java - 我如何从我的代码中的照片中删除喜欢

Question

我已经为一个照片上传网站编写了一个程序，用户可以在其中为照片点赞，我有一个测试脚本来点赞照片然后显示所有喜欢然后我想删除喜欢并现在显示所有喜欢。我该怎么做？

import java.util.*;

public class Likes {
    private static Hashtable<Photo, TreeSet<User>> likes = new Hashtable<>();

    //like photo
    public static void like(Photo photo, User user) {
        try {
            likes.get(photo).add(user);
        }
        catch (NullPointerException e) {
            likes.put(photo, new TreeSet<>());
            likes.get(photo).add(user);
        }
    }



    //unlike photo
    public static void unlike(Photo photo, User user) {
        try {
            likes.get(photo.remove(user));
        }
        catch (NullPointerException e) {

        }
    }

    //has liked photo
    public boolean hasliked(Photo photo, User user) {
        try {
            return likes.get(photo).contains(user);
        }
        catch (NullPointerException e) {
            return false;
        }
    }

    //get all likes
    public List<Photo> getAllLikes(User user){
        // new empty list
        List<Photo> likedphotos = new ArrayList<Photo>();

        for (Photo photo : likes.keySet()) {
            if(hasliked(photo, user)){
                // add photo to list
                likedphotos.add(photo);
            }
            // return that initial list
        }

        return likedphotos;

    }



    public String toString() {
        return likes.toString();
    }

    public void get(Photo remove) {
    }

    public void remove(Photo photo1, User user1) {
    }
}

测试:

import java.sql.SQLOutput;
import java.util.*;

public class TestDrive {

    public static void main(String[] args) throws InputValidationException {



        //create 2 photo object
        Photo photo1 = new Photo();
        Photo photo2 = new Photo();

        //create 1 user object
        User user1 = new User();

        //create 1 like object
        Likes likes1 = new Likes();


        //set 2 photos
        photo1.setimageURL("photo of user 2");
        photo2.setimageURL("photo of user 1");

        //print the 2 photos
        System.out.println(photo1.getimageURL());
        System.out.println(photo2.getimageURL());


        //set 1 user
        user1.setUserName("oopnoob");

        //print the username
        System.out.println(user1.getUserName());

        //Like the 2 photos


        Likes.like(photo1, user1);
        Likes.like(photo2, user1);

        //Test the hasliked method to see if user1 has liked both photos - both should return true

        System.out.println("Should be true: " + likes1.hasliked(photo1, user1));
        System.out.println("Should be true: " + likes1.hasliked(photo2, user1));


        //Test the getAllLikes for user1. Should print 2 photos.

        System.out.println("user1 liked: " + likes1.getAllLikes(user1));


//i dont know how to remove the like from the photo

        //Test the unlike feature by unliking photo1

        likes1.unlike(photo1, user1);


        //Test the getAllLikes - should only print one photo

        System.out.println("user1 liked: " + likes1.getAllLikes(user1));







    }

}

Answer 1

基于你的这部分代码

   //unlike photo
public static void unlike(Photo photo, User user) {
    try {
        likes.get(photo.remove(user));
    }
    catch (NullPointerException e) {

    }
}

您似乎是在删除照片而不是“赞”

代码应该是

    //unlike photo
public static void unlike(Photo photo, User user) {
    try {
        likes.get(photo).remove(user);
    }
    catch (NullPointerException e) {

    }
}

注意:在类中捕获 NullPointerException 是一个非常糟糕的主意。如果您认为像 photo 或 user 这样的值可以为 null，最好在使用该值之前进行检查。捕获异常然后忽略它也不明智。感谢@Ghostcat 向我指出这一点。