2022-11-02

一、TreeSet

有排序效果
平衡二叉树、红黑树

TreeSet set = new TreeSet();    
set.add(5);
set.add(3);
set.add(1);
set.add(2);
set.add(4);

image.png

image.png

遍历的顺序 1 2 3 4 5

TreeSet中只能放同一种元素，否则报类型转换异常

二、自定义排序规则

1、

class MyComparator implements Comparator{

    @Override
    public int compare(Villager o1, Villager o2) {
        // TODO Auto-generated method stub
        return o1.getAge() - o2.getAge();
    }   
}

TreeSet set = new TreeSet(new MyComparator());

2、

TreeSet set = new TreeSet(new Comparator() {

            @Override
            public int compare(Villager o1, Villager o2) {
                // TODO Auto-generated method stub
                return o1.getAge() - o2.getAge();
            }
            
        });

3、

public class Villager implements Comparable {}

@Override
    public int compareTo(Villager o) {
        // TODO Auto-generated method stub
        return this.getAge() - o.getAge();
    }

三、Map

image.png

四、HashMap常用方法

1、put
2、get
3、isEmpty
4、containsKey
5、containsValue
6、size
7、clear
8、putAll
9、remove
10、values

五、HashMap存放重复值

HashMap map = new HashMap();
        map.put("a", 1);
        map.put("a", 2);
        System.out.println(map.get("a"));

六、遍历map

Set keySet = map.keySet();
        for(Object obj:keySet) {
            Object value = map.get(obj);
            System.out.println(value);
        }

Set keySet = map.keySet();
        Iterator it = keySet.iterator();
        while(it.hasNext()) {
            Object key = it.next();
            Object value = map.get(key);
            System.out.println(value);
        }

Set entrySet = map.entrySet();
        for(Entry entry : entrySet) {
            System.out.println(entry.getKey());
            System.out.println(entry.getValue());
            System.out.println("~~~~~~~~~~~~~~~~~~~~~");
        }