集合框架里Iterator迭代器内部实现原理：使用内部类

	/*												
	 * 集合框架里Iterator内部实现原理：使用内部类												
		interface Collection											
		{											
		}											
		interface Iterator											
		{											
			public boolean hasNext();										
			public Object next();										
		}											
													
		class ArrayList											
		{											
			public Iterator iterator()										
			{										
				return new Itr();									
			}										
													
													
			private class Itr implements Iterator										
			{										
				public boolean hasNext()									
				{									
					code...;								
				}									
				public Object next()									
				{									
					code...;								
				}									
			}										
		}											
													
		class ArrayList1											
		{											
			public Iterator iterator()										
			{										
				return new Itr();									
			}										
													
													
			private class Itr implements Iterator										
			{										
				public boolean hasNext()									
				{									
					code...;								
				}									
				public Object next()									
				{									
					code...;								
				}									
			}										
		}											
		*/