instanceof 操作符

概述

instanceof 用于检查对象是否是某个类的实例。

基本概念

用法

if (obj instanceof Type) {
    // obj 是 Type 类型
}

代码示例

基本使用

public class InstanceofBasicDemo {

    static class Animal {}
    static class Dog extends Animal {}
    static class Cat extends Animal {}

    public static void main(String[] args) {
        Animal animal = new Dog();

        // instanceof 检查
        System.out.println(animal instanceof Animal); // true
        System.out.println(animal instanceof Dog);   // true
        System.out.println(animal instanceof Cat);    // false
    }
}

Pattern Matching (JDK 16+)

public class InstanceofPatternDemo {

    static class Animal {}
    static class Dog extends Animal {
        void bark() {
            System.out.println("Woof!");
        }
    }

    public static void main(String[] args) {
        Object obj = new Dog();

        // 传统方式
        if (obj instanceof Dog) {
            Dog dog = (Dog) obj;
            dog.bark();
        }

        // Pattern Matching (JDK 16+)
        if (obj instanceof Dog dog) {
            dog.bark();
        }
    }
}

继承检查

public class InstanceofInheritDemo {

    static class Fruit {}
    static class Apple extends Fruit {}
    static class RedApple extends Apple {}

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

        // 继承链检查
        System.out.println(fruit instanceof Fruit);      // true
        System.out.println(fruit instanceof Apple);       // true
        System.out.println(fruit instanceof RedApple);     // true
    }
}

注意事项

1. 检查继承：子类对象也是父类实例
2. Pattern Matching：JDK 16+ 简化语法
3. 避免 ClassCastException：先检查再转换