Java8 -Need for default methods

Category : Java | Sub Category : Java8 Features | By Prasad Bonam Last updated: 2023-11-13 04:51:25 Viewed : 401

Default methods in Java were introduced as part of Java 8 to provide a way to add new methods to interfaces without breaking existing implementations. Before Java 8, interfaces could only declare abstract methods, and any change to an interface would require modifying all classes that implemented that interface. Default methods address this issue and offer several benefits:

  1. Backward Compatibility:

    • Default methods allow interfaces to evolve over time without breaking existing code. Existing implementations of an interface remain compatible with new versions of the interface, even if new methods are added.
  2. API Evolution:

    • Interfaces can now be extended with new methods to accommodate evolving requirements. This is particularly useful in situations where a new method is introduced to an existing interface, and all implementing classes do not need to provide an implementation.
  3. Library Enhancements:

    • Default methods enable library designers to enhance existing interfaces in a backward-compatible way. This is crucial for Java libraries and APIs that want to evolve without forcing users to update their implementations.
  4. Reduced Boilerplate Code:

    • Default methods allow interfaces to provide default implementations for methods. This reduces the amount of boilerplate code that implementing classes need to provide, making it easier to work with and extend existing interfaces.
  5. Interface Extension:

    • Multiple interfaces can provide default implementations for the same method. If a class implements two interfaces that both have default methods with the same signature, the implementing class can choose which default implementation to use or provide its own.
  6. Enhanced Collections API:

    • The introduction of default methods in the Collection interface and its subinterfaces in the Java Collections Framework (e.g., List, Set, Map) allows for more expressive and concise code when working with collections.


public interface Shape { double area(); // Default method providing a default implementation default void printArea() { System.out.println("Area: " + area()); } } public class Circle implements Shape { private double radius; public Circle(double radius) { this.radius = radius; } @Override public double area() { return Math.PI * radius * radius; } } public class Rectangle implements Shape { private double width; private double height; public Rectangle(double width, double height) { this.width = width; this.height = height; } @Override public double area() { return width * height; } }

In this example, the Shape interface has a default method printArea(). Implementing classes such as Circle and Rectangle can choose to use this default method or provide their own implementation. This allows for a common method to be introduced to an existing interface without breaking the implementations.

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