Java基础巩固系列 TreeMap

代码示例:

public class TestMap {

    //定制排序
    @Test
    public void test5(){
        Comparator com = new Comparator() {

            @Override
            public int compare(Object o1, Object o2) {
                if (o1 instanceof Customer && o2 instanceof Customer) {
                    Customer c1 = (Customer) o1;
                    Customer c2 = (Customer) o2;
                    int i = c1.getId().compareTo(c2.getId());
                    if (i == 0){
                        return c1.getName().compareTo(c2.getName());
                    }else {
                        return i;
                    }
                }
                return 0;
            }
        };
        TreeMap map = new TreeMap(com);
        map.put(new Customer("AA",1001),89);
        map.put(new Customer("CC",1001),79);
        map.put(new Customer("MM",1004),99);
        map.put(new Customer("GG",1002),69);

        Set key1 = map.keySet();
        for (Object obj : key1) {
            System.out.println(obj + "--->" + map.get(obj));
        }
    }

    //自然排序
    @Test
    public void test4(){
        Map map = new TreeMap();
        map.put(new Person("AA",23),89);
        map.put(new Person("MM",22),79);
        map.put(new Person("GG",23),99);
        map.put(new Person("JJ",13),69);

        Set key1 = map.keySet();
        for (Object obj : key1) {
            System.out.println(obj + "--->" + map.get(obj));
        }
    }


}

结果1：

Customer{name='AA', id=1001}--->89
Customer{name='CC', id=1001}--->79
Customer{name='GG', id=1002}--->69
Customer{name='MM', id=1004}--->99

结果2：

Person{name='JJ', age=13}--->69
Person{name='MM', age=22}--->79
Person{name='AA', age=23}--->89
Person{name='GG', age=23}--->99

 总结：

TreeMap:按照添加进Map中的元素的key的指定属性进行排序。要求：key必须是同一个类的对象！

                                                     针对key：自然排序 vs 定制排序