import org.omg.CORBA.PUBLIC_MEMBER;

import java.io.Serializable;
import java.util.*;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;
import java.util.stream.Stream;

public class MyArrayList<T> {
    int size;
    
 
private Object array[];
    private static final Object[] EMPTY_ARRAY={};
    public MyArrayList()
    {
        this(10);
    }
    public MyArrayList(int initCapcity) {
        if (initCapcity < 0)
            throw new IllegalArgumentException("initCapcity必須大於0");
        else if (initCapcity==0)
        {
            
 
this.array=EMPTY_ARRAY;
        }else {
            array=new Object[initCapcity];
        }

    }
    public MyArrayList(Collection<? extends T> c)
    {
        array=c.toArray();
        if((size=array.length)!=0)
        {
            if (array.getClass()!=Object[].class)
            {
                array
 
=Arrays.copyOf(array,size,Object[].class);
            }
        }else {
            this.array=EMPTY_ARRAY;
        }
    }
    public boolean isEmpty()
    {
        return size==0;
    }

    public int size() {
        return size;
    }
    public boolean add(Object obj)
    {
        ensureCapacity();
        array[size++]=obj;
        return true;
    }
    public void add(int index,Object object)
    {
        rangeCheck(index);
        ensureCapacity();
        System.arraycopy(array,index,array,index+1,size-index);
        array[index]=object;
        size++;

    }
    public Object remove(int index)
    {
        rangeCheck(index);
        Object oldObject=array[index];
        if (array.length-index-1>0)
        {
            System.arraycopy(array,index+1,array,index,array.length-index-1);
        }
        array[size--]=null;
        return oldObject;
    }
    public boolean remove(Object object)
    {
        if (object==null)
        {
            for (int i=0;i<size;i++)
            {
                if (array[i]==null)
                    remove(i);
                return true;
            }
        }else {
            for (int i=0;i<size;i++)
            {
                if (object.equals(array[i]))
                {
                    remove(i);
                    return true;
                }

            }
        }
        return  false;
    }

    public Object get(int index)
    {
        rangeCheck(index);
        return array[index];
    }
    public void set(int index,Object object)
    {
        rangeCheck(index);
        Object oldObject=array[index];
        array[index]=object;
    }
    //判斷索引是否越界
    public void rangeCheck(int index)
    {
        if (index>=size||index<0)
            throw new IndexOutOfBoundsException("索引不在範圍內");
    }


    //數組容量與size相等時進行擴容
    public void ensureCapacity()
    {
        if (size==array.length)
        {
            Object []  newArray=new Object[2*size+1];
            System.arraycopy(array,0,newArray,0,array.length);
            array=newArray;
        }
    }
}

測試類：

import java.util.ArrayList;

public class Demo1 {
    public static void main(String[] args)
    {
        MyArrayList myArrayList=new MyArrayList<String>();
        myArrayList.add("aaaaa");
        myArrayList.add("bbbbb");
        System.out.println(myArrayList.get(0));
        System.out.println(myArrayList.get(1));
        myArrayList.remove(0);
        System.out.println(myArrayList.get(0));
        myArrayList.set(0,"xujinfeng");
        System.out.println(myArrayList.get(0));
        System.out.println(myArrayList.size());
    }
}

手動實現一個簡單的ArrayList