HashMap遍历方法
java Map遍历速度最优解
第一种（效率高）：
Map map = new HashMap();
Iterator iter = mat.entrySet().iterator();
while(iter.hasNext()){
Map.Entry entry = (Map.Entry)iter.next();
Object key = entry.getKey();
Object val = entry.getValue();
}
第二种（效率低）：
Map map = new HashMap();
Iterator iter = mat.entrySet().iterator();
while(iter.hasNext()){
Object key = iter.next();
Object val = map.get(key);
}
HashMap的遍历有两种常用方法：使用keyset及entryset进行遍历，但两者的便利速度有差别，下面请看实例：
public class HashMapTest{
public static void main(String[] args)...{
HashMap hashmap = new HashMap();
for(int i=0;i<1000;i)...{
hashmap.put("i","thanks");
}
long bs = Calendar.getInstance().getTimeInMillis();
Iterator iterator = hashmap.keySet().iterator();
while(iterator.hasNext())...{
System.out.print(hashmap.get()iterator.next());
}
System.out.println();
System.out.println(Calendar.getInstance().getTimeInMillis() - bs);
listHashMap();
}
public static void listHashMap()...{
java.util.HashMap hashmap = new java.util.HashMap();
for (int i = 0;i<1000;i)...{
hashmap.put("i","thanks");
}
long bs = Calendar.getInstance().getTimeInMillis();
java.util.Iterator it = hashmap.entrySet().iterator();
while(it.hasNext())...{
java.util.Map.Entry entry = (java.util.Map.Entry)it.next();
//entry.getKey()返回与此项对应的键
//entry.getValue(）返回与此项对应的值
System.out.print(entry.getValue());
}
System.out.println();
System.out.println(Calendar.getInstance().getTimeInMillis() - bs);
}
}
对于keySet其实是遍历了2次一次是转为iterator，一次就从hashmap中取出key所对应的value，而entry只遍历了一次，把key和value都放到了entry中，所以就快了
