java 集合转map实现自定义key

Java集合可以通过使用Map接口来实现自定义Key。以下是一些示例代码：

1. 使用HashMap实现自定义Key

Map<Person, String> map = new HashMap<>();
Person p1 = new Person("Tom", 25);
Person p2 = new Person("Jerry", 30);
map.put(p1, "Tom's value");
map.put(p2, "Jerry's value");

class Person {
    private String name;
    private int age;
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    //重写hashCode和equals方法
    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }
    @Override
    public boolean equals(Object obj) {
        if (this == obj) return true;
        if (obj == null || getClass() != obj.getClass()) return false;
        Person person = (Person) obj;
        return age == person.age && Objects.equals(name, person.name);
    }
}

2. 使用TreeMap实现自定义Key，并按照Key排序

Map<Person, String> map = new TreeMap<>(new Comparator<Person>() {
    @Override
    public int compare(Person o1, Person o2) {
        int result = o1.getName().compareTo(o2.getName());
        if (result == 0) {
            result = o1.getAge() - o2.getAge();
        }
        return result;
    }
});
Person p1 = new Person("Tom", 25);
Person p2 = new Person("Jerry", 30);
map.put(p1, "Tom's value");
map.put(p2, "Jerry's value");

class Person {
    private String name;
    private int age;
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    //getter方法和重写hashCode和equals方法
    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }
    @Override
    public boolean equals(Object obj) {
        if (this == obj) return true;
        if (obj == null || getClass() != obj.getClass()) return false;
        Person person = (Person) obj;
        return age == person.age && Objects.equals(name, person.name);
    }
}

在使用TreeMap实现自定义Key时，需要实现一个Comparator接口，该接口用于比较两个对象的大小。在该例中，按照姓名升序排序，如果姓名相同，则按照年龄升序排序。