THIS KEYWORD : JAVA Programming by "Gopal Krishna"

1) The this keyword can be used to refer current class instance variable.

If there is ambiguity between the instance variable and parameter, this keyword resolves the problem of ambiguity.

Understanding the problem without this keyword

Let's understand the problem if we don't use this keyword by the example given below:

class Student10{  
    int id;  
    String name;  
      
    student(int id,String name){  
    id = id;  
    name = name;  
    }  
    void display(){System.out.println(id+" "+name);}  
  
    public static void main(String args[]){  
    Student10 s1 = new Student10(111,"Karan");  
    Student10 s2 = new Student10(321,"Aryan");  
    s1.display();  
    s2.display();  
    }  
} 

Output:0 null
       0 null

In the above example, parameter (formal arguments) and instance variables are same that is why we are using this keyword to distinguish between local variable and instance variable.

Solution of the above problem by this keyword

//example of this keyword  
class Student11{  
    int id;  
    String name;  
      
    Student11(int id,String name){  
    this.id = id;  
    this.name = name;  
    }  
    void display(){System.out.println(id+" "+name);}  
    public static void main(String args[]){  
    Student11 s1 = new Student11(111,"Karan");  
    Student11 s2 = new Student11(222,"Aryan");  
    s1.display();  
    s2.display();  
}  
}  

Output111 Karan
       222 Aryan

class base
{
base()
{
System.out.println("i am base class");
}
base(int i)
{
System.out.println("i am perametrised");
}
}

class derived extends base
{ 
String s;
int a;
public static void main(String args[])
{

derived x=new derived("hello",4);
}

derived (int i)
{
super(i);
System.out.println("the value of i ->"+i);
}
derived (String s,int a)
{
//this(i);
System.out.println("the value of s="+s);
System.out.println("the value of a="+a);

}
}