main.java

package com.company;
//import java.util.ArrayList;

public class Main {

    public static void main(String[] args) {
    // write your code here
        ArrayList list = new ArrayList();
        //list.get(-10);
        list.add(99);
        list.add(88);
        list.add(77);
        list.add(
 
66);
        list.add(55);

        //list.remove(2);
        //list.get(5);
        //list.add(list.size(),100);

        //list.set(3,80);
        System.out.println(list);





//        ArrayList list = new ArrayList(5);
//        list.add(99);
//        list.add(88);
//        list.add(77);
//        list.add(66);
 
//        list.add(55);
//        list.remove(2);
//        System.out.println(list);
    }
}

ArrayList.java

package com.company;

import java.util.Arrays;

public class ArrayList {

    private int size;

    private int[] elements;

    private static final int DEFALT_CAPACITY = 2;
    private static final
 
 int ELEMENT_NOT_FOUND = -1;

    public ArrayList(int capacity){
        capacity = (capacity < DEFALT_CAPACITY) ? DEFALT_CAPACITY : capacity;
        elements = new int[capacity];

    }

    public ArrayList(){
        //elements = new int[10];
        this(DEFALT_CAPACITY);
    }

    public int size(){
        return size;
    }

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

    /**
     * 獲取index位置的元素
     * @param index
     * @return
     */
    public int get(int index){
        if (index < 0 || index >= size){
            throw new IndexOutOfBoundsException("index不合適");
        }
        return elements[index];
    }

    /**
     * 設定index位置的元素
     * @param index
     * @param element
     * @return
     */
    public int set(int index, int element){
        if (index < 0 || index >= size){
            throw new IndexOutOfBoundsException("index不合適");
        }
        int old = elements[index];
        elements[index] = element;
        return old;
    }

    /**
     * 某個元素的下標
     * @param element
     * @return
     */
    public int indexOf(int element){
        for (int i = 0; i < size; i++){
            if (elements[i] == element)return i;
        }
        return ELEMENT_NOT_FOUND;
    }

    /**
     * 是否包含某個元素
     * @param element
     * @return
     */
    public boolean contains(int element){
        return indexOf(element) != ELEMENT_NOT_FOUND;
    }

    public void add(int element){
        //elements[size++] = element;
        ensureCapacity(size+1);
       add(size,element);
    }

    public int remove(int index){
        System.out.println(size);
        if (index < 0 || index >= size){
            throw new IndexOutOfBoundsException("index不合適");
        }
        int old = elements[index];
        for (int i = index + 1; i <= size - 1; i++){
            elements[i - 1] = elements[i];
        }
        size--;
        return old;
    }

    public void clear(){
        size = 0;
    }

    /**
     * 往index位置新增元素 注意從後往前挪動
     * @param index
     * @param element
     */
    public void add(int index,int element){
        //允許=size
        if (index < 0 || index > size){
            throw new IndexOutOfBoundsException("index不合適");
        }
        for (int i = size - 1;i >= index;i--){
            elements[i+1] = elements[i];
        }
        elements[index] = element;
        size++;
    }

    /**
     * 保證要有capacity的容量
     * @param capacity
     */
    private void ensureCapacity(int capacity){
        int oldCapacity = elements.length;
        if (oldCapacity >= capacity)return;
        //動態擴容
        int newCapacity = oldCapacity + (oldCapacity >> 1);// 右移除以2
        System.out.println(size+"動態擴容"+newCapacity);
        int[] newElements = new int[newCapacity];
        for (int i = 0; i < size; i++){
            newElements[i] = elements[i];
        }
        elements = newElements;
    }

    @Override
    public String toString() {
//這種會打印出全部位置的元素
//        return "ArrayList{" +
//                "size=" + size +
//                ", elements=" + Arrays.toString(elements) +
//                '}';

        StringBuilder string = new StringBuilder();
        string.append("size=").append(size).append(",[");
        for (int i = 0;i < size; i++){
            if (i != 0){
                string.append(",");
            }
            string.append(elements[i]);
        }
        string.append("]");
        return string.toString();


    }
}

Assert.java

package com.company;

public class Assert {
    public static void test(boolean value){
        try{
            if(!value) throw new Exception("測試不通過");
        }
        catch (Exception e){
            e.printStackTrace();
        }
    }
}