Java动态数组

package generics;

import java.util.Arrays;

// 泛型类 -> 动态数组
public class DynamicArray<E>{
    // field 
    private static final int DEFAULT_CAPACITY = 10;
    private int size;
    private Object[] elementData;
    // constructor 构造函数
    public DynamicArray(){
        this.elementData = new Object[DEFAULT_CAPACITY];
    }
    // method 
    // 确保数组有足够的长度
    private void ensureCapacity(int minCapacity){
        int oldCapacity = elementData.length;
        if(oldCapacity >= minCapacity){
            return;
        }
        int newCapacity = oldCapacity * 2;
        if(newCapacity < minCapacity){
            newCapacity = minCapacity;
        }
        elementData = Arrays.copyOf(elementData, newCapacity);
    }
    // 添加元素
    public void add(E e){
        ensureCapacity(size + 1);
        elementData[size++] = e;
    }
    // 搜索索引
    public E get(int index){
        return (E)elementData[index];
    }
    // 返回大小
    public int size(){
        return size;
    }
    // 设置元素
    public E set(int index, E element){
        E oldValue = get(index);
        elementData[index] = element;
        return oldValue;
    }
    // 泛型方法
    // 类型参数为T，放在返回类型前面
    public static <T> int indexOf(T[] arr, T elm){
        for(int i = 0; i < arr.length; i++){
            if(arr[i].equals(elm)){
                return i;
            }
        }
        return -1;
    }
    // 通配符 ?
    // <? extends E> -> 有限通配符，匹配E或E的某个子类型，用于实例化类型参数，未知具体类型
    public void addAllWailcard(DynamicArray<? extends E> c){
        for(int i = 0; i < c.size; i++){
            add(c.get(i));
        }
    }
    // <T extends E> -> 用于定义类型参数，声明一个类型参数T，可放在泛型类定义中类名的后面、泛型方法返回值前面
    public <T extends E> void addAll(DynamicArray<T> c){
        for(int i = 0; i < c.size; i++){
            add(c.get(i));
        }
    }
    // <? super E> -> 超类型通配符，可以更灵活地写入
    public void copyTo(DynamicArray<? super E> dest){
        for(int i = 0; i < size; i++){
            dest.add(get(i));
        }
    }
    @Override
    public String toString(){
        return Arrays.toString(elementData);
    }
    // __main__
    public static void main(String[] args){
        DynamicArray<String> da = new DynamicArray<String>();
        da.add("Hello");
        da.add("Hola");
        da.add("你好");
        System.out.println(da.get(2));
        System.out.println(da.size());
        System.out.println(da.set(1, "konnichiwa"));
        System.out.println(da.get(1));

        System.out.println(indexOf(new Integer[]{1, 3, 4} , 1));
        System.out.println(indexOf(new String[]{"Hello", "Hola", "你好"} , "hola"));
        System.out.println(indexOf(da.elementData, "你好"));

        System.out.println(da.toString());
        DynamicArray added = new DynamicArray();
        added.add("Hola");
        added.add("Aniaseyou");
        da.addAllWailcard(added);
        System.out.println(da.toString());
        da.addAll(added);
        System.out.println(da.toString());

        DynamicArray<Integer> ints = new DynamicArray<Integer>();
        ints.add(100);
        ints.add(34);
        DynamicArray<Number> nums = new DynamicArray<Number>();
        ints.copyTo(nums);
        System.out.println(ints.toString());
        System.out.println(nums);
    }
}