Introduction to Super Keyword in Java
Super is a keyword that is used to call a function or method in the superclass. This will be defined inside the sub-class. Methods that are only public and protected can be called by using this keyword. In other words, Private methods and static methods cannot be called using this. The super keyword in java can also be used in order to call the constructors of the parent class. Syntax, examples and further details of super keyword will be discussed in the following sections.
Syntax
super.<<method-name>> or super([0 or more arguments]);
How does Super Keyword work in Java?
As already mentioned, super can be used in several occasions. They are used:
- To refer instance variable of an immediate parent class.
- To refer to the method of an immediate parent class.
- To refer the constructor of an immediate parent class.
Now, let us see each of them in detail.
1. To Refer Instance Variable of an Immediate Parent Class
If the parent and child class have the same data members, Super keyword can be used to access the field or data member of the parent class. Ambiguity for Java Virtual Machine can occur in this case.
Example:
class A {
protected String name="ann";
}
class B extends A {
public String name="Anna";
public void hello() {
System.out.println("I am " + name);
System.out.println("I am " + super.name);
}
}
Here, two classes A and B have a common field name. A function printType() inside child class uses the super keyword to refer the field in a parent class.
2. To Refer Method of An Immediate Parent Class
Method overriding is a process by which a child class declares the same function or method that is already available in the parent class. Suppose, if a call to the method happens from the object of the child class, then the method in the child class only will be called. In order to access the parent method, a super keyword can be used.
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Example:
class A {
protected String name="ann";
public void hello() {
System.out.println("I am " + name);
}
}
class B extends A {
public String name="Anna”;
public void hello() {
System.out.println("I am " + name);
}
public void test()
{
hello();
super.hello();
}
}
Here, two classes A and B have same method hello(). With the help of a super keyword in test() function, it is possible to access the hello() method of a parent class.
3. To Refer Constructor of Immediate Parent Class
It is already known that a constructor (default) gets automatically called when the object of a class is created. The super keyword can be used to explicitly call the constructor of the superclass from the constructor of the subclass. Make sure that super is used only inside the constructor of the subclass and it is the first statement inside that.
Example:
class A {
//constructor of parent class
A() { System.out.println("I am Kavya Madhavan");
}
}
//child class
class B extends A {
//constructor of child class
B() {
super();
System.out.println("I am Dileep Menon"); } }
Examples of Super Keyword in Java
Below are the different examples mentioned:
Example #1
In the following program, a common variable name is present and super is used to call the variable in a parent class.
//Java program to illustrate Super keyword to refer instance variable
//parent class
class A {
protected String name="ann";
}
//child classs
class B extends A {
public String name="Anna";//variable which is same in parent class
//sample method
public void hello() {
System.out.println("I am " + name);
System.out.println("I am " + super.name);
}
}
//main class
public class SuperExample {
public static void main(String[] args) {
B objb=new B();//object of child class
objb.hello();//call the method in child class
}
}
Output:
Example #2
This program helps in demonstrating the super keyword while referring to the same method in a parent class. Here, hello() is a method that is available in both classes.
//Java program to illustrate Super keyword to refer same method in parent class
//parent class
class A {
protected String name="ann";
public void hello() {
System.out.println("I am " + name);
}
}
//child classs
class B extends A {
public String name="Anna";//variable which is same in parent class
//sample method which is same in parent class
public void hello() {
System.out.println("I am " + name);
}
//method to call the hello() method in parent and child class
public void test()
{
hello();
super.hello();
}
}
//main class
public class SuperExample {
public static void main(String[] args) {
B objb=new B();//object of child class
objb.test();//call the method in child class
} }
Output:
Example #3
This program calls the constructor of the parent class using the super keyword.
//Java program to illustrate Super keyword to refer constructor in parent class
//parent class
class A {
//constructor of parent class
A() {
System.out.println("I am Kavya Madhavan");
}
}
//child class
class B extends A {
//constructor of child class
B() {
super();
System.out.println("I am Dileep Menon");
}
}
//main class
public class SuperExample {
public static void main(String[] args) {
B objb=new B();//object of child class
}
}
Output:
Example #4
This program demonstrates the usage of a super keyword to refer to the parameterized constructor of a parent class.
//Java program to illustrate Super keyword to refer parameterised constructor in parent class
//parent class
class A {
//constructor of parent class
A() {
System.out.println("I am Kavya Madhavan");
}
//parameterised constructor
A(String name) {
System.out.println("I am " + name);
}
}
//child class
class B extends A {
//constructor of child class
B() {
super("Renuka");
System.out.println("I am Dileep Menon");
}
}
//main class
public class SuperExample {
public static void main(String[] args) {
B objb=new B();//object of child class
}
}
Output:
Conclusion
Super is a keyword in Java which is used to refer to the methods or functions, instance variables or attributes and constructors in the parent class. If a constructor is not declared, the compiler automatically creates a default constructor. Similarly, Compiler calls super() automatically if it is not declared. In this document, several aspects of the super keyword are explained in detail.
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