javaHashMap遍历的三种方式以及效率对比

/* HashMap */
public static void hashMap(){
Map hashMap = new HashMap();

for(int i=0;i<100000;i++)
hashMap.put(i+"", i+"v");

long time = System.currentTimeMillis();
System.out.println("==============方式1：通过遍历keySet()遍历HashMap的value");
Iterator it = hashMap.keySet().iterator();
while(it.hasNext()){
hashMap.get(it.next());
//System.out.println(hashMap.get(it.next()));
}
System.out.println("用时:"+(System.currentTimeMillis() - time));


time = System.currentTimeMillis();
System.out.println("==============方式2：通过遍历values()遍历HashMap的value");
Collection values = hashMap.values();
for(Iterator valIt = values.iterator();valIt.hasNext();){
valIt.next();
}
System.out.println("用时:"+(System.currentTimeMillis() - time));


time = System.currentTimeMillis();
System.out.println("==============方式3：通过entrySet().iterator()遍历HashMap的key和映射的value");
Iterator> entryIt = hashMap.entrySet().iterator();
while(entryIt.hasNext()){
Entry entry = entryIt.next();
entry.getKey();
entry.getValue();
//System.out.println("key:"+entry.getKey()+" value:"+entry.getValue());
}
System.out.println("用时:"+(System.currentTimeMillis() - time));

}