Java this Keyword | this keyword in Java

 

this keyword in Java. If you want to get knowledge and clear understanding about Java this keyword. Then its a best place for you, here i will teach you in detail about Java this keyword with very easy to understand examples.

What is this keyword in Java?

In Java, this keyword can be used in different manners. It can be used to mention class instance variables. To explain it in detail, lets take an example.

Suppose we have a class having one instance variable x and inside this class, we have a constructor that accept one parameter and if variable name for the parameter of constructor is exactly same as class variable, than this will create issue for Java because of ambiguity

Example Program

class ThisExp

{

        int x;

        ThisExp (int x)

        {

                x = x;

        }

        public void show ()

        {

        System.out.println (x); //here we have problem because Class variable name and constructor parameter variable name is same

        }

}

 

public class B

{

        Public static void main (String ar[ ])

        {

                ThisExp obj = new ThisExp(100);

                Obj.show();       

 

        }

}

We will get error in the result because class variable x is assigned to constructor parameter which has exactly same name.

Now to solve this problem, we can use “this” keyword in Java

 

Example Program

class ThisExp

{

        int x;

        ThisExp (int x)

        {

                this.x = x;

        }

        Public void show ()

        {

        System.out.println (x); }

}

 

Public class B

{

        Public static void main (String ar[ ])

        {

                ThisExp obj = new ThisExp(100);

                Obj.show();       

 

        }

}

Now we will get result without any error because local variable and instance variables are distinguished using this keyword which will help us to identify the class instance variable and local variable.

 

When class instance variable and local variable names are different, than there is no need to use this keyword

Example Program without this keyword

class ThisExp

{

        int x;

        ThisExp (int y)

        {

                x = y;

        }

        public void show ()

        {

        System.out.println (x);

}

}

 

public class B

{

        public static void main (String ar[ ])

        {

                ThisExp obj = new ThisExp(100);

                obj.show();       

 

        }

}

 

In the above example, we have no need to use Java this keyword because in this example, class instance variable and local variable are both different.

 

Java this keyword can also be used to call class method, but its optional because if we don’t write this keyword to call the current class method, compiler will put it by itself.

class First

{

        public void a()

        {

        System.out.println(“method a”);

        }

        public void b()

        {

        System.out.println(“method b”);

        this.a();

        }

}

 

We can also call current class constructor using this()

For Example

class Test

{

        Test() //constructor

        {

        System.out.println(“I am constructor”);

        }

        Test(int x) //constructor with one argument

        {

 

        this(); //calling constructor

        System.out.println(x);

        }

}

class Test2

{

        public static void main (String a[])

        {

        Test obj = new Test (3);

        }

}

Output will be

I am constructor

3