Java super keyword
In java, super is a keyword used to refers to the parent class object. The super keyword came into existence to solve the naming conflicts in the inheritance. When both parent class and child class have members with the same name, then the super keyword is used to refer to the parent class version.
In java, the super keyword is used for the following purposes.
- To refer parent class data members
- To refer parent class methods
- To call parent class constructor
🔔 The super keyword is used inside the child class only.
super to refer parent class data members
When both parent class and child class have data members with the same name, then the super keyword is used to refer to the parent class data member from child class.
Let's look at the following example java code.
class ParentClass{
int num = 10;
}
class ChildClass extends ParentClass{
int num = 20;
void showData() {
System.out.println("Inside the ChildClass");
System.out.println("ChildClass num = " + num);
System.out.println("ParentClass num = " + super.num);
}
}
public class SuperKeywordExample {
public static void main(String[] args) {
ChildClass obj = new ChildClass();
obj.showData();
System.out.println("\nInside the non-child class");
System.out.println("ChildClass num = " + obj.num);
//System.out.println("ParentClass num = " + super.num); //super can't be used here
}
}
When we run this code, it produce the following output.
super to refer parent class method
When both parent class and child class have method with the same name, then the super keyword is used to refer to the parent class method from child class.
Let's look at the following example java code.
class ParentClass{
int num1 = 10;
void showData() {
System.out.println("\nInside the ParentClass showData method");
System.out.println("ChildClass num = " + num1);
}
}
class ChildClass extends ParentClass{
int num2 = 20;
void showData() {
System.out.println("\nInside the ChildClass showData method");
System.out.println("ChildClass num = " + num2);
super.showData();
}
}
public class SuperKeywordExample {
public static void main(String[] args) {
ChildClass obj = new ChildClass();
obj.showData();
//super.showData(); // super can't be used here
}
}
When we run this code, it produce the following output.
super to call parent class constructor
When an object of child class is created, it automatically calls the parent class default-constructor before it's own. But, the parameterized constructor of parent class must be called explicitly using the super keyword inside the child class constructor.
Let's look at the following example java code.
class ParentClass{
int num1;
ParentClass(){
System.out.println("\nInside the ParentClass default constructor");
num1 = 10;
}
ParentClass(int value){
System.out.println("\nInside the ParentClass parameterized constructor");
num1 = value;
}
}
class ChildClass extends ParentClass{
int num2;
ChildClass(){
super(100);
System.out.println("\nInside the ChildClass constructor");
num2 = 200;
}
}
public class SuperKeywordExample {
public static void main(String[] args) {
ChildClass obj = new ChildClass();
}
}
When we run this code, it produce the following output.
To call the parameterized constructor of the parent class, the super keyword must be the first statement inside the child class constructor, and we must pass the parameter values.