如何进入哈希映射中的值数组？

Question

我正在学习 Java，所以这可能是一个简单的问题。

我有一个哈希图：

private final HashMap<String, String[]> hobbies= new HashMap<String, String[]>();

并且其中只有一个键和几个值的条目很少。 在我的任务中，我需要创建一个方法，该方法将使用这些数组中的指向值的每个键带到另一个列表

示例（如果键“Adam”包含值“Yoga”，请将其添加到列表中）

我的问题是我不知道如何进入该值数组进行比较。

下面是我的代码。 我知道这是错误的以及为什么，但我不知道下一步该怎么做。

package com.company;

import java.util.*;

public class Hobbies {
    private final HashMap<String, String[]> hobbies = new HashMap<String, String[]>();

    public void add(String hobbyist, String... hobbies) {
            this.hobbies.put(hobbyist,hobbies);
    }
    //Implement method that returns a list of names of people with the selected hobby in any order
    public List<String> findAllHobbyists(String hobby){


        LinkedList<String> finalMap = new LinkedList<>();

        for(int i=0; i<hobbies.size();i++){
            
          
            if(hobbies.values().toArray()[0].equals(hobby)){

                finalMap.add(hobbies.keySet().toArray()[i].toString());
            }
      
        }

        return finalMap;
    }

    public static void main(String[] args) {
        Hobbies hobbies = new Hobbies();
        hobbies.add("Steve","Fashion","Piano","Reading");
        hobbies.add("Patty","Drama","Magic","Pets");
        hobbies.add("Chad","Puzzles","Pets","Yoga");


        System.out.println(Arrays.toString(hobbies.findAllHobbyists("Yoga").toArray()));
    }
    }

Answer 1

我的问题是我不知道如何进入该值数组进行比较。

假设这是你的问题。 方法values()就是你要找的。 您还可以检查方法keySet()以查看它是否可以帮助您完成手头的任务。

您还应该在您正在编辑代码的 IDE 中查找自动格式化。更小、更简洁的代码可以让您在 Stack Overflow 中更快、更具体地获得答案。

Answer 2

试试下面的代码：

package com.company;
import java.util.*;

public class Hobbies {
    private final HashMap<String, String[]> hobbies = new HashMap<String, String[]>();

    public void add(String hobbyist, String... hobbies) {
        this.hobbies.put(hobbyist, hobbies);
    }

    //Implement method that returns a list of names of people with the selected hobby in any order
    public List<String> findAllHobbyists(String hobby) {
        LinkedList<String> finalList = new LinkedList<>();

        Set<Map.Entry<String, String[]>> entries = hobbies.entrySet();
        for (Map.Entry<String, String[]> entry : entries) {
            if (isPresent(entry.getValue(), hobby))
                finalList.add(entry.getKey());
        }
        return finalList;
    }

    private boolean isPresent(String[] array, String value) {
        for (String s : array) {
            if (s.equals(value))
                return true;
        }
        return false;
    }

    public static void main(String[] args) {
        Hobbies hobbies = new Hobbies();
        hobbies.add("Steve", "Fashion", "Piano", "Reading");
        hobbies.add("Patty", "Drama", "Magic", "Pets");
        hobbies.add("Chad", "Puzzles", "Pets", "Yoga");


        System.out.println(Arrays.toString(hobbies.findAllHobbyists("Yoga").toArray()));
    }
}

要阅读有关 HashMap 的更多信息，请单击此处

Answer 3

请看下面的代码片段。 希望它能让您了解如何访问存储为哈希映射中的值的字符串数组

import java.io.*;
import java.util.*;
public class Main
{
    public static void main(String[] args) {
        System.out.println("Hello World");
        String[] val = {"Yoga", "Eat", "Sleep"};
        HashMap<String, String[]> hobbies= new HashMap<String, String[]>();
        hobbies.put("Adam", val);
        String[] vals = hobbies.get("Adam");
        System.out.println(vals[0]);
    }
}

Answer 4

您可以使用name和hobbies属性定义 Person 对象

public class Person {
    
    String name;
    List<String> hobbies;
// getter and setters
    
}

创建 Person 对象列表

//create Person object and set name and hoobies
        Person p1 = new Person();
        List<String> steveHobbies = new ArrayList<>();
        steveHobbies.add("Fashion"); 
        steveHobbies.add("Piano");
        steveHobbies.add("Reading");
        
        p1.setName("steve");
        p1.setHobbies(steveHobbies);
        
        Person p2 = new Person();
        List<String> pattyHobbies = new ArrayList<>(); 
        pattyHobbies.add("Drama"); 
        pattyHobbies.add("Magic");
        pattyHobbies.add("Pets"); 
        
        p2.setName("patty");
        p2.setHobbies(pattyHobbies);
        
        Person p3 = new Person();
        List<String> chadHobbies = new ArrayList<>();
        chadHobbies.add("Puzzles"); 
        chadHobbies.add("Pets");
        chadHobbies.add("Yoga");
        
        p3.setName("chad");
        p3.setHobbies(chadHobbies);

// Add persons to list
        List<Person> persons = new ArrayList<>();
        persons.add(p1);
        persons.add(p2);
        persons.add(p3);

使用列表上的流，过滤具有所需爱好的人

        persons.stream().filter(p -> p.getHobbies().contains("Yoga")).forEach(p -> System.out.println("Person with matching Hobby:"+p.getName()));

输出：

Person with matching  Hobby:chad

要查找以Pets为爱好的人，您可以将contains("Yoga")更改为contains("Pets")

输出：

Person with matching Hobby:patty
Person with matching Hobby:chad