java - 绕过 'Cannot refer to a non-final variable inside an inner class defined'

Question

我有以下代码，但是当我在新的 Thread 类之外声明 String 行时，我得到了一个异常。我来自 C# 背景，所以我现在明白 Java 不支持真正的闭包。所以我的问题是:

如何在新线程之外声明一个字符串并在新线程中使用它？

Cannot refer to a non-final variable line inside an inner class defined in a different method

ProcessBuilder builder =
    new ProcessBuilder("/Users/Joe/Desktop/file", "-i", src);
builder.redirectErrorStream(true);
Process process = builder.start();
final InputStream is = process.getInputStream();
String line;
new Thread(new Runnable() {
    @Override public void run() {
        try {
            BufferedReader br = new BufferedReader(new InputStreamReader(is));
            while ((br.readLine()) != null) {
                line += br.readLine() + "\n";
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }               
}).start();

Answer 1

将 line 更改为 StringBuilder 并将其声明为 final。然后更改 run() 方法以附加到 StringBuilder。

假设您在尝试读取主线程中的行之前join()子线程，则不需要使用StringBuffer.