TreeMap 底层是红黑树排序是根据key值进行的添加元素时异常 Comparable异常 Comparator比较自定义对象放在键的位置...-白红宇

TreeMap 底层是红黑树排序是根据key值进行的添加元素时异常 Comparable异常 Comparator比较自定义对象放在键的位置...

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发布时间：2019-06-20

本文共 3917 字，大约阅读时间需要 13 分钟。

package com.swift;import java.util.Comparator;import java.util.HashMap;import java.util.Iterator;import java.util.Map;import java.util.Map.Entry;import java.util.Set;import java.util.TreeMap;public class Map_keySet_entrySet {    public static void main(String[] args) {        /*         * TreeMap 集合存储自定义对象，并使用 2 中方式遍历获取         */                Map
     
       hm = new HashMap
      
       ();        hm.put(new Person("lisi",18), "加拿大");        hm.put(new Person("zhangsa",17), "澳大利亚");        hm.put(new Person("zhangsa",17), "澳大利亚");        hm.put(new Person("wangwu",20), "新加坡");        hm.put(new Person("zhaoliu",19), "新西兰");        hm.put(new Person("zhaoliu",19), "新西兰");        hm.put(new Person("lisa",22), "迪拜");                //使用TreeMap无法排序比较是会出现Comparable错误 这时需要自己弄比较器        Map
       
         tree = new TreeMap
        
         (new Comparator
         
          () {            @Override            public int compare(Person arg0, Person arg1) {                int num=arg0.getAge()-arg1.getAge();                return num==0?arg0.getName().compareTo(arg1.getName()):num;            }                    });        tree.put(new Person("lisisi",18), "china");                //keySet方法一        Set
          
            set=hm.keySet(); for(Person per:set) { System.out.println("人员："+per.toString()+"来自："+hm.get(per)); } Set
           
             set1=tree.keySet(); for(Person per:set1) { System.out.println("人员："+per.toString()+"来自："+tree.get(per)); } //entrySet方法二 for(Map.Entry
            
              en:hm.entrySet()) { System.out.println(); System.out.println("人员："+en.getKey().toString()+"来自："+en.getValue()); } Map
             
               tree1 = new TreeMap
              
               (new Comparator
               
                () { @Override public int compare(Person arg0, Person arg1) { int num=arg0.getAge()-arg1.getAge(); return num==0?arg0.getName().compareTo(arg1.getName()):num; } }); tree1.put(new Person("fengqichanglin",18), "langyabang"); System.out.println(); Iterator
                 it=tree1.entrySet().iterator(); while(it.hasNext()) { Entry
                
                  entry=(Entry
                 
                  ) it.next(); System.out.println(entry.getKey().toString()+entry.getValue()); } }}

package sortmap_demo;import java.util.ArrayList;import java.util.Collections;import java.util.Comparator;import java.util.List;import java.util.Map;import java.util.Map.Entry;import java.util.Set;import java.util.TreeMap;public class CollectionsSort {    public static void main(String[] args) {        Map
     
       map=new TreeMap
      
       ();        map.put(1,new User("张三",28));        map.put(2,new User("李四",29));        map.put(3,new User("王五",30));        map.put(4,new User("赵六",31));        Set
       
        
         > set = map.entrySet();        List
         
          
           > list = new ArrayList
           
            
             >(set); Collections.sort(list,new Comparator
             
              
               >() { @Override public int compare(Entry
               
                 o1, Entry
                
                  o2) { return o2.getValue().getAge()-o1.getValue().getAge(); } }); for (Entry
                 
                   u : list) { System.out.println(u.getKey()+"--"+u.getValue()); }}}

不颠倒key和value的位置，用list集合api排序的方法

TreeMap根据key的Comparator对象排序方法

package sortmap_demo;import java.util.Comparator;import java.util.Map;import java.util.TreeMap;public class HashMapDemo {    public static void main(String[] args) {        Map
     
       map=new TreeMap
      
       (new Comparator
       
        () {            @Override            public int compare(User o1, User o2) {                if(o1.getAge()>o2.getAge()){                    return -1;                }else if(o1.getAge()==o2.getAge()){                     return 0;                }else{                  return 1;                }                      }        });        map.put(new User("张三",28),1);        map.put(new User("李四",29),2);        map.put(new User("王五",30),3);        map.put(new User("赵六",31),4);        for (User u : map.keySet()) {            System.out.println(u+"--"+map.get(u));        }}}