去除一个list中包含的另一个list的数据

 话不多说，先上代码

public static void main(String[] args) {
		//List<long>类型
		List<Long> list=new ArrayList<>();
		List<Long> list1=Arrays.asList(1L,2L,3L,4L,5L,6L);
		List<Long> list2=Arrays.asList(4L,5L,6L);
		HashSet h1 = new HashSet(list1);
		HashSet h2 = new HashSet(list2);
		h1.removeAll(h2);
		list.addAll(h1);
		System.out.println(list);//打印结果为：[1, 2, 3]
		//List<String>类型 同上
		List<String> s=new ArrayList<>();
		List<String> st=Arrays.asList("a","b","c","d");
		List<String> str=Arrays.asList("a","b","c");
		HashSet hs1 = new HashSet(st);
		HashSet hs2 = new HashSet(str);
		hs1.removeAll(hs2);
		s.addAll(hs1);
		System.out.println(s);//打印结果为：[d]

	}

 延伸：如果要去除List<Object>呢？是否还可以?

1、创建一个User对象

public class User {

	private Integer userId;
	private String username;
	private int sex;
	private Integer age;
	
	public Integer getUserId() {
		return userId;
	}
	public void setUserId(Integer userId) {
		this.userId = userId;
	}
	public String getUsername() {
		return username;
	}
	public void setUsername(String username) {
		this.username = username;
	}
	public int getSex() {
		return sex;
	}
	public void setSex(int sex) {
		this.sex = sex;
	}
	public Integer getAge() {
		return age;
	}
	public void setAge(Integer age) {
		this.age = age;
	}
	public User() {
		super();
	}
	public User(Integer userId, String username, int sex, Integer age) {
		super();
		this.userId = userId;
		this.username = username;
		this.sex = sex;
		this.age = age;
	}
	@Override
	public String toString() {
		return "User [userId=" + userId + ", username=" + username + ", sex=" + sex + ", age=" + age + "]";
	}
	
	
}

2、同样的方法

public static void main(String[] args) {
        List<User> uList=new ArrayList<User>();
		uList.add(new User(1, "xxx", 1, 11));
		uList.add(new User(2, "zzz", 1, 11));
		uList.add(new User(3, "aaa", 1, 11));
		uList.add(new User(4, "bbb", 1, 11));
		
		List<User> uList1=new ArrayList<User>();
		uList1.add(new User(1, "xxx", 1, 11));
		HashSet h3 = new HashSet(uList);
		HashSet h4 = new HashSet(uList1);
		h3.removeAll(h4);
		uList.removeAll(uList1);
		uList.clear();
		uList.addAll(h3);
		//[User [userId=3, username=aaa, sex=1, age=11], User [userId=1, username=xxx, sex=1, age=11], User [userId=2, username=zzz, sex=1, age=11], User [userId=4, username=bbb, sex=1, age=11]]
		System.out.println(uList);//结果并不是想要的
}

3、怎样才能做到去除list里的对象呢？

• 重写hashCode和equals方法

//重写hashCode和equals
	@Override
	public int hashCode() {
		String result = username+userId;
		return result.hashCode();
	}
	@Override
	public boolean equals(Object obj) {
		User u = (User)obj;
		return this.getUsername().equals(u.getUsername()) && (this.getUserId().equals(u.getUserId()));
	}

同上代码 重新运行  结果如下图所示：