英文:
How to initialize PrintWriter array?
问题
我必须创建 n 个文件。n 是随机的，但它将在 1<=n<=7 的范围内。当我运行这个程序时，它会出现 NullPointException（空指针异常）。file_num 是要创建的文件数量。如果我从第一行中删除 null，它会告诉我要初始化数组。
PrintWriter[] writer = null;
for (int j = 0; j < file_num; j++) {
System.out.println("J is " + j);
writer[j] = new PrintWriter(new File("file" + (j + 1) + ".csv"));
}
英文:
I have to create n number of files. N is random but it will be in this range 1<=n<=7. When I run this program it gives NullPointException. file_num is number of files to be created. If I remove null from the first line it tells me to initialize the array.
PrintWriter[] writer=null;
for(int j=0;j<file_num;j++)
{
System.out.println("J is "+j);
writer[j] =new PrintWriter(new File("file"+(j+1)+".csv"));
}
答案1
得分: 0
当我运行这个程序时，它会产生空指针异常。
这是因为
PrintWriter[] writer = null;
你应该用大小为 file_num 的新空数组初始化 writer 数组
PrintWriter[] writer = new PrintWriter[file_num];
英文:
> When I run this program it gives NullPointException.
That's because
PrintWriter[] writer = null;
You should initialize writer array with new empty array of size file_num
PrintWriter[] writer = new PrintWriter[file_num];
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