问题描述

(c.remove(new Name("f1","l1")));为什么没被移除

import java.util.*;

public class BasicContainer {
public static void main(String[] args) {
Collection c = new HashSet();
c.add("hello");
c.add(new Name("f1","l1"));
c.add(new Integer(100));
c.remove("hello");
c.remove(new Integer(100));
System.out.println
(c.remove(new Name("f1","l1")));
System.out.println(c);
}

}

class Name implements Comparable {
private String firstName,lastName;
public Name(String firstName, String lastName) {
this.firstName = firstName; this.lastName = lastName;
}
public String getFirstName() { return firstName; }
public String getLastName() { return lastName; }
public String toString() { return firstName + " " + lastName; }

public boolean equals(Object obj) {
    if (obj instanceof Name) {
        Name name = (Name) obj;
        return (firstName.equals(name.firstName))
            && (lastName.equals(name.lastName));
    }
    return super.equals(obj);
    }
    public int hashCode() {
        return firstName.hashCode();
    }

    public int compareTo(Object o) {
    Name n = (Name)o;
    int lastCmp =
        lastName.compareTo(n.lastName);
    return
         (lastCmp!=0 ? lastCmp :
          firstName.compareTo(n.firstName));
}

}

解决方案

remove是new出来的对象，hashmap是通过hashcode区分是不是同一个对象的。
两个对象的hashcode不一样，除非你重写一下name类的hashcode获取方式。

解决方案二：

你这样操作会不会报要删除的元素不存在？

解决方案三：

1. 重写hashCode， equal方法
2. 不能直接删除，采用iterator迭代删除