Question

我无法编译该程序。问题出在最后一行＆＃34; out.close＆＃34;。请告诉我如何纠正它以及它导致问题的原因。

import java.io.*;

public class Test {

    public static void main(String args[]) throws IOException {
        try {
            BufferedReader in = new BufferedReader(new FileReader(args[0]));
            BufferedWriter out = new BufferedWriter(new FileWriter(args[1]));
            String line;
            line = in.readLine();
            while (line != null) {
                out.write(line, 0, line.length());
                out.newLine();
                line = in.readLine();
            }
        } finally {
            out.close();
        }
    }
}

Answer 1

你必须在try-finally块之外声明BufferedWriter out变量，因为在try块中声明的变量最终超出了范围，它被称为块作用域。代码应该是：

BufferedWriter out = null;
try {
    BufferedReader in = new BufferedReader(new FileReader(args[0]));
    out = new BufferedWriter(new FileWriter(args[1]));
    String line;
    line = in.readLine();
    while (line != null) {
        out.write(line, 0, line.length());
        out.newLine();
        line = in.readLine();
    }
} finally {
    if (out != null)
        out.close();
}

或者正如评论中所述，如果Java版本为7或更高版本，您应该使用try-with-resources：

try(BufferedReader in = new BufferedReader(new FileReader(args[0]));
    BufferedWriter out = new BufferedWriter(new FileWriter(args[1]))) 
{
    String line;
    line = in.readLine();
    while (line != null) {
        out.write(line, 0, line.length());
        out.newLine();
        line = in.readLine();
    }
}

在这种情况下，您无需在finally块中手动关闭它。

Answer 2

Try with Resources（Java 7+）。在这种情况下，不需要密切的陈述。在try中声明的资源将自动关闭。

    try(BufferedReader in = new BufferedReader(new FileReader(args[0]));
        BufferedWriter out = new BufferedWriter(new FileWriter(args[1])))
        {
        String line;
        line = in.readLine();
        while (line != null) {
            out.write(line, 0, line.length());
            out.newLine();
            line = in.readLine();
        }
    } catch (FileNotFoundException e) {
    } catch (IOException e) {
    } finally {
    }

Answer 3

您需要在yur out块之外声明您的try . . . finally变量。由于try和finally是两个不同的范围，因此out块中未定义finally。

无法关闭输出流

3 个答案: