Java HashMap返回值未根据我对equals和hashcode的理解进行确认

Question

以下代码示例的输出是：

{1–e = e2，2–e1 = e1}

package com.sid.practice;

import java.util.HashMap;
import java.util.Map;

public class InputOutputPractice 
{

    public InputOutputPractice() 
    {

    }

    public static void main(String[] args) 
    {
        Employee e = new InputOutputPractice().new Employee(1, "e");
        Employee e1 = new InputOutputPractice().new Employee(2, "e1");
        Employee e2 = new InputOutputPractice().new Employee(1, "e2");

        Map m = new HashMap();
        m.put(e, "e");
        m.put(e1, "e1");
        m.put(e2, "e2");
        System.out.println(m);

    }

    class Employee
    {
        public Employee(int id, String name)
        {
            this.id=id;
            this.name = name;
        }

        private int id;
        private String name;

        public String getName() 
        {
            return name;
        }

        public void setName(String name) 
        {
            this.name = name;
        }

        public int getId() 
        {
            return id;
        }

        public void setId(int id) 
        {
            this.id = id;
        }

        @Override
        public boolean equals(Object obj) 
        {
            return ((Employee)obj).getId()==(this.getId());
        }

        @Override
        public int hashCode() 
        {
            return Integer.valueOf(getId()).hashCode();
        }

        @Override
        public String toString() 
        {
            return this.id + "--" + this.name;
        }
    }
}

我不明白对象如何e2能够覆盖对象中的键e，但不能覆盖值。以我的理解，输出应该是：

{1–e2 = e2，2–e1 = e1}

Answer 1

实际上，您将其倒退了。该值被覆盖。密钥没有被替换，因为就HashMape和e2而言，它们是相同的。

您的输出是{1--e=e2, 2--e1=e1}：

key = e, value = "e2" (which overrode the old value "e")
key = e1, value = "e1"