HashMap的遍历和排序

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1.HashMap的遍历

package com.sheepmu;import java.util.HashMap;import java.util.Iterator;import java.util.Map;import java.util.Map.Entry;public class KMPText {public static void main(String[] args){ Map<String,String> map=new HashMap<String,String>(); map.put("key1", "bb"); map.put("key0", "aaa"); map.put("key3", "dddd");  map.put("key2", "cccccccc");  //遍历方法0                  我个人最喜欢的遍历。集合的遍历还是用for-each的遍历是最爽滴~ for(Map.Entry<String, String> entry:map.entrySet())//值和value都需要遍历时 { String key= entry.getKey().toString(); String value=entry.getValue().toString();      System.out.println("entry--->"+entry);//  System.out.println("key---->"+key+"    value---->"+value+"   "); }    //遍历方法1                       此方法效率也很高 Iterator it=map.entrySet().iterator(); while(it.hasNext()) { Map.Entry entry=(Map.Entry) it.next(); String key= entry.getKey().toString(); String value=entry.getValue().toString();  System.out.println("key---->"+key+"    value---->"+value+"   "); } }}

2.HashMap的排序

（1）.方法：把map的entry取出来放到list里面，这样就相当于排list

eg:对上面例子的HashMap按key从小到大排orvalue从长到短排

package com.sheepmu;import java.util.ArrayList;import java.util.Collections;import java.util.Comparator;import java.util.HashMap;import java.util.Iterator;import java.util.List;import java.util.Map;import java.util.Map.Entry;public class KMPText {public static void main(String[] args){ Map<String,String> map=new HashMap<String,String>(); map.put("key1", "bb"); map.put("key0", "aaa"); map.put("key3", "dddd");  map.put("key2", "cccccccc");  //遍历 hashmap for(Map.Entry<String, String> entry:map.entrySet())  { String key= entry.getKey().toString(); String value=entry.getValue().toString();   System.out.println("key---->"+key+"    value---->"+value+"   "); } //按要求排序hashmap List<Map.Entry<String, String>> list=new ArrayList<Map.Entry<String, String>>(map.entrySet());//!!!  Collections.sort(list, new Comparator<Map.Entry<String, String>>(){//按key值字符串比较从小到大@Overridepublic int compare(Entry<String, String> o1,Entry<String, String> o2) { return o1.getKey().compareTo(o2.getKey());}});    System.out.println("list---->"+list);    Collections.sort(list, new Comparator<Map.Entry<String, String>>(){//按value值字符串长度比较从大到小@Overridepublic int compare(Entry<String, String> o1,Entry<String, String> o2) { return o2.getValue().length()-o1.getValue().length();}});    System.out.println("list---->"+list);}}

注：如果希望遍历后的顺序与put进去的顺序一致，则采用LinkendHashMap

package com.sheepmu; import java.util.HashMap;import java.util.LinkedHashMap;import java.util.Map;public class KMPText {public static void main(String[] args){ Map<String,String> map=new HashMap<String,String>(); map.put("key1", "bb"); map.put("key0", "aaa"); map.put("key3", "dddd");  map.put("key2", "cccccccc"); System.out.println("hashmap--->"+map);   Map<String,String> lmap=new LinkedHashMap<String,String>(); lmap.put("key1", "bb"); lmap.put("key0", "aaa"); lmap.put("key3", "dddd");  lmap.put("key2", "cccccccc"); System.out.println("linkedhashmap--->"+lmap);   }}

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