Java Inheritance: Why calling a method at the parent constructor level, calls the overridden child method?

问题

Calling the fruitName method inside Fruit constructor, is actually delegating the call to the child Apple class's method!

public class CallingParentMethodInInheritanceHierarchy {

abstract class Fruit {
    String fruitName;

    public Fruit(String fruitName) {
        this.fruitName = fruitName;

        /*
         * o/p - Inside constructor - Child: Fruit name is - Apple
         */
        System.out.println("Inside constructor - " + fruitName()); // doubt?
    }

    public String fruitName() {
        return "Parent: Fruit name is - " + fruitName;
    }

    public abstract String type();

}

class Apple extends Fruit {
    public Apple() {
        super("Apple");
    }

    public String fruitName() {
        /*
         * To call the super class method, only way is -
         * 
         * System.out.println(super.fruitName());
         */
        return "Child: Fruit name is - " + fruitName;
    }

    @Override
    public String type() {
        return "AllSeasonsFruit";
    }
}

public static void main(String[] args) {
    Fruit fruit = new CallingParentMethodInInheritanceHierarchy().new Apple();

    /*
     * o/p - Child: Fruit name is - Apple
     */
    System.out.println(fruit.fruitName());
}

}

The main attempt behind this, is that I was trying to call the parent method without using the trivial way super.fruitName() call inside a child method.

Please help me @line #12

回答1:

This is polymorphism 101. The most specific - i.e. lowest on the inheritance tree - version of a method is invoked within a class hierarchy. If you had not overridden the fruitName() method at all then the base class method would be called.

回答2:

Because that's how polymorphism works. Child classes can override any method that is not final, and parent code won't be able to tell the difference. That's why non-abstract non-final public methods are generally discouraged.

来源：https://stackoverflow.com/questions/33845392/java-inheritance-why-calling-a-method-at-the-parent-constructor-level-calls-th

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