Java中equals比较方法使用详解

public class EqualsDemo {
    private String name;
    private int age;
    private double salary;

    //构造函数和getter/setter方法

    // 重写equals方法
    public boolean equals(Object obj) {
        if (obj == this) {  // 如果是同一对象，返回true
            return true;
        }
        if (!(obj instanceof EqualsDemo)) {  // 如果obj不是Employee类对象，返回false
            return false;
        }
        EqualsDemo equalsDemo = (EqualsDemo)obj;  // 强制转换为Employee类对象
        return equalsDemo.name.equals(this.name) && equalsDemo.age == this.age && equalsDemo.salary == this.salary;
    }

    // 重写hashCode方法
    public int hashCode() {
        int result = 17;
        result = 31 * result + name.hashCode();
        result = 31 * result + age;
        long temp = Double.doubleToLongBits(salary);
        result = 31 * result + (int)(temp ^ (temp >>> 32));
        return result;
    }
}

Integer a = new Integer(10);
Integer b = new Integer(10);
System.out.println(a == b); //false
System.out.println(a.equals(b)); //true

package object;
/*
判断两个person对象的内容是否相等
如果两个person对象的各个属性值都一样，则返回true，反之返回false
 */
public class EqualsExercise {
    public static void main(String[] args) {
        Person person1 = new Person("jack", 10, '男');
        Person person2 = new Person("jack", 10, '男');
        System.out.println(person1.equals(person2));   //输出结果是true
    }
}
 
class Person {
    private String name;
    private int age;
    private char gender;
 
    //重写Object的equals方法
    public boolean equals(Object obj) {
        //如果比较的两个对象是同一个对象，则直接返回true
        if (this == obj){   //this就代表调用equals方法的那个对象，obj就是方法里面的实参
            return true;
        }
        //类型判断
        if (obj instanceof Person){  //obj是Person，我们才比较
            //进行 向下转型(即obj转成Person); 因为我需要得到obj的各个属性，如果不转型，拿不到
            Person p = (Person) obj;
            return this.name.equals(p.name) && this.age == p.age && this.gender == p.gender;
        }
        //如果不是person，则直接返回false；总不能拿一个人跟一个狗比
        return false;
    }
 
 
    public Person(String name, int age, char gender) {
        this.name = name;
        this.age = age;
        this.gender = gender;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public int getAge() {
        return age;
    }
 
    public void setAge(int age) {
        this.age = age;
    }
 
    public char getGender() {
        return gender;
    }
 
    public void setGender(char gender) {
        this.gender = gender;
    }
}