学步园

java中没有指针的概念，但是有对象的引用，java中链表的实现就是通过对象的引用实现的。下面是一个链表的简单实现

class Link {
	
	class Element {
		public Object value = null;
		public Element nextNode = null;
	}
	
	private Element header = null;
	
	public void add(Object node) {
		if (header == null) {
			header = new Element();
			header.value = null;
			header.nextNode = null;
		}
		
		Element element = new Element();
		element.value = node;
		element.nextNode = header.nextNode;
		header.nextNode = element;
	}
	
	public boolean remove(Object obj) {
		if (header == null) {
			return false;
		}
		
		Element pre = header;
		Element ele = header.nextNode;
		while(ele != null) {
			if (ele.value == obj) {
				pre.nextNode = ele.nextNode;
				return true;
			}
			pre = ele;
			ele = ele.nextNode;
		}
		return false;
	}
	
	public void clear() {
		header = null;
	}
	
	public boolean contains(Object obj) {
		if (header == null) {
			return false;
		}
		
		Element elm = header.nextNode;
		while(elm != null) {
			if (elm.value == obj) {
				return true;
			}
			elm = elm.nextNode;
		}
		
		return false;
	}
	
	public Element getElement(int index) {
		if (header == null) {
			return null;
		}
		
		if (index > (this.Size()-1) || index < 0) {
			return null;
		}
		
		int i = 0;
		Element ele = header.nextNode;
		while(ele != null) {
			if (i == index) {
				return ele;
			}
			i++;
			ele = ele.nextNode;
		}
		return null;
	}
	
	
	public int Size() {
		if (header == null) {
			return 0;
		}
		int size = 0;
		Element ele = header.nextNode;
		while(ele != null) {
			size++;
			ele = ele.nextNode;
		}
		return size;
	}
	
	public boolean checkLoop()
	{
		if (header==null) {
			return false;
		}
		int size = this.Size();
		if (size == 0) {
			return false; 
		}
		Set<Element> set = new HashSet<Element>();
		for (int i = 0; i < size ;i ++) {
			Element el = getElement(i);
			if(!set.contains(el)) {
				set.add(el);
			}
			if(set.contains(el.nextNode)) {
				return true;
			}
		}
		return false;
	 }
}