Question

有人可以告诉我我的代码有什么问题。即使遵循链接Why do I need to override the equals and hashCode methods in Java?

，我也无法弄明白

import com.sun.org.apache.xpath.internal.operations.Equals;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Scanner;

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

public class Test {

    public static void main(String[] args) {

        Employee a = new Employee(1, "Ram");
        Employee b = new Employee(1, "Ram");
        Employee c = a;
        System.out.println(b.equals(a));
        System.out.println(a.hashCode());
        System.out.println(b.hashCode());

        HashMap<Employee, String> hm = new HashMap<Employee,String>();
        hm.put(a, "one");
        System.out.println(hm.containsKey(b));

        Iterator<Map.Entry<Employee, String>> itr = hm.entrySet().iterator();
        while (itr.hasNext()) {
            Map.Entry<Employee,String> ent = itr.next();
            System.out.println("key "+ent.getKey() +" value " +ent.getValue());
      }


    }

}

class Employee {

    private int id;
    private String name;

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

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

    public boolean equals(Employee obj)
    {
           if(this.id==obj.id)
               return true;
           else
               return false;
    }
    public int hashCode()
    {
        int result =1;
        return (result*37+(name!=null? name.hashCode():0));
    }



}

我重写了equals和hashcode方法，这样我的两个员工对象是相同的。当我在地图中搜索b对象时，由于b的hashCode与a的相同，接下来它在a和b上搜索相等，这是真的。为什么hm.contains（b）在我的代码中返回false，这应该是真的

Answer 1

你的equals方法必须覆盖Object.equals（Object obj）：

public boolean equals(Employee obj)

应该是

public boolean equals(Object obj)

HashMap重写equals和hashcode

1 个答案: