理解java容器底层原理--手动实现LinkedList

Node

java 中的 LIinkedList 的数据结构是链表，而链表中每一个元素是节点。
我们先定义一下节点：

package com.xzlf.collection;

public class Node {
	Node previous; // 上一个节点
	Node next; // 下一个节点
	Object element; // 元素数据
	
	public Node(Object element) {
		super();
		this.element = element;
	}

	public Node(Node previous, Node next, Object element) {
		super();
		this.previous = previous;
		this.next = next;
		this.element = element;
	}
	
	
}

版本一：基础版本

先创建一个类，完成链表的创建、添加元素、然后重写toString() 方法：

package com.xzlf.collection;

/**
 * 自定义一个链表
 * @author xzlf
 *
 */
public class MyLinkedList {
	private Node first;
	private Node last;
	private int size;
	
	public void add(Object obj) {
		Node node = new Node(obj);
		
		if(first == null) {
			first = node;
			last = node;
		}else {
			node.previous = last;
			node.next = null;
			
			last.next = node;
			last = node;
		}
		size++;
	}
	
	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder("[");
		Node tmp = first;
		while(tmp != null) {
			sb.append(tmp.element + ",");
			tmp = tmp.next;
		}
		sb.setCharAt(sb.length() - 1, ']');
		return sb.toString();
	}
	
	public static void main(String[] args) {
		MyLinkedList list = new MyLinkedList();
		list.add("a");
		list.add("b");
		list.add("c");
		list.add("a");
		list.add("b");
		list.add("c");
		list.add("a");
		list.add("b");
		list.add("c");
		System.out.println(list);
	}
}

测试：

版本二：增加get（） 方法

package com.xzlf.collection;

/**
 * 自定义一个链表
 * 增加get方法
 * @author xzlf
 *
 */
public class MyLinkedList2 {
	private Node first;
	private Node last;
	private int size;
	
	public void add(Object obj) {
		Node node = new Node(obj);
		
		if(first == null) {
			first = node;
			last = node;
		}else {
			node.previous = last;
			node.next = null;
			
			last.next = node;
			last = node;
		}
		size++;
	}
	
	public Object get(int index) {
		Node tmp = null;
		// 判断索引是否合法
		if(index < 0 || index > size - 1) {
			throw new RuntimeException("索引不合法：" + index);
		}
		
		/*索引位置为前半部分，从头部开始找*/
		if (index <= size >> 1) {
			tmp = first;
			for (int i = 0; i < index; i++) {
				tmp = tmp.next;
			} 
		}else {
			/*索引位置为或半部分，从未部开始找*/
			tmp = last;
			for (int i = size -1; i > index; i--) {
				tmp = tmp.previous;
			}
		}
		return tmp.element;
	}
	
	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder("[");
		Node tmp = first;
		while(tmp != null) {
			sb.append(tmp.element + ",");
			tmp = tmp.next;
		}
		sb.setCharAt(sb.length() - 1, ']');
		return sb.toString();
	}
	
	public static void main(String[] args) {
		MyLinkedList2 list = new MyLinkedList2();
		list.add("a");
		list.add("b");
		list.add("c");
		list.add("d");
		list.add("e");
		list.add("f");
		
		System.out.println(list);
		System.out.println(list.get(1));
		System.out.println(list.get(4));
	}
}

测试：

版本三：增加remove() 方法

package com.xzlf.collection;

/**
 * 自定义一个链表
 * 增加remove
 * @author xzlf
 *
 */
public class MyLinkedList3 {
	private Node first;
	private Node last;
	private int size;
	
	public void add(Object obj) {
		Node node = new Node(obj);
		
		if(first == null) {
			first = node;
			last = node;
		}else {
			node.previous = last;
			node.next = null;
			
			last.next = node;
			last = node;
		}
		size++;
	}
	
	public Object get(int index) {
		Node tmp = null;
		// 判断索引是否合法
		if(index < 0 || index > size - 1) {
			throw new RuntimeException("索引不合法：" + index);
		}
		tmp = getNode(index);
		return tmp == null ? null : tmp.element;
	}
	
	
	public void remove(int index) {
		Node tmp = getNode(index);
		Node up = tmp.previous;
		Node down = tmp.next;
		if (tmp != null) {
			if (up != null) {
				up.next = down;
			}
			if (down != null) {
				down.previous = up;
			} 
			// 被删元素是第一个时
			if(index == 0) {
				first = down;
			}
			// 被删元素是最后一个时
			if(index == size - 1) {
				last = up;
			}
			
			size--;
		}
	}
	
	public Node getNode(int index) {
		Node tmp = null;
		/*索引位置为前半部分，从头部开始找*/
		if (index <= size >> 1) {
			tmp = first;
			for (int i = 0; i < index; i++) {
				tmp = tmp.next;
			} 
		}else {
			/*索引位置为或半部分，从未部开始找*/
			tmp = last;
			for (int i = size -1; i > index; i--) {
				tmp = tmp.previous;
			}
		}
		
		return tmp;
	}
	
	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder("[");
		Node tmp = first;
		while(tmp != null) {
			sb.append(tmp.element + ",");
			tmp = tmp.next;
		}
		sb.setCharAt(sb.length() - 1, ']');
		return sb.toString();
	}
	
	public static void main(String[] args) {
		MyLinkedList3 list = new MyLinkedList3();
		list.add("a");
		list.add("b");
		list.add("c");
		list.add("d");
		list.add("e");
		list.add("f");
		
		System.out.println(list);
		list.remove(2);
		System.out.println(list);
		list.remove(0);// 删除第一个元素
		System.out.println(list);
		list.remove(3);// 删除最后一个元素
		System.out.println(list);
	}
}

