java - 从 HashSet 中删除连接到键的值？

Question

我想从学校类(class)中撤回一名学生。下面的方法不是去掉值吗？请提出想法:

public static void withdrawStudent(String student) {
    enrollments.values().remove(student);

}

public static void main(String[] args) {
        enroll("101", "Pat");
        withdrawStudent("Pat");
}

//这是类(class)的一部分。

private static HashMap<String, Set<String>> enrollments = new HashMap<String, Set<String>>();

public static void enroll(String unit, String student) { 
    Set<String> studentsSet = enrollments.get(unit); 
    if(studentsSet == null) { 
        studentsSet = new HashSet<>(); 
    } 
    studentsSet.add(student);
    enrollments.put(unit, studentsSet); 
}

Answer 1

您的问题是您试图删除一个字符串，而 enrollments.values() 返回一组字符串。一个可能的解决方法是这样，但请记住，这会将学生从每次注册中删除。

public static void withdrawStudent(String student) {
    for (Set<String> studentSet : enrollments.values()) {
        studentSet.remove(student);

    }
}