Java HashMap 集合操作示例：存储老师和课程信息

import java.util.HashMap; import java.util.Map; import java.util.Set;

public class HashMapTest { public static void main(String[] args) { // 创建 HashMap 集合 Map<String, String> teacherMap = new HashMap<>(); // 向集合中存储老师和所教课程信息 teacherMap.put('Tom', 'CoreJava'); teacherMap.put('John', 'Oracle'); teacherMap.put('Susan', 'Oracle'); teacherMap.put('Jerry', 'JDBC'); teacherMap.put('Jim', 'Unix'); teacherMap.put('Kevin', 'JSP'); teacherMap.put('Lucy', 'JSP');

    // 将 Jim 老师的课程修改为 Linux
    teacherMap.put('Jim', 'Linux');

    // 判断有没有 Jack 老师
    if (teacherMap.containsKey('Jack')) {
        System.out.println('有 Jack 老师');
    } else {
        System.out.println('无 Jack 老师');
    }

    // 判断有没有 HTML 课程
    if (teacherMap.containsValue('HTML')) {
        System.out.println('有 HTML 课程');
    } else {
        System.out.println('无 HTML 课程');
    }

    // 求 Susan 老师教哪门课程
    String course = teacherMap.get('Susan');
    System.out.println('Susan 老师教' + course + '课程');

    // 求一共有几门不同的课程，一共有几位老师
    Set<String> courseSet = new HashSet<>();
    Set<String> teacherSet = new HashSet<>();
    for (String value : teacherMap.values()) {
        courseSet.add(value);
    }
    for (String key : teacherMap.keySet()) {
        teacherSet.add(key);
    }
    System.out.println('一共有' + courseSet.size() + '门不同的课程');
    System.out.println('一共有' + teacherSet.size() + '位老师');

    // 有没有一个老师教多个课程
    Map<String, Integer> courseCount = new HashMap<>();
    for (String value : teacherMap.values()) {
        if (!courseCount.containsKey(value)) {
            courseCount.put(value, 1);
        } else {
            int count = courseCount.get(value);
            courseCount.put(value, count + 1);
        }
    }
    boolean flag = false;
    for (int count : courseCount.values()) {
        if (count > 1) {
            flag = true;
            break;
        }
    }
    if (flag) {
        System.out.println('有老师教多门课程');
    } else {
        System.out.println('没有老师教多门课程');
    }

    // 教 JSP 课程的老师的名字，打印出来
    for (Map.Entry<String, String> entry : teacherMap.entrySet()) {
        if ('JSP'.equals(entry.getValue())) {
            System.out.println(entry.getKey() + '教 JSP 课程');
        }
    }

    // 将每门课程的授课老师人数，求出来，存到一个新的 Map 中
    Map<String, Integer> teacherCount = new HashMap<>();
    for (String value : teacherMap.values()) {
        if (!teacherCount.containsKey(value)) {
            teacherCount.put(value, 1);
        } else {
            int count = teacherCount.get(value);
            teacherCount.put(value, count + 1);
        }
    }
    for (Map.Entry<String, Integer> entry : teacherCount.entrySet()) {
        System.out.println(entry.getKey() + '课程有' + entry.getValue() + '位老师授课');
    }
}

}