package java.util;public interface Collection
     
       extends Iterable
      
        {
         //返回该集合中元素的数量     int size();    //判断该集合中元素是否为空 size() == 0    boolean isEmpty();        boolean contains(Object o);        Iterator
       
         iterator();    Object[] toArray();    
        
          T[] toArray(T[] a);     boolean add(E e);    boolean remove(Object o);      boolean containsAll(Collection
          c);    boolean addAll(Collection
          c);    boolean removeAll(Collection
          c);       boolean retainAll(Collection
          c);    void clear();       boolean equals(Object o);    int hashCode();}
        
       
      
     

上面是Collection<T>接口，该接口扩展了Iterator<T>接口

Collection接口是处理对象集合的根接口，接口提供了在集合中添加和删除元素的基本操作。

Collection接口提供的toArray()方法返回一个表示集合的数组。

package java.lang;import java.util.Iterator;/** Implementing this interface allows an object to be the target of *  the "foreach" statement. * @since 1.5 */public interface Iterable
     
       {    /**     * Returns an iterator over a set of elements of type T.     *      * @return an Iterator.     */    Iterator
      
        iterator();}