithoutThis();
    }
}

Output

Without This

Message : null
Value : 0

In above example we have initialized two variables using Parameterized Constructor. When we run the program we get output as shown above because, in constructor current class fields are not referred that's why values are assigned to same variable only.

Example - Using this keyword

class WithThis
{
    int value;
    String msg;
    WithoutThis(String msg,int value)
    {
	this.msg = msg;
	this.value = value;
    }
    void display()
    {
	System.out.println("With This\n");
	System.out.println("Message : "+msg);
	System.out.println("Value : "+value);
    }
    public static void main(String args[])
    {
	WithThis wt = new WithThis();
    }
}

Output

With This

Message : AndroidBerry
Value : 500

In above example we have used this keyword to refer current class values. that's why have get proper result.

this keyword for calling Constructors

this keyword is also used for calling the constructor functions. It is written inside the constructor to call another constructor

Note : this must be the first statement in the constructor call

Syntax

className()
{
	this(parameter1,parameter2...parameterN);
	...
	...
}

Example

class ThisWithCon
{
    ThisWithCon()
    {
	this(1);
	System.out.println("Im Default ");
    } 
    ThisWithCon(int a)
    {
	this("AndroidBerry",2);
	System.out.println("P1");
    }
    ThisWithCon(String a, int b)
    {
	System.out.println("P2 ");
    }
    public static void main(String args[])
    {
	ThisWithCon twc = new ThisWithCon();
    }
}

Output

P2
P1
Im Default

In above example we have created an object of class called twc. this object called to the default constructor function but, in default constructor we have used this() keyword to call constructor with 1 argument to call Parameterized constructor P1 but P1 again calls for the P2.

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