自己实现ArrayList与LinkedList类

ArrayList与LinkedList的底层实现

• ArrayList内部由数组实现，LinkedList内部由链表实现。

• 自己动手实现ArrayList与LinkedList中一些常用方法

  • ArrayList的实现

import java.util.Date;

public class SxArrayList {
	
	private Object[] elementDate;
	
	private int size;
	
	public SxArrayList() {
		this(10);
	}
	
	public boolean isEmpty() {
		return size == 0;
	}
	
	
	public SxArrayList(int initalCapacity) {
		if(initalCapacity < 0) {
			try {
				throw new Exception();
			} catch (Exception e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		elementDate = new Object[initalCapacity];
	}
	
	public int size() {
		return size;
	}
	public void add(Object obj) {
		//数组扩容
		if(size+1 > elementDate.length) {
			//申请新数组
			Object[] newArray = new Object[size*2];
			//将老数组内容拷贝
			System.arraycopy(elementDate, 0, newArray, 0, elementDate.length);
			elementDate = newArray;
		}
		elementDate[size++] = obj;
	}
	
	public Object get(int index) {
		if(index < 0 || index >= size) {
			try {
				throw new Exception();
			} catch (Exception e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		return elementDate[index];
	}
	
	public void remove(int index) {
		//删除指定位置的对象
		int numMoved = size - index -1;
		if(numMoved > 0) {
			System.arraycopy(elementDate, index+1, elementDate, index, numMoved);
		}
		elementDate[--size] = null;
	}
	
	public static void main(String[] args) {
		SxArrayList list =  new SxArrayList(3);
		list.add("edasd");
		list.add(232);
		list.add(new Date());
		list.add(456);
		System.out.println(list.size());
		System.out.println(list.get(3));
		System.out.println(list.get(4)); //下标越界，抛出异常
		
	}
}

注意：在查找元素时，ArrayList内部通过equals方法实现。

LinkedList的实现

由于LinkedList由链表实现，链表由节点构成，所以把节点单独定义成一个类

//用来表示一个节点
public class Node{
	 Node previous;
	 Object obj;
	 Node next;
	
	public Node() {
		
	}

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

	public Node getPrevious() {
		return previous;
	}

	public void setPrevious(Node previous) {
		this.previous = previous;
	}

	public Object getObj() {
		return obj;
	}

	public void setObj(Object obj) {
		this.obj = obj;
	}

	public Node getNext() {
		return next;
	}

	public void setNext(Node next) {
		this.next = next;
	}

}

通过节点类构造链表，并实现常用方法

/**
 * 实现LinkedList
 *
 */
public class SxLinkedList {
	private Node first;
	private Node last;
	
	private int size;
	
	public void add(Object obj) {
		Node n = new Node();
		if(first == null) {
			//Node n = new Node();
			n.setPrevious(null);
			n.setObj(obj);
			n.setNext(null);
			
			first = n;
			last = n;
		}else {
			//直接加到last后面
			n.setPrevious(last);
			n.setObj(obj);
			n.setNext(null);
			
			last.setNext(n);
			
			last = n;
		}
		size ++;
	}
	
	public int size() {
		return size;
	}
	
	public Object get(int index) {
	
			Node temp = first;
			for(int i = 0;i < index; i++) {
				temp = temp.next;
			}
			return temp.obj;
		
	}
	
	public static void main(String[] args) {
		SxLinkedList list = new SxLinkedList();
		list.add("aaa");
		list.add(123);
		System.out.println(list.size());
		
	}
}