map对值排序

/**  *   */ package com.fritt.planmanage.util; import java.util.ArrayList; import java.util.Comparator; import java.util.LinkedHashMap; import java.util.Map; import java.util.Map.Entry; import edu.emory.mathcs.backport.java.util.Collections; /**  * @author lf  *   */ public class SortMap { public  static Map<String, Integer> sortMap(Map<String, Integer> oldMap) { ArrayList<Map.Entry<String, Integer>> list =  new ArrayList<Map.Entry<String, Integer>>(oldMap.entrySet()); Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() { @Override public int compare(Entry<java.lang.String, Integer> arg0, Entry<java.lang.String, Integer> arg1) { return arg1.getValue() - arg0.getValue();           //对map值进行降序排序 } }); Map<String, Integer> newMap = new LinkedHashMap<String, Integer>(); for (int i = 0; i < list.size(); i++) { newMap.put(list.get(i).getKey(), list.get(i).getValue()); } return newMap; } public  static Map<String, Double> sortMap_Double(Map<String, Double> oldMap) { ArrayList<Map.Entry<String, Double>> list =  new ArrayList<Map.Entry<String, Double>>(oldMap.entrySet()); Collections.sort(list, new Comparator<Map.Entry<String, Double>>() { @Override public int compare(Entry<java.lang.String, Double> arg0, Entry<java.lang.String, Double> arg1) { return arg1.getValue().compareTo(arg0.getValue()); } }); Map<String, Double> newMap = new LinkedHashMap<String, Double>(); for (int i = 0; i <list.size(); i++) { newMap.put(list.get(i).getKey(), list.get(i).getValue()); } return newMap; } public  static Map<String, String> sortMap_String(Map<String, String> oldMap) { ArrayList<Map.Entry<String, String>> list =  new ArrayList<Map.Entry<String, String>>(oldMap.entrySet()); Collections.sort(list, new Comparator<Map.Entry<String, String>>() { @Override public int compare(Entry<String, String> arg0,Entry<String,String> arg1) { return arg0.getValue().compareTo(arg1.getValue());      //升序排序 } }); Map<String, String> newMap = new LinkedHashMap<String, String>(); for (int i = list.size()-1; i >=0; i--) {                        //从后向前导入，相当于降序 newMap.put(list.get(i).getKey(), list.get(i).getValue()); } return newMap; }

}

HashMap:输入的<key,value>对是乱序插入，比较快，key不允许重复

TreeMap:有序，对输入的<key,value>进行排序，默认将按照key值进行升序排序，key不允许重复，若重复，后面的覆盖前面的

LinkedHashMap:它保留插入的顺序，如果需要输出的顺序和输入时的相同，那么就选用LinkedHashMap。

IdentityHashMap:key允许重复，只要两个key的地址不相等即可。

public class Test {              public static void main(String[] args) {                      //不指定排序器           TreeMap<String, String> treeMap1 = new TreeMap<String, String>();           treeMap1.put("2", "1");           treeMap1.put("b", "1");           treeMap1.put("1", "1");           treeMap1.put("a", "1");           System.out.println("treeMap1="+treeMap1);              //指定排序器           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("2", "1");           treeMap2.put("b", "1");           treeMap2.put("1", "1");           treeMap2.put("a", "1");           System.out.println("treeMap2="+treeMap2);       }   }  

 

执行输出结果：

Java代码   treeMap1={1=1, 2=1, a=1, b=1}   treeMap2={b=1, a=1, 2=1, 1=1}