Why Should an Interface Extend Another Interface in Java?

Under what circumstances do we extend one interface from another in Java?

interface A {
    public void method1();
}

interface B extends A {
    public void method2();
}

class C implements B {
    @Override public void method1() {}
    @Override public void method2() {}
}

In Java, an interface can extend another interface to enhance its capabilities by inheriting the method signatures of the parent interface. This allows for a more structured hierarchy and promotes code reusability and polymorphism.

interface A {
    public void method1();
}

interface B extends A {
    public void method2();
}

class C implements B {
    @Override public void method1() { /* Implementation */ }
    @Override public void method2() { /* Implementation */ }
}

Causes

• To create a common contract between interfaces that share common methods.
• To improve code organization by grouping related functionalities into a single interface.
• To facilitate polymorphic behavior in classes that implement multiple interfaces.

Solutions

• Use inheritance for adding common methods to various interfaces, thus allowing the child interface to integrate both parent and its own methods.
• Utilize interface inheritance to enforce a contract across different classes that implement the interface.

Mistake: Assuming that interface inheritance is unnecessary if methods can be defined independently.

Solution: Understand that extending interfaces allows for a more structured design and reduces redundancy.

Mistake: Neglecting to override inherited methods in the implementing class.

Solution: Always ensure that all abstract methods from the parent interfaces are properly implemented in the subclass.