练习使用HashMap

    技术2022-05-11  10

    import java.util.*; public class TestHashmap{ public static void main(String[] args) {     MapTest map=new MapTest();     map.printMap();     } } class MapTest{     HashMap hash=new HashMap();     public void printMap()     {         hash.put("1","value2");         hash.put("2",null);         hash.put("3","value3");         hash.put("4","value4");         String value=(String)hash.get("3");         System.out.println("key 3<===>"+value);         Set set=hash.keySet();         System.out.println("set size="+set.size());         Iterator it=set.iterator();         while(it.hasNext())         {             String temp2=(String)it.next();             System.out.println("keys contained:"+temp2);             }        Collection valuesList=hash.values();//no exception will be reported if collection        //has null values;  instead, the null value will be printed as "null" if iterated.         System.out.println("valuesList size="+valuesList.size());         Iterator it2=valuesList.iterator();         while(it2.hasNext())         {             String temp2=(String)it2.next();             System.out.println("values contained:"+temp2);             }         List valueList=new ArrayList(hash.values());         for(int i=0;i<valueList.size();i++)         {             String temp=(String)valueList.get(i);             System.out.println("value"+i+"="+temp);  //the sequence is not sure             //can not make sure that the values are displayed according to the input order             }         }     }

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