java default关键字

在Java中，default是一个关键字，用于在接口中定义默认方法。Java 8引入了默认方法的概念，它允许在接口中提供方法的默认实现，而不需要实现类去实现这些方法。这样可以向现有的接口添加新的方法，而不会破坏实现该接口的现有类。

interface Vehicle {
    // 默认方法
    default void start() {
        System.out.println("Vehicle is starting...");
    }

    // 抽象方法
    void accelerate();
}

class Car implements Vehicle {
    // 实现抽象方法
    @Override
    public void accelerate() {
        System.out.println("Car is accelerating...");
    }
}

class Motorcycle implements Vehicle {
    // 实现抽象方法
    @Override
    public void accelerate() {
        System.out.println("Motorcycle is accelerating...");
    }

    // 重写默认方法
    @Override
    public void start() {
        System.out.println("Motorcycle is starting...");
    }
}

public class Main {
    public static void main(String[] args) {
        Car car = new Car();
        car.start(); // Output: Vehicle is starting...
        car.accelerate(); // Output: Car is accelerating...

        Motorcycle motorcycle = new Motorcycle();
        motorcycle.start(); // Output: Motorcycle is starting...
        motorcycle.accelerate(); // Output: Motorcycle is accelerating...
    }
}