自己实现ArrayList

使用泛型自己实现了ArrayList，功能都差不多，只是构造函数初始化的时候有差别。

ArrayList源代码内部是使用Object[]来保存你add的对象的，然后在你get的时候再强制转换一下。本文是直接申请的模板类型的数组T[]。因此在调用构造函数时需要将类的类型也传入，详见代码。

</pre><pre name="code" class="java">package tools;

import java.lang.reflect.Array;
import java.util.Iterator;

public class MyArrayList<T> implements Iterable<T> {

	private int size;
	private int cap;
	private T[] array;
	private Class<T> type;
	
	public MyArrayList(Class<T> type, int cap){
		this.type = type;
		this.size = 0;
		this.cap = cap;
	}
	
	public MyArrayList(Class<T> type){
		this.type = type;
		this.size = 0;
		this.cap = 128;
		this.array = (T[]) Array.newInstance(type, this.cap);
	}
	
	private void lager(){
		T[] temp = (T[]) Array.newInstance(this.type, this.cap*2);
		for(int i = 0; i < this.cap; ++i){
			temp[i] = this.array[i];
		}
		this.array = temp;
		this.cap = this.cap * 2;
	}
	
	public void add(T obj){
		if(size==cap){
			lager();
		}
		this.array[size++]=obj;
	}
	
	public T get(int index){
		if(index < this.size){
			return this.array[index];
		}
		return null;
	}
	
	public T remove(int index){
		if(index < this.size){
			T temp = this.array[index];
			for(int i = index; i < this.size-1; ++ i){
				this.array[i] = this.array[i+1];
			}
			this.size-=1;
			return temp;
		}
		return null;
	}
	
	public int getSize(){
		return this.size;
	}

	@Override
	public Iterator<T> iterator() {
		// TODO Auto-generated method stub
		return new ALIterator();
	}
	
	class ALIterator implements Iterator<T>{
		private int _index;
		@Override
		public boolean hasNext() {
			// TODO Auto-generated method stub
			return _index != size;
		}

		@Override
		public T next() {
			// TODO Auto-generated method stub
			return array[_index ++];
		}
		
	}
}

测试代码：

package tools;

import java.util.ArrayList;
import java.util.List;

public class ArrayListTest {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		MyArrayList<A> array = new MyArrayList<A>(A.class, 2);
		array.add(new A(1));
		System.out.println(array.getSize());
		array.add(new A(2));
		array.add(new A(3));
		System.out.println(array.getSize());
		
		for(A i : array){
			i.print();
		}
	}
}

class A{
	private int id;
	public A(int id){
		this.id = id;
	}
	public void print(){
		System.out.println("A.class " + this.id);
	}
}