为什么我必须在创建对象时创建类型为FileReader / Writer的inputStream和outputStream？ [英] Why must I create inputStream and outputStream with type FileReader/Writer when im creating the objects themselves?

问题描述

好的这是代码，我的问题是为什么我必须把 FileReader inputstream = null; 和 FileWriter 。为什么我不能在try块中稍后创建对象？我错过了什么......我可能是。

Ok this is the code and my question is why do i have to put FileReader inputstream = null; and the same with FileWriter. Why can't I simply create the objects later in the try block? Am I missing something... I probably am.

public static void main(String[] args) throws IOException{
    // TODO Auto-generated method stub
        FileReader inputStream = null;
        FileWriter outputStream = null;
        try {
            inputStream = new FileReader("In.txt");
            outputStream = new FileWriter("Out.txt");
            int c;
            while ((c = inputStream.read()) != -1){
                outputStream.write(c);

            }
        }
                finally {
                    if (inputStream != null){
                        inputStream.close();
                    }
                    if (outputStream != null){
                        outputStream.close();

                }
        }

推荐答案

因为您无法在 finally 块中引用它们，因此您将无法关闭它们。

Because you won't be able to refer to them in the finally block, and so you won't be able to close them.

顺便说一句，如果他们是读者和作家，你最好用这种方式命名变量，而不是 xStream 。

Btw, if they are reader and writer, you'd better name the variables that way, rather than xStream.

I / O处理一直很乏味，这就是为什么Java 7引入尝试使用资源

I/O handling has always been tedious, that's why Java 7 introduced "try with resource"

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