java中对于数组的扩充，使用了反射机制

简介

java中对于数组的扩充，使用了反射机制

code

package com;

import java.lang.reflect.Array;
import java.util.Arrays;

public class CopyOfTest {
	public static void main(String[] args){
		int[] a = {1, 2, 3};
		a = (int []) goodCopyOf(a, 10);
		System.out.println(Arrays.toString(a));
		
		String[] b = {"Tom", "Dick", "Harry"};
		b = (String[]) goodCopyOf(b, 10);
		System.out.println(Arrays.toString(b));
		
		System.out.println("The following call will generate an exception");
		b = (String[]) badCopyOf(b, 10);
	}
	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;
	}
	
	public static Object goodCopyOf(Object a, int newLength) {
		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(length, newLength));
		return newArray;
	}
}

自问自答

QU: badCopyOf 和 goodCopyOf 的核心区别
AN: 一个返回的是Object[] 一个返回的是 Object。一个不可以强制类型转换， 一个可以类型转换。