HashMap的遍历和排序
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 @Override public 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 @Override public 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); } }