测试：

版本四：插入节点

package com.xzlf.collection;

/**
 * 自定义一个链表
 * 插入节点
 * @author xzlf
 *
 */
public class MyLinkedList4 {
	private Node first;
	private Node last;
	private int size;
	
	public void add(Object obj) {
		Node node = new Node(obj);
		
		if(first == null) {
			first = node;
			last = node;
		}else {
			node.previous = last;
			node.next = null;
			
			last.next = node;
			last = node;
		}
		size++;
	}
	
	
	public void add(int index, Object obj) {
		Node tmp = getNode(index);
		Node newNode = new Node(obj);
		if(tmp != null) {
			Node up = tmp.previous;
			up.next = newNode;
			newNode.previous = up;
			
			newNode.next = tmp;
			tmp.previous = newNode;
			
			
		}
	}
	
	public Object get(int index) {
		Node tmp = null;
		// 判断索引是否合法
		if(index < 0 || index > size - 1) {
			throw new RuntimeException("索引不合法：" + index);
		}
		tmp = getNode(index);
		return tmp == null ? null : tmp.element;
	}
	
	
	public void remove(int index) {
		Node tmp = getNode(index);
		Node up = tmp.previous;
		Node down = tmp.next;
		if (tmp != null) {
			if (up != null) {
				up.next = down;
			}
			if (down != null) {
				down.previous = up;
			} 
			// 被删元素是第一个时
			if(index == 0) {
				first = down;
			}
			// 被删元素是最后一个时
			if(index == size - 1) {
				last = up;
			}
			
			size--;
		}
	}
	
	public Node getNode(int index) {
		Node tmp = null;
		/*索引位置为前半部分，从头部开始找*/
		if (index <= size >> 1) {
			tmp = first;
			for (int i = 0; i < index; i++) {
				tmp = tmp.next;
			} 
		}else {
			/*索引位置为或半部分，从未部开始找*/
			tmp = last;
			for (int i = size -1; i > index; i--) {
				tmp = tmp.previous;
			}
		}
		
		return tmp;
	}
	
	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder("[");
		Node tmp = first;
		while(tmp != null) {
			sb.append(tmp.element + ",");
			tmp = tmp.next;
		}
		sb.setCharAt(sb.length() - 1, ']');
		return sb.toString();
	}
	
	public static void main(String[] args) {
		MyLinkedList4 list = new MyLinkedList4();
		list.add("a");
		list.add("b");
		list.add("c");
		list.add("d");
		list.add("e");
		list.add("f");
		
		System.out.println(list);
		list.add(1, "hello");
		System.out.println(list);
	}
}

测试：

版本五：增加泛型，小的封装

package com.xzlf.collection;

/**
 * 自定义一个链表
 * 增加泛型，小的封装
 * @author xzlf
 *
 */
public class MyLinkedList5<E> {
	private Node first;
	private Node last;
	private int size;
	
	public void add(E element) {
		Node node = new Node(element);
		
		if(first == null) {
			first = node;
			last = node;
		}else {
			node.previous = last;
			node.next = null;
			
			last.next = node;
			last = node;
		}
		size++;
	}
	
	
	public void add(int index, E element) {
		checkRange(index);
		Node tmp = getNode(index);
		Node newNode = new Node(element);
		if(tmp != null) {
			Node up = tmp.previous;
			up.next = newNode;
			newNode.previous = up;
			
			newNode.next = tmp;
			tmp.previous = newNode;
			
			size++;
		}
	}
	
	private void checkRange(int index) {
		if(index < 0 || index > size - 1) {
			throw new RuntimeException("索引不合法：" + index);
		}
	}
	
	public E get(int index) {
		Node tmp = null;
		// 判断索引是否合法
		checkRange(index);
		tmp = getNode(index);
		return tmp == null ? null : (E) tmp.element;
	}
	
	
	public void remove(int index) {
		checkRange(index);
		Node tmp = getNode(index);
		Node up = tmp.previous;
		Node down = tmp.next;
		if (tmp != null) {
			if (up != null) {
				up.next = down;
			}
			if (down != null) {
				down.previous = up;
			} 
			// 被删元素是第一个时
			if(index == 0) {
				first = down;
			}
			// 被删元素是最后一个时
			if(index == size - 1) {
				last = up;
			}
			
			size--;
		}
	}
	
	private Node getNode(int index) {
		checkRange(index);
		Node tmp = null;
		/*索引位置为前半部分，从头部开始找*/
		if (index <= size >> 1) {
			tmp = first;
			for (int i = 0; i < index; i++) {
				tmp = tmp.next;
			} 
		}else {
			/*索引位置为或半部分，从未部开始找*/
			tmp = last;
			for (int i = size -1; i > index; i--) {
				tmp = tmp.previous;
			}
		}
		
		return tmp;
	}
	
	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder("[");
		Node tmp = first;
		while(tmp != null) {
			sb.append(tmp.element + ",");
			tmp = tmp.next;
		}
		sb.setCharAt(sb.length() - 1, ']');
		return sb.toString();
	}
	
	public static void main(String[] args) {
		MyLinkedList5<String> list = new MyLinkedList5<>();
		list.add("a");
		list.add("b");
		list.add("c");
		
		System.out.println(list);
		list.add(1, "hello");
		System.out.println(list);
		
		System.out.println(list.get(1));
	}
}

测试：
现在我们在编辑上使用add（） 方法后已经提示要插入String类型的数据了：

以上代码测试运行结果：

以上代码可能还有部分细节上的bug,不过作为理解LinkedList数据结构的练习应该够用了。