「JavaSE 從新出發」05.03.03 使用反射編寫泛型數組代碼

Employee[] a = new Employee[100];
// ...
// array is full
a = Arrays.copyOf(a, 2 * a.length);

如何編寫這樣一個通用的 copyOf 方法呢？

// 不夠好的實現
public static Object[] badCopyOf(Object[] a, int newLength){
    Object[] newArray = new Object[newLength];
    System.arraycopy(a, 0, newArray, 0, Math.min(a.length, newLength));
    return newArray;
}
// 好的實現
public static Object goodCopyOf(Object a, int newLength){ // 聲明爲 Object 而不是 Object[] 好處：能夠擴展任意類型數組，例如 int[]
    Class cl = a.getClass();
    if(!cl.isArray()) return null;
    Class componentType = cl.getComponentType();
    int length = Array.getLength(a);
    Object newArray = Array.newInstance(componentType, newLength);
    System.arraycopy(a, 0, newArray, 0, Math.min(a.length, newLength));
    return newArray;
}