浅谈list.removeAll()删除失败的原因及解决

public class User {
 private String name;
 private int age;
 private String sex;
  //private Company company; // Company 类也要重写 hashCode() 和 equals() 方法
 
  //省略getter setter方法
 
 public User(String name, int age, String sex) {
 super();
 this.name = name;
 this.age = age;
 this.sex = sex;
 }
 
 public User() {
 super();
 } 
 
 @Override
 public String toString() {
 return "User [name=" + name + ", age=" + age + ", sex=" + sex + "]";
 }
}

import java.util.ArrayList;
import java.util.List;
 
public class TestRemoveAll { 
 public static void main(String[] args) {
 //
 List allList = new ArrayList();
 allList.add(new User("张三",18,"男"));
 allList.add(new User("李四",20,"女"));
 //
 List list = new ArrayList();
 list.add(new User("张三",18,"男"));
 // 测试 
 if(allList.removeAll(list)){
 System.out.println("删除成功！");
 System.out.println(allList);
 }else{
 System.out.println("删除失败！");
 System.out.println(allList);
 }
 }
}

import java.util.ArrayList;
import java.util.List;
 
public class TestRemoveAll {
 
 public static void main(String[] args) {
 //
 List allList = new ArrayList();
 allList.add(new User("张三",18,"男"));
 allList.add(new User("李四",20,"女"));
 //
 User user = new User("张三",18,"男");
 // 测试 
 if(allList.contains(user)){
 System.out.println("我重写了hashCode() equals() 方法 ,所以打印此条！");
 }else{
 System.out.println("若未重写hashCode() equals() 方法 ,则打印此条！");
 }
 } 
}