急急急!!!! 一个JAVA题 帮我写下程序

这个怎样，因为用了set，所以没用list.。
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

public class UserManager {

Set userSet = new HashSet();

public static void main(String[] args) {
UserManager manager = new UserManager();
User user1 = new User();
User user2 = new User();
user1.setId(1);
user1.setName("jack");
user2.setId(2);
user2.setName("lucy");

manager.addUser(user1);
manager.addUser(user2);
manager.removeUser(user1);
manager.isExist(user1);
manager.show();
}

private void show() {
System.out.println("当前有" + userSet.size() + "个用户:");
for (Iterator iterator = userSet.iterator(); iterator.hasNext();) {
System.out.println(iterator.next());
}

}

private void isExist(User user) {
if(userSet.contains(user)) {
System.out.println("该用户存在");
}
System.out.println("该用户不存在");
}

private void removeUser(User user) {
userSet.remove(user);
System.out.println("删除用户:" + user);
}

private void addUser(User user) {

userSet.add(user);
System.out.println("添加用户:" + user);
}
}

class User {
private int id;
private String name;

public User() {

}

public int getId() {
return id;
}

public String getName() {
return name;
}

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

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

public String toString() {
return id + " " + name;
}
}

你好，按照你的要求，代码如下：

import java.util.HashSet;

public class UserManager {

HashSet set = new HashSet();

public void add(User user) {
set.add(user);
}

public void del(User user) {
set.remove(user);
}

public boolean isExist(User user) {
return set.contains(user);
}

public void print(User user) {
System.out.println(user.toString());
}
}

class User {
String name;

public String toString() {
return "姓名: " + name;
}
}

import java.util.HashSet;

public class UserManager {

HashSet set = new HashSet();

public void add(User user) {
set.add(user);
}

public void del(User user) {
set.remove(user);
}

public boolean isExist(User user) {
return set.contains(user);
}

public void print(User user) {
System.out.println(user.toString());
}
}

class User {
String name;

public String toString() {
return "姓名: " + name;
}
}