java中的equals怎么用 equals比较的5个重写规范

public class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public boolean equals(Object obj) {
        // 1. 检查是否是同一个对象
        if (this == obj) {
            return true;
        }

        // 2. 检查是否为 null
        if (obj == null) {
            return false;
        }

        // 3. 检查是否是同一个类
        if (getClass() != obj.getClass()) {
            return false;
        }

        // 4. 类型转换
        Person other = (Person) obj;

        // 5. 比较关键字段
        return this.age == other.age &&
               (this.name == null ? other.name == null : this.name.equals(other.name));
    }

    @Override
    public int hashCode() {
        // 如果重写了 equals 方法，强烈建议重写 hashCode 方法
        // 保证 equals 相等的对象，hashCode 也相等
        int result = 17;
        result = 31 * result + (name == null ? 0 : name.hashCode());
        result = 31 * result + age;
        return result;
    }

    public static void main(String[] args) {
        Person p1 = new Person("Alice", 30);
        Person p2 = new Person("Alice", 30);
        Person p3 = new Person("Bob", 25);

        System.out.println(p1.equals(p2)); // true
        System.out.println(p1.equals(p3)); // false
    }
}

class Point {
    private int x;
    private int y;

    public Point(int x, int y) {
        this.x = x;
        this.y = y;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null || getClass() != obj.getClass()) {
            return false;
        }
        Point other = (Point) obj;
        return x == other.x && y == other.y;
    }

    @Override
    public int hashCode() {
        int result = 17;
        result = 31 * result + x;
        result = 31 * result + y;
        return result;
    }
}

class ColorPoint extends Point {
    private String color;

    public ColorPoint(int x, int y, String color) {
        super(x, y);
        this.color = color;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null || getClass() != obj.getClass()) { // 使用 getClass()
            return false;
        }
        ColorPoint other = (ColorPoint) obj;
        return super.equals(obj) && (color == null ? other.color == null : color.equals(other.color));
    }

    @Override
    public int hashCode() {
        int result = super.hashCode();
        result = 31 * result + (color == null ? 0 : color.hashCode());
        return result;
    }
}