在 try 块中声明的 finally 块中关闭 Scanner/PrintStream

Question

我试图在 finally 块中关闭 Scanner 和 PrintStream，它们在 try 块中声明。问题是，如果 try-block 由于异常而失败，则永远不会声明 Scanner 和 Printstream，从而导致 finally-block 中出现错误，我想在其中关闭它们。这是代码：

        try {
            File readFile = new File(readFileName);
            File writeFile = new File(writeFileName);
            Scanner fileScanner = new Scanner(readFile);
            PrintStream output = new PrintStream(new FileOutputStream(writeFile,false)); // overwrite
            while(fileScanner.hasNextLine()) {
                output.println(fileScanner.nextLine());
                if (!fileScanner.hasNextLine()) {
                    break;
                }
                output.println();
            }
        }
        
        catch (FileNotFoundException fnfe) {
            System.out.println(fnfe.getMessage());
            System.exit(0);
        }
        
        finally {
            fileScanner.close();
            output.close();
        }

编辑：感谢您的回答，我通过在 try 块之前声明 Scanner 和 Printstream 然后在 try 中初始化它们来解决它而无需 try-with-resources -块，像这样：

Scanner fileScanner = null;
PrintStream output = null;
        try {
            fileScanner = new Scanner(readFile);
            output = new PrintStream(new FileOutputStream(writeFile,false));
            ...
        }

Answer 1

您可以使用 try-with-resources 构造：

File readFile = new File(readFileName);
File writeFile = new File(writeFileName);

try (Scanner fileScanner = new Scanner(readFile); PrintStream output = new PrintStream(new FileOutputStream(writeFile,false))) {

    while(fileScanner.hasNextLine()) {
        output.println(fileScanner.nextLine());
        if (!fileScanner.hasNextLine()) {
            break;
        }
        output.println();
    }

} catch (FileNotFoundException fnfe) {
    System.out.println(fnfe.getMessage());
    System.exit(0);
}

由于Scanner和PrintStream都实现了Autocloseable接口，它们将在异常或执行try块

后自动关闭

在 try 块中声明的 finally 块中关闭 Scanner/PrintStream

Closing Scanner/PrintStream in finally-block which are declared in try-block

java

try-catch-finally

printstream