泛型

import java.util.ArrayList;import java.util.HashMap;import java.util.Iterator;import java.util.List;import java.util.Map;import java.util.Set;import java.util.Map.Entry;public class GenericTest {public static void main(String[] args) {/* * 格式：类型<类型[,类型...]> * * 泛型使用必须前后相同 * * 泛型是在编译前进行类型约束，在字节码文件中不存在泛型信息 */List<String> list = new ArrayList<String>();list.add("abc");//list.add(123);Map map = new HashMap();map.put(123, 123);//没有泛型的map 的遍历Set s = map.entrySet();Iterator ite = s.iterator();while(ite.hasNext()){Map.Entry entry = (Entry) ite.next();Integer key = (Integer) entry.getKey();Integer value = (Integer) entry.getValue();System.out.println("*** " + key + ":" + value);}Map<String,Integer> map2 = new HashMap<String, Integer>();map2.put("123", 456);map2.put("abc", 789);//遍历map  [key,value][key,value]//map2.keySet()  获得所有的键值 keySet<Map.Entry<String,Integer>> set = map2.entrySet();  //获得每一组 Entry(key,value)//迭代器Iterator<Entry<String,Integer>> it = set.iterator();while(it.hasNext()){Map.Entry<String, Integer> entry = it.next();String key = entry.getKey();Integer value = entry.getValue();System.out.println(key + ":" + value);}}}