Question

我正在尝试从一个文件中读取，但我只是不知道如何在使用try catch块的时候这样做...如果发生了一些不好的事情，怎么能让它抛出异常，但如果没关系执行这一行：br.readLine（）？它只是说br没有被宣布。如果我需要在不同的地方使用“br”和“bw”（比如不同的方法）怎么办？我是否必须在那里申报？

try {
    BufferedReader br = new BufferedReader(new FileReader(file));
    BufferedWriter bw = new BufferedWriter(new FileWriter(file));
} catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

br.readLine();

Answer 1

br在try的范围内声明，因此在catch之后消失了。你想这样做：

BufferedReader br = null;
BufferedWriter bw = null;
try {
    br = new BufferedReader(new FileReader(file));
    bw = new BufferedWriter(new FileWriter(file));
} catch (IOException e) {
    e.printStackTrace();
}
br.readLine();

注意你在catch之后冒空指针的风险，所以另一个选择是将br.readLine（）写入try中，如下所示：

try {
    BufferedReader br = new BufferedReader(new FileReader(file));
    BufferedWriter bw = new BufferedWriter(new FileWriter(file));
    br.readLine();
} catch (IOException e) {
    e.printStackTrace();
}

Answer 2

BufferedReader and BufferedWriter should be define outside from try and catch block than only we can access them outside
Try this code, it should work


     BufferedReader br = null;
             BufferedWriter bw =null;
             try {
                  br = new BufferedReader(new FileReader(file));
                  bw = new BufferedWriter(new FileWriter(file));
             } catch (IOException e) {
                 // TODO Auto-generated catch block
                 e.printStackTrace();
             }
br.readLine();

Answer 3

您已在try块中声明了BufferedReader和BufferredWriter，并在try和catch之外调用了br.readline（），因此它不知道br的声明位置。我有与上面相同的答案。

try {
BufferedReader br = new BufferedReader(new FileReader(new File ("path_to_your_file_to read")));
BufferedWriter bw = new BufferedWriter(new FileWriter(new File("path_to_your_file_to_write")));
br.readLine();
} catch (IOException e) {
e.printStackTrace();
}

读/写文件时处理异常

3 个答案: