java HashMap使用示例，javahashmap示例,package cn.o

java HashMap使用示例，javahashmap示例,package cn.o

package cn.outofmemory.snippets.core;import java.util.HashMap;import java.util.Set;public class KeySetHashMap {  public static void main(String[] args) {    // Create a HashMap and populate it with elements    HashMap hashMap = new HashMap();    hashMap.put("key_1","value_1");    hashMap.put("key_2","value_2");    hashMap.put("key_3","value_3");    /*       Set keySet() operation returns a Set containing all keys in HashMap.       The key set is backed by the HashMap thus elements removed from the       key set will also be removed from the originating HashMap.       Nevertheless it is not permitted to add an element to the resultant key set and       java.lang.UnsupportedOperationException exception will be thrown in case we try to.    */    Set keySet = hashMap.keySet();    System.out.println("keySet contains : " + keySet);    keySet.remove("key_2");    System.out.println("after removing key_2 from keySet, keySet contains : " + keySet + " hashMap contains : " + hashMap);  }}

输出：

keySet contains : [key_3, key_2, key_1]after removing key_2 from keySet, keySet contains : [key_3, key_1] hashMap contains : {key_3=value_3, key_1=value_1}