遍历集合

针对Collection 进行遍历

例

1.使用增强for循环

          for(Object obj:collection){

              System.out.println(obj);

          }

2.使用迭代器

          Iterator it=collection.iterator();

          //hasNext()判断下一个元素是否存在

          while(it.hasNext()){

          //next()将迭代器移动到下一个元素

              Object o=it.next();

              System.out.println(o);

          }

3.对List遍历可以用for循环

          for(int i=0;i<list.size();i++){

              Object obj=list.get(i);

              System.out.println(obj);

          }

4.对Map普通遍历

          Set keySet=map.keySet();

          Iterator  it=keySet.iterator();

          while(it.hasNext()){

              String key=(String) it.next();

              String value=map.get(key);

              System.out.println("key: "+key+" value: "+value);

          }

5.使用泛型后Map遍历

          for(Map.Entry<String, String> entry:map.entrySet()){

              String key=entry.getKey();

              String value=entry.getValue();

              System.out.println("key: "+key+" value: "+value);

          }