【Java】シーケンスチェーンの挿入、削除、検索、拡張の問題

## List.java
public interface List {
    //   
    boolean add(int element);

    //        index    
    boolean add(int index, int element);

    int get(int index);

    int set(int index, int val);

    //          
    int remove(int index);

    int size();

    boolean isEmpty();
    
}
## Main.java
public class Main {
    private static void test(List list) {
        list.add(1);
        list.add(2);
        list.add(3);
        list.add(4);
        System.out.println(list.get(2));
        System.out.println(list);
        list.set(2, 100);
        System.out.println(list);
        System.out.println(list.size());
        System.out.println(list.isEmpty());
        list.remove(0);
        list.remove(2);
        list.remove(0);
        list.remove(0);
        System.out.println(list);
        System.out.println(list.size());
        System.out.println(list.isEmpty());
    }

    public static void main(String[] args) {
        ArrayList arrayList = new ArrayList();
        test(arrayList);
    }
}
## ArrayList.java
import java.util.Arrays;

public class ArrayList implements List{
    int[] array=null;
    int size=0;
    public void ensureCapicity(){//    
        if(array!=null&&size<array.length){
            return;
        }
        int capacity=0;
        if(array==null){
            capacity=10;
        }
        else{
            capacity=capacity+capacity/2;
        }
        if(array!=null){
            array= Arrays.copyOf(array,capacity);
        }
        else{
            array=new int[capacity];
        }

    }

    @Override
    public boolean add(int element) {
        return add(size,element);
    }

    @Override
    public boolean add(int index, int element) {
        if(index<0||index>size){
            System.out.println("    ");
            return false;
        }
        ensureCapicity();
        System.arraycopy(array,index,array,index+1,size-index);
        array[index]=element;
        size++;
        return true;
    }

    @Override
    public int get(int index) {
        if (index < 0 || index >= size) {
            System.out.println("    ");
            return 0;
        }
        return array[index];
    }

    @Override
    public int set(int index, int val) {
        if (index < 0 || index >= size) {
            System.out.println("    ");
            return -1;
        }
        int oldval=array[index];
        array[index]=val;
        return oldval;
    }

    @Override
    public int remove(int index) {
        if (index < 0 || index >= size) {
            System.out.println("    ");
            return -1;
        }
        int oldval = array[index];
        System.arraycopy(array, index + 1, array, index, size - index - 1);
        size--;
        return oldval;
    }

    @Override
    public int size() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return size==0;
    }

    public String toString(){
        return Arrays.toString(Arrays.copyOf(array,size));
    }
}