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