What is the usage of super keyword in java

In Java, before executing the constructor of a subclass or the subclass does not explicitly specify a constructor, the parameterless constructor of the parent class will be automatically called.

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Three usage cases of super:

Access the overridden method in the parent class method.

Call the parent class constructor.

Access hidden member variables in the parent class.

Sample code:

class A{ int a; A(){ a = 3; System.out.println(a); } void dosomething(){ System.out.println("A"); } } class B extends A{ int a; B(){ a = 5; System.out.println(a); } void dosomething(){ super.dosomething(); System.out.println("B"); } }

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When executed in the main method

B b = new B(); b.dosomething();

Output result:

3 5 A B

The constructor in the parent class cannot be inherited by the subclass. The subclass can only use its own constructor or the default parameterless constructor.

When the parent class defines a constructor with parameters, and when the subclass defines a constructor without parameters, the compiler automatically adds super() and an error occurs. (The parent class does not have a corresponding no-parameter constructor)

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