try-finally 语句是保证资源正确关闭的最佳方式，但是当添加多个资源时，情况会变糟

// try-finally is ugly when used with more than one resource!
static void copy(String src, String dst) throws IOException {InputStream in = new FileInputStream(src);try {OutputStream out = new FileOutputStream(dst);try {byte[] buf = new byte[BUFFER_SIZE];int n;while ((n = in.read(buf)) >= 0)out.write(buf, 0, n);} finally {out.close();}} finally {in.close();}
}

        当 Java 7 引入了 try-with-resources 语句时，所有这些问题一下子都得到了解决。要使用这个构造，资源必须实现 AutoCloseable 接口

// try-with-resources on multiple resources - short and sweet
static void copy(String src, String dst) throws IOException {try (InputStream in = new FileInputStream(src);OutputStream out = new FileOutputStream(dst)) {byte[] buf = new byte[BUFFER_SIZE];int n;while ((n = in.read(buf)) >= 0)out.write(buf, 0, n);}
}

try-with-resources 语句中添加 catch 子句，就像在常规的 try-finally 语句中一样

// try-with-resources with a catch clause
static String firstLineOfFile(String path, String defaultVal) {try (BufferedReader br = new BufferedReader(new FileReader(path))) {return br.readLine();} catch (IOException e) {return defaultVal;}
}