TreeMap按照key排序

package test.tool.gui.common;  
  
import java.util.Comparator;  
import java.util.TreeMap;  
  
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);  
    }  
}  

实际应用中有:

 

 

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Map<String,String> map = new HashMap<>();                   //排序         Map<String, String> map = new TreeMap<String, String>(                 new Comparator<String>() {                     public int compare(String obj1, String obj2) {                         // 升序排序                         return obj1.compareTo(obj2);                     }                 });