有三种不同的方式关闭输出写入器。第一种将close()语句放在try子句方法里面，第一种在try子句中放置close()方法，第二个放在finally子句中，第三个使用try-with-resources语句，哪个是最正确？

//close() is in try clause
try {
    PrintWriter out = new PrintWriter(
            new BufferedWriter(
            new FileWriter("out.txt", true)));
    out.println("the text");
    out.close();
} catch (IOException e) {
    e.printStackTrace();
}

close 放在finally里面。

//close() is in finally clause
PrintWriter out = null;
try {
    out = new PrintWriter(
        new BufferedWriter(
        new FileWriter("out.txt", true)));
    out.println("the text");
} catch (IOException e) {
    e.printStackTrace();
} finally {
    if (out != null) {
        out.close();
    }
}

//try-with-resource statement
try (PrintWriter out2 = new PrintWriter(
            new BufferedWriter(
            new FileWriter("out.txt", true)))) {
    out2.println("the text");
} catch (IOException e) {
    e.printStackTrace();
}

答案

因为Writer必须在任何情况下被关闭（异常情况或非异常情况），close()应该在finally被关闭。