1.     @org.junit.Test
    2.     public void test(){
    3.         //1.创建一个容器
    4.         MyArrayList list = new MyArrayList();
    6.         //2.装对象
    7.         list.add("张三");
    8.         list.add("李四");
    9.         list.add("王五");
    10.         list.add(null);     //null也合法
    11.         list.add(10);
    13.         //3.查看有几个元素
    14.         System.out.println(list.size());
    15.         System.out.println();
    17.         //4.遍历元素
    18.         Object[] objects = list.toArray();
    19.         for (int i = 0; i < objects.length; i++) {
    20.             System.out.println(objects[i]);
    21.         }
    22.         System.out.println();
    24.         //5.获取index位置的元素
    25.         Object object = list.get(0);
    26.         System.out.println(object);
    27.         System.out.println();
    29.         //6.查询李四的位置
    30.         int index = list.indexOf("李四");
    31.         System.out.println(index);
    32.         System.out.println();
    34.         //7.替换“李四”为“张康”
    35.         Object[] newObjects = list.set("李四", "张康");
    36.         for (int i = 0; i < newObjects.length; i++) {
    37.             System.out.println(newObjects[i]);
    38.         }
    39.     }
    41.     public class MyArrayList{
    43.         private Object[] data;
    45.         private int total;
    47.         public MyArrayList() {
    48.             this.data = new Object[10]; //默认初始化大小
    49.         }
    51.         //添加元素
    52.         public void add(Object obj){
    53.             //是否已满
    54.             if(total >= data.length)
    55.                 //扩容
    56.                 data = Arrays.copyOf(data, data.length*2);
    57.             data[total++] = obj;
    58.         }
    60.         //获取有效元素的个数
    61.         public int size(){
    62.             return total;
    63.         }
    65.         //把数据用数组返回
    66.         public Object[] toArray(){
    67.             return Arrays.copyOf(data, total);
    68.         }
    70.         //获取index位置的元素
    71.         public Object get(int index){
    72.             if (index < 0 || index >= total)
    73.                 throw new IndexOutOfBoundsException(index + "不合法");
    74.             return data[index];
    75.         }
    77.         //查找obj在当前容器中的索引，如果没有，返回-1
    78.         public int indexOf(Object obj){
    79.             int index = -1;
    80.             //null.equals("")会报空指针异常
    81.             //"".equals(null)不会报空指针异常
    82.             if (obj == null) {
    83.                 for (int i = 0; i < total; i++){
    84.                     if (obj == data[i]) {
    85.                         index = i;
    86.                         break;
    87.                     }
    88.                 }
    89.             } else {
    90.                 for (int i = 0; i < total; i++){
    91.                     if (obj.equals(data[i]) ) {
    92.                         index = i;
    93.                         break;
    94.                     }
    95.                 }
    96.             }
    97.             return index;
    98.         }
    100.         //删除对象
    101.         public void remove(Object obj) {
    102.             //(1)找到obj位置
    103.             int index = indexOf(obj);
    104.             //(2)删除
    105.             if (index != -1) {
    106.                 System.arraycopy(data, index+1, data, index,  total-index-1);
    107.                 data[--total] = null;
    108.             }
    109.         }
    111.         //把容器中的old替换成dest
    112.         public Object[] set(Object old, Object dest) {
    113.             int index = indexOf(old);
    114.             if (index != -1)
    115.                 data[index] = dest;
    116.             return Arrays.copyOf(data, total);
    117.         }
    118.     }