Java（15）ArrayList

package list;

import java.util.*;


public class MyArrayList implements List {
    
    private Object[] elementData;
    
    private int size;
    private final static int defaultCapacity = 10;

    public MyArrayList() {
        this(defaultCapacity);
    }

    public MyArrayList(int initialCapacity) {
        this.elementData = new Object[initialCapacity];
    }

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

    @Override
    public boolean isEmpty() {
        return false;
    }

    @Override
    public boolean contains(Object o) {
        return false;
    }

    @Override
    public Iterator iterator() {
        return null;
    }

    @Override
    public Object[] toArray() {
        return new Object[0];
    }

    @Override
    public boolean add(Object o) {
        // 确保存储空间能够存储新的数据
        ensureCapacity(size + 1);
        int oldSize = this.size;
        elementData[size++] = o;
        if (this.size > oldSize) {
            return true;
        }
        return false;
    }

    private void ensureCapacity(int minCapacity) {
        if (minCapacity == elementData.length) {
            int oldCapacity = elementData.length;
            // 新数组长度为原数组长度的1.5倍
            // oldCapacity >> 1 理解成 oldCapacity/2 新数组的长度是原来长度1.5倍
            int newCapacity = oldCapacity + (oldCapacity >> 1);
            // 使用传入的值和原数组1.5的最大值作为新数组的长度
            newCapacity = Math.max(minCapacity, newCapacity);
            // 空间不够数组扩容
            elementData = Arrays.copyOf(elementData, newCapacity);
        }
    }

    @Override
    public boolean remove(Object o) {
        return false;
    }

    @Override
    public boolean addAll(Collection c) {
        return false;
    }

    @Override
    public boolean addAll(int index, Collection c) {
        return false;
    }

    @Override
    public void clear() {

    }

    @Override
    public Object get(int index) {
        return elementData[index];
    }

    @Override
    public Object set(int index, Object element) {
        elementData[index] = element;
        return element;
    }

    @Override
    public void add(int index, Object element) {

    }

    @Override
    public Object remove(int index) {
        System.arraycopy(elementData, index + 1, elementData, index, size - index - 1);
        elementData[--size] = null;
        return elementData[index];
    }

    @Override
    public int indexOf(Object o) {
        return 0;
    }

    @Override
    public int lastIndexOf(Object o) {
        return 0;
    }

    @Override
    public ListIterator listIterator() {
        return null;
    }

    @Override
    public ListIterator listIterator(int index) {
        return null;
    }

    @Override
    public List subList(int fromIndex, int toIndex) {
        return null;
    }

    @Override
    public boolean retainAll(Collection c) {
        return false;
    }

    @Override
    public boolean removeAll(Collection c) {
        return false;
    }

    @Override
    public boolean containsAll(Collection c) {
        return false;
    }

    @Override
    public Object[] toArray(Object[] a) {
        return new Object[0];
    }

    @Override
    public String toString() {
        String result = "[";
        for (int i = 0; i < size; i++) {
            if (i < size - 1) {
                result += elementData[i] + ", ";
            } else {
                result += elementData[i];
            }
        }
        result += "]";
        return result;
    }
}

package Test.list;

import list.MyArrayList;
import org.junit.jupiter.api.Test;

import java.util.List;

class MyArrayListTest {
    @Test
    public void test01() {
        List list = new MyArrayList();
        for (int i = 0; i < 5; i++) {
            list.add(i);
        }
        System.out.println(list.size());
    }
//5
    @Test
    public void test02() {
        List list = new MyArrayList();
        for (int i = 0; i < 10; i++) {
            list.add(i);
        }
        System.out.println(list.size());
    }
//10
    @Test
    public void test03() {
        List list = new MyArrayList();
        for (int i = 0; i < 10; i++) {
            list.add(i);
        }
        System.out.println(list.size());
        list.add(10);
        System.out.println(list.size());
    }

    @Test
    public void test04() {
        List list = new MyArrayList();
        for (int i = 0; i < 10; i++) {
            list.add(i);
        }
        System.out.println(list.size());
        list.add(10);
        System.out.println(list.size());
        System.out.println(list.get(5));
    }

    @Test
    public void test05() {
        List list = new MyArrayList();
        for (int i = 0; i < 10; i++) {
            list.add(i);
        }
        for (int i = 0; i < list.size(); i++) {
            System.out.println(list.get(i));
        }
    }

    @Test
    public void test06() {
        List list = new MyArrayList();
        for (int i = 0; i < 10; i++) {
            list.add(i);
        }
        System.out.println(list);
    }
//[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
    @Test
    public void test07() {
        List list = new MyArrayList();
        for (int i = 0; i < 10; i++) {
            list.add(i);
        }
        System.out.println(list);
        list.remove(3);
        System.out.println(list);
        System.out.println(list.size());
    }

}