Java-Map的遍历

package collection;
/**
 * 遍历map的4种方法
 */
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

public class ErgodicMap {
	public static void main(String[] args) {
		Map<String, String> map = new HashMap<String, String>();
		  map.put("1", "value1");
		  map.put("2", "value2");
		  map.put("3", "value3");
		  
		  //第一种：广泛使用，二次取值
		  System.out.println("经过Map.keySet遍历key和value：");
		  for (String key : map.keySet()) {
		   System.out.println("key= "+ key + " and value= " + map.get(key));
		  }
		  
		  //第二种
		  System.out.println("经过Map.entrySet使用iterator遍历key和value：");
		  Iterator<Map.Entry<String, String>> iterator = map.entrySet().iterator();
		  while (iterator.hasNext()) {
		   Map.Entry<String, String> entry = iterator.next();
		   System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
		  }
		  
		  //第三种：推荐，尤为是容量大时
		  System.out.println("经过Map.entrySet遍历key和value");
		  for (Map.Entry<String, String> entry : map.entrySet()) {
		   System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
		  }
		 
		  //第四种
		  System.out.println("经过Map.values()遍历全部的value，但不能遍历key");
		  for (String value : map.values()) {
		   System.out.println("value= " + value);
		  }

	}

}