public class ArrayList {
    /*通过数组模拟ArrayList结构，完成容器的创建、添加、修改、删除，以及可以
遍历自定义的结构，提示可以ArrayList源码。
*/
    int n=2;
    int size=-1;
    Object []array;
    public ArrayList(){
        array=new Object[n];
    }
    public static void main(String[] args) {
        ArrayList arrayList=new ArrayList();
        arrayList.add("f");
        arrayList.add("a");
        arrayList.add("w");
        for (int i = 0; i <arrayList.size+1 ; i++) {
            System.out.println(arrayList.getarray(i));
        }
        System.out.println("------------");
        arrayList.add(2, "2");
//        越界，报错
        arrayList.add(5, "5");

        for (int i = 0; i <arrayList.size ; i++) {
            System.out.println(arrayList.getarray(i));
        }
        System.out.println("--------------");
        arrayList.remove(2);
        arrayList.remove("f");
        for (int i = 0; i <arrayList.size ; i++) {
            System.out.println(arrayList.getarray(i));
        }
        arrayList.set(1, "10");
        System.out.println("--------------");
        for (int i = 0; i <arrayList.size ; i++) {
            System.out.println(arrayList.getarray(i));
        }
    }
    public void enlarge(){
        n=n*2+1;
        Object [] newarray=new Object[n];
        System.arraycopy(array, 0, newarray, 0, array.length);
        array=newarray;

    }
    public Object getarray(int i){
        return array[i];
    }
    public int add(int index,Object obj){
        if(index>n-1){
            enlarge();
        }
        if(index>size&&index<n){
            System.out.println("java.lang.IndexOutOfBoundsException");
        }
        for (int i=index; i <=size; i++) {
            array[index+1]=array[index];
        }
        array[index]=obj;
        size++;
        return size;
    }
    public int add(Object obj){
        if(size>=n-1){
            enlarge();
        }
        array[size+1]=obj;
        size++;
        return size;
    }
    public void remove(int index){
        for (int i = index; i<size; i++) {
            array[i]=array[i+1];
        }
        array[size]=null;
        size--;
    }
    public void remove(Object obj){
        for (int i = 0; i <=size ; i++) {
            if(obj.equals(getarray(i))==true){
                remove(i);
            }
        }
    }
    public void set(int index,Object obj){
        array[index]=obj;
    }