Practice›Java Fundamentals›Module 7. Inheritance & Polymorphism›7.2 Overriding

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7.2 Overriding — replacing an inherited method

Lesson

Giving a subclass its own version

A subclass can override an inherited method: define a method with the same signature (same name and parameters). Then, when that method is called on a subclass object, the subclass's version runs instead of the superclass's. Mark it with @Override — the compiler checks that you really are overriding an inherited method.

Worked example

class Dog extends Animal {
    @Override
    public String describe() {   // same signature as Animal's describe()
        return getName() + " is a dog";
    }
}

Animal a = new Animal("Generic");
Dog d = new Dog("Rex");
System.out.println(a.describe());   // "Generic is an animal"
System.out.println(d.describe());   // "Rex is a dog" — Dog's version

Same method name, different result: the object's actual class decides which version runs.

▶ Try it: run this — describe() gives one answer for an Animal and another for a Dog.

class Animal {
    private String name;
    public Animal(String name) { this.name = name; }
    public String getName() { return name; }
    public String describe() { return name + " is an animal"; }
}
class Dog extends Animal {
    public Dog(String name) { super(name); }
    @Override
    public String describe() { return getName() + " is a dog"; }
}
public class Main {
    public static void main(String[] args) {
        Animal an = new Animal("Generic");
        Dog d = new Dog("Rex");
        System.out.println(an.describe());
        System.out.println(d.describe());
    }
}

To override a method, the subclass defines a method with...

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When describe() is called on a Dog object, Java runs...

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Type exactly what this program prints.

class Animal { String n; Animal(String x){n=x;} String describe(){return n+" is an animal";} }
class Dog extends Animal { Dog(String x){super(x);} String describe(){return n+" is a dog";} }
public class Main { public static void main(String[] a){
    System.out.println(new Animal("Gen").describe());
    System.out.println(new Dog("Rex").describe());
}}

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@Override tells the compiler that...

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True or false?

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