Java中如何使用TreeMap实现按键排序

TreeMap<String, Integer> map = new TreeMap<>();
map.put("banana", 2);
map.put("apple", 1);
map.put("orange", 3);
<p>// 输出时会按 key 的字典序排列
map.forEach((k, v) -> System.out.println(k + ": " + v));
// 输出：
// apple: 1
// banana: 2
// orange: 3</p>

TreeMap<String, Integer> map = new TreeMap<>(Collections.reverseOrder());
map.put("banana", 2);
map.put("apple", 1);
map.put("orange", 3);
<p>map.forEach((k, v) -> System.out.println(k + ": " + v));
// 输出：
// orange: 3
// banana: 2
// apple: 1</p>

class Person {
    String name;
    int age;
    Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
}
<p>TreeMap<Person, String> map = new TreeMap<>((p1, p2) -> p1.age - p2.age);
map.put(new Person("Alice", 30), "Engineer");
map.put(new Person("Bob", 25), "Designer");
map.put(new Person("Charlie", 35), "Manager");</p><p>// 按年龄升序输出</p>

for (Map.Entry<String, Integer> entry : map.entrySet()) {
    System.out.println(entry.getKey() + " -> " + entry.getValue());
}