模拟ArrayList

最近公司没什么项目，闲来无事，写了段代码，模拟下ArrayList，代码如下：

  package com.test;

public class ImitateArrayList<T> {
    //定义一个默认的容器大小
	private static final int DEFAULT_CAPACITY = 16;

	//存放数据的数组
	private Object[] elements;

	//元素的数量和指向数组的下一个索引
	private int size;  

	public ImitateArrayList(){
		this(DEFAULT_CAPACITY);
	}

	public ImitateArrayList(int capacity){
		if(capacity < 0){
			throw new IllegalArgumentException("invalid capacity "+ capacity);
		}
		elements = new Object[capacity];
	}


	/*
	 * 向容器中添加元素
	 */
	public void addElement(T obj){


		if(checkCapacity()){
			ensurceCapacity(); 
		}
		elements[size++] = obj;
	}







	/*
	 * 增加数组的容量
	 */
   private void ensurceCapacity(){
	   int oldCapacity = elements.length;
	   int newCapacity = oldCapacity * 3 / 2;
	   Object[] oldData = elements;
	   elements = new Object[newCapacity];
	   System.arraycopy(oldData,0,elements,0,size);
   }

   /*
    * 返回容器中元素的个数
    */
   public int size(){
	   return size;
   }

    @Override
    public String toString() {

       StringBuilder stringBuilder = new StringBuilder(100);
       stringBuilder.append("[");
       for(int i = 0; i < size;i++){

    	   if(i == size - 1){
    		   stringBuilder.append(elements[i].toString());
    	   }else{
    		   stringBuilder.append(elements[i].toString() + ",");  
    	   }
       }

       stringBuilder.append("]");
       return  stringBuilder.toString();   
    }

    public Object remove(int index){

    	checkIndex(index);  
    	Object oldElement = elements[index];  
    	moveElement(index,Operation.REMOVE);
    	size--;
    	return oldElement;

    }


    //检验索引

    private void checkIndex(int index){
     	if(index >= size || index < 0){
    		throw new IllegalArgumentException("invalid argument "+index);
    	}
    }

	//移动元素
    private void moveElement(int index,Operation operation) {
	  	if(operation  == Operation.REMOVE ){
	  		for(int i = index; i < size - 1;i++){
	  	  	  elements[i] = elements[i + 1];  	
	  	  	}
	  	  }else if(operation == Operation.ADD){
	  		for(int i = elements.length - 2; i >= index ;i--){
		  	  	  elements[i + 1] = elements[i];	
		  	  	}
	  	  }


	}


    //获取数组中的一个元素

    public T get(int index){
    	this.checkIndex(index);
    	return (T)elements[index];
    }

    //在固定的索引位置插入一个元素
    public void add(int index,T element){

    	//是否要增加容量
    	if(checkCapacity()){
    		ensurceCapacity();
    	}

    	//检查index
        if(index < 0 || index >= elements.length){
        	throw new IllegalArgumentException("invalid index "+ index);
        }
        //如果          
    	if(index >= size){
    		elements[size] = element;
    	}else{
    	  moveElement(index,Operation.ADD);
    	  elements[index] = element;
    	}

    	size++;
    }


    //检验当前的元素个数是否等于容器的容量


	private boolean checkCapacity() {
		// TODO Auto-generated method stub
		if(size >= elements.length){
			return true; 
		}
		return false;
	}


   //删除传入的某个元素

  public boolean remove(Object obj){
	  boolean isDeleted = false;
	  if(obj == null){
		  isDeleted = true;
	  }else{
		  int index = this.indexOf(obj);
		  remove(index);
		  isDeleted = true;
	  }

	  return isDeleted;   


  }

  //得到元素的索引位置

  public int indexOf(Object obj){
	  int index = -1;
      for(int i = 0;i < size;i++){
		  if(obj.equals(elements[i])){
			  index = i;
		  }
	  }

      return index;

  }




}

//iterator的实现
private class IteratorImpl implements Iterator<T>{

	private int cursor = 0;
	private int lastRef = -1;
	@Override
	public boolean hasNext() {
		// TODO Auto-generated method stub
		return cursor < size;
	}

	@Override
	public T next() {
		// TODO Auto-generated method stub
		 T next = ImitateArrayList.this.get(cursor);
		lastRef = cursor++;
		return next ;
	}

	@Override
	public void remove() {
		// TODO Auto-generated method stub
		if(lastRef == -1){
			throw new IllegalStateException("before remove you must call next() method");
		}
		ImitateArrayList.this.remove(lastRef);
		if(lastRef < cursor){
			cursor--;
		}
		lastRef = -1;
	}

  }



@Override
public Iterator<T> iterator() {
	// TODO Auto-generated method stub
	return new IteratorImpl();
}

下面是测试代码:

 package com.test;

import static org.junit.Assert.*;

import org.junit.Before;
import org.junit.Test;

public class ImitateArrayListTest {

	private ImitateArrayList<Object> imitateArrayList;

	@Before
	public void setUp(){

		imitateArrayList = new ImitateArrayList<Object>(2);
	}

	/*
	 * 测试向顺序存储列表添加元素
	 */
	@Test
	public void testAddElement() {

		imitateArrayList.addElement("abc");
		imitateArrayList.addElement("def");
		int actual = imitateArrayList.size();
		assertEquals(2,actual);
	}

	/*
	 * 测试超出容量
	 */
	@Test
	public void testExceedInitCapacity(){

		imitateArrayList.addElement("abc");
		imitateArrayList.addElement("def");
		imitateArrayList.addElement("jkl");
		imitateArrayList.addElement("kif");
		int actual = imitateArrayList.size();
		assertEquals(4,actual);
	}

	/*
	 * 测试toString
	 */

	@Test
	public void testToString(){

		imitateArrayList.addElement("abc");
		imitateArrayList.addElement("def");
		imitateArrayList.addElement("jkl");
		imitateArrayList.addElement("kif");
		String actual = imitateArrayList.toString();

		assertEquals("[abc,def,jkl,kif]",actual);

	}

	/*
	 * 测试删除一个元素
	 */
	@Test
	public void testRemove(){
		imitateArrayList.addElement("abc");
		imitateArrayList.addElement("def");
	    imitateArrayList.remove(0);
		Object actual = imitateArrayList.get(0);
		assertEquals("def",actual);

	}

	/*
	 * 测试在指定的索引位置增加一个元素
	 */
	@Test
	public void testAddSpecifyIndex(){
		imitateArrayList.add(0,"abc");
		imitateArrayList.add(0,"def");
		Object actual = imitateArrayList.get(0);
		System.out.print(imitateArrayList.toString());
		assertEquals("def",actual);
	}

	/*
	 * 测试在指定的索引位置增加一个元素
	 */
	@Test  
	public void testRemoveByObject(){
		imitateArrayList.add(0,"abc");
		imitateArrayList.add(0,"def");
		boolean actual = imitateArrayList.remove("abc");
		System.out.println(imitateArrayList.get(0));
		assertEquals(true,actual);
	}


}

只写了arrayList的部分功能