Collection接口实现类的addAll()/removeAll()方法出现java.lang.NullPointerException

阿里巴巴Java开发手册提示：在使用Collection接口任何实现类的addAll()方法时，都要对输入的集合参数进行NPE判断。

package com.cn.demo;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class ListTest {

	public static void main(String[] args) {
		
		//初始化一个集合
		List<String> list = new ArrayList<String>(Arrays.asList("alpha", "beta", "gamma", "delta"));
		
		//1. addAll()测试
		//1.1 初始化多种情形的集合
		List<String> addList = null;
		List<String> addList1 = new ArrayList<String>();
		List<String> addList2 = new ArrayList<String>(Arrays.asList("epsilon", "zeta", "eta"));
		List<String> addList3 = new ArrayList<String>(Arrays.asList(null, "epsilon", "zeta", "eta"));
		//1.2 测试
		list.addAll(addList);//addList为null，报空指针
		list.addAll(addList1);//addList1为[]，不报错
		list.addAll(addList2);//addList2无null，不报错
		list.addAll(addList3);//addList3有null，不报错
		
		//2. removeAll()测试
		//2.1 初始化多种情形的集合
		List<String> removeList = null;
		List<String> removeList1 = new ArrayList<String>();
		List<String> removeList2 = new ArrayList<String>(Arrays.asList("alpha", "beta"));
		List<String> removeList3 = new ArrayList<String>(Arrays.asList(null, "alpha", "beta"));
		//2.2 测试
		list.removeAll(removeList);//removeList为null，报空指针
		list.removeAll(removeList1);//removeList1为[]，不报错
		list.removeAll(removeList2);//removeList2无null，不报错
		list.removeAll(removeList3);//removeList3有null，不报错
		
		System.out.println("addAll/removeAll测试：list="+list);
	}

}