什么是Java中try catch中的圆括号/圆括号（）

Question

As per as my knowledge we use try catch as follows:

try {
   //Some code that may generate exception
}
catch(Exception ex) {
}
   //handle exception
finally {
   //close any open resources etc.
}

But in a code I found following

try(
    ByteArrayOutputStream byteArrayStreamResponse  = new ByteArrayOutputStream();                   
    HSLFSlideShow   pptSlideShow = new HSLFSlideShow(
                                      new HSLFSlideShowImpl(
 Thread.currentThread().getContextClassLoader()
       .getResourceAsStream(Constants.PPT_TEMPLATE_FILE_NAME)
                                     ));
 ){
}
catch (Exception ex) {
       //handel exception
}
finally {
      //close any open resource
}

I am not able to understand why this parentheses () just after try.

What is the usage of it? Is it new in Java 1.7? What kind of syntax I can write there?

Please also refer me some API documents.

Answer 1

It is try with Resources syntax which is new in java 1.7. It is used to declare all resources which can be closed. Here is the link to official documentation. https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html

static String readFirstLineFromFile(String path) throws IOException {
try (BufferedReader br =
               new BufferedReader(new FileReader(path))) {
    return br.readLine();
}
}

In this example, the resource declared in the try-with-resources statement is a BufferedReader. The declaration statement appears within parentheses immediately after the try keyