正在关闭try块中声明的finally块中的Scanner/PrintStream

Question

我正在尝试关闭finally块中的Scanner和PrintStream，它们在try块中声明。问题是，如果try块由于异常而失败，则Scanner和Printstream永远不会被声明，从而导致finally块中出现错误，我想在那里关闭它们。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：谢谢你的回答，我在没有尝试资源的情况下解决了这个问题，在尝试块之前声明Scanner和Printstream，然后在尝试块中初始化它们，如下所示：

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，因此在异常或执行try块后，它们将自动关闭