如何從列表創建ConcurrentHashMap <Student> [等候接聽]

Question

我有一個Student對象List ，需要使用Java 8創建ConcurrentHashMap<String, List>

輸入-> List<Student>輸出-> ConcurrentHashMap<String,List<Student>>

Answer 1

從您的問題尚不清楚，地圖值List將包含哪些內容，但假設它類似於學生姓名列表。

您可以使用Collectors.toConcurrentMap() ：

import java.util.stream.Collectors;

然后是這樣的：

studentList.stream().collect(
    Collectors.toConcurrentMap(Student::getId, Student::getNames));

這是完整的代碼示例：

public static class Student {
    private final String id;
    private final List<String> names;

    public Student(String id, String...names) {
        this.id = id;
        this.names = Arrays.asList(names);
    }

    public String getId() {
        return id;
    }

    public List<String> getNames() {
        return names;
    }
}

public static void main(String[] args) throws Exception {
    List<Student> studentList = new ArrayList<>();
    studentList.add(new Student("fred", "Fred", "Bloggs"));
    studentList.add(new Student("bob", "Bob", "Bobbins"));

    ConcurrentMap<String, List<String>> map = studentList.stream().collect(
            Collectors.toConcurrentMap(Student::getId, Student::getNames));

    System.out.println(map.get("bob").get(1));
}

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