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.

(Video tutorial recommendation: java course)

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");
	}
}

(Recommended tutorial: java introductory tutorial)

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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