TreeMap

TreeMap

TreeMap实现了Map接口，基于红黑树（Red-Black tree）实现，是一个有序的key-value集合。该映射根据其键的自然顺序进行排序，或者根据创建映射时提供的 Comparator 进行排序，具体取决于使用的构造方法。

构造方法

1.TreeMap()
创建一个空的tree map，按照keys的自然顺序

2. TreeMap(Comparator<? super K> comparator)
   创建一个空的tree map，按照给定comparator的顺序
3. TreeMap(Map<? extends K, ? extends V> m)
   创建包含给定map的新tree map，按照keys的自然顺序
4. TreeMap(SortMap<K, ? extends V> m)
   创建包含给定map的新tree map，按照给定map的顺序排序

常用方法

void	clear()Removes all of the mappings from this map.
Object	clone()Returns a shallow copy of this TreeMap instance.
V	put(K key, V value)Associates the specified value with the specified key in this map.
boolean	containsKey(Object key)Returns true if this map contains a mapping for the specified key.
boolean	containsValue(Object value)Returns true if this map maps one or more keys to the specified value.
Set<Map.Entry<K,V>>	entrySet()Returns a Set view of the mappings contained in this map.
V	get(Object key)Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
Set<K>	keySet()Returns a Set view of the keys contained in this map.
Map.Entry<K,V>	lastEntry()Returns a key-value mapping associated with the greatest key in this map, or null if the map is empty.
V	remove(Object key)Removes the mapping for this key from this TreeMap if present.
int	size()Returns the number of key-value mappings in this map.
Collection<V>	values()Returns a Collection view of the values contained in this map.

遍历

1. for循环遍历

for (Map.Entry entry : mapCollection.entrySet()) {
    // other code
}

2. Iterator遍历

 Set set = mapCollection.entrySet();
Iterator iterator = mapCollection.entrySet().iterator();
while (iterator.hasNext()) {
     Map.Entry entry = (Map.Entry) iterator.next();
     // other code
}

举个栗子

import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

public class TreeMapDemo {
    public static void main(String[] args) {
        TreeMap<Integer, String> tmap = new TreeMap<Integer, String>();
        tmap.put(1, "apple");
        tmap.put(3, "banana");
        tmap.put(24, "cat");
        tmap.put(12, "dog");
        tmap.put(10, "egg");
        tmap.put(15, "fish");

        for (Map.Entry entry : tmap.entrySet()) {
            System.out.printf("key is " + entry.getKey()+" ");
            System.out.println("value is " + entry.getValue());
        }

        Set set = tmap.entrySet();
        Iterator iterator = set.iterator();
        while (iterator.hasNext()) {
            Map.Entry entry = (Map.Entry) iterator.next();
            System.out.printf("key is " + entry.getKey()+" ");
            System.out.println("value is " + entry.getValue());
        }


    }
}

运行结果：

key is 1 value is apple
key is 3 value is banana
key is 10 value is egg
key is 12 value is dog
key is 15 value is fish
key is 24 value is cat