Super This Keyword in Java

Super Keyword

Super in java is a keyword which is a reference variable. It is used to refer to the immediate superclass object or instance variable. The word super came into usage because of the concept of inheritance. The keyword super is placed inside a subclass to call a method from a superclass.

Syntax:

super.a; //for Variable

super.m1(); //for Method

super(); // for Constructor

Remember the points given below:

• We must have super class subclass relationship in our program.

• Super can be applied to variable, constructors, and method.

• Super keyword always represents super class object.

• It's generally used to bypass global variable with the same name.

• Super call to constructor must be at first line of all constructors.

• We strictly cannot call super () in methods in any line; this rule applies only to super() not to super.a or super.m1().

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This Keyword

This keyword in java is used inside a method or constructor of a class. It is used to refer to a member of a current object within the instance of a method or constructor.

• This represents current class object

• Can be applied to variable, constructor and method

Syntax:

this.a; // variable case

this.m1(); // method case

this(10); // To call parameterize constructor of current class object

Remember the points given below:

• In case of variable, same class’s global variable will get called

• Call to constructor by using this ‘this()’ must be a first line of constructor only. This means that we cannot add ‘this()’ anywhere other than the first line of constructor

• inside method ‘this()’ is not allowed, that is call to constructor not allowed by using this.

• JVM never puts automatically this() keyword like super()

• If we wrote call to constructor explicitly by using ‘this()’ the ‘super()’ call to constructor will not be put by JVM

• Recursion will be there as we call the same class constructor using this() in same constructor, which is not allowed in java

Difference between Super and This