Java集合之Map详解-优快云博客

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package com.guogf.tigger.Map;

import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.TreeMap;

public class TestMapSort {

   public static void main(String[] args) {
       testHashMap();
       testTreeMap1();
       testTreeMap2();
       testLinkHashMap();
   }
   public static void testHashMap(){
       Map<String, String> map = new HashMap<String, String>();
map.put("1", "Level 1");
map.put("2", "Level 2");
map.put("3", "Level 3");
map.put("a", "Level a");
map.put("b", "Level b");
map.put("c", "Level c");
Iterator<Entry<String, String>> it = map.entrySet().iterator();
while (it.hasNext()) {
Entry<String, String> e = it.next();
System.out.println("testHashMap===>Key: " + e.getKey() + "; Value: " + e.getValue());
}
   }
   //TreeMap如不指定排序器，默认将按照key值进行升序排序，如果指定了排序器，则按照指定的排序器进行排序。
   public static void testTreeMap1(){

Map<String, String> map = new TreeMap<String, String>();
map.put("1", "Level 1");
map.put("3", "Level 3");
map.put("2", "Level 2");
map.put("a", "Level a");
map.put("b", "Level b");
map.put("c", "Level c");
Iterator<Entry<String, String>> it = map.entrySet().iterator();
while (it.hasNext()) {
Entry<String, String> e = it.next();
System.out.println("testTreeMap1===>Key: " + e.getKey() + "; Value: " + e.getValue());
}
   }

   //TreeMap指定排序器，
   public static void testTreeMap2(){
       TreeMap<String, String> treeMap2 = new TreeMap<String, String>(new Comparator<String>(){
/*
* int compare(Object o1, Object o2) 返回一个基本类型的整型，
* 返回负数表示：o1 小于o2，
* 返回0 表示：o1和o2相等，
* 返回正数表示：o1大于o2。
*/
public int compare(String o1, String o2) {
//指定排序器按照降序排列
return o2.compareTo(o1);
}
});
treeMap2.put("1", "Level 1");
treeMap2.put("3", "Level 3");
treeMap2.put("2", "Level 2");
treeMap2.put("a", "Level a");
treeMap2.put("b", "Level b");
treeMap2.put("c", "Level c");
Iterator<Entry<String, String>> it =treeMap2.entrySet().iterator();
while (it.hasNext()) {
   Entry<String, String> e = it.next();
   System.out.println("testTreeMap2===>Key: " + e.getKey() + "; Value: " + e.getValue());
}
   }
   //LinkedHashMap 根据输入顺序输出
   public static void testLinkHashMap(){
       Map<String, String> map = new LinkedHashMap<String, String>();
       map.put("1", "Level 1");
       map.put("5", "Level 3");
       map.put("4", "Level 2");
       map.put("6", "Level a");
       map.put("2", "Level b");
       map.put("c", "Level c");
       Iterator<Entry<String, String>> it = map.entrySet().iterator();
       while (it.hasNext()) {
           Entry<String, String> e = it.next();
           System.out.println("LinkedHashMap===>Key: " + e.getKey() + "; Value: " + e.getValue());
       }
   }
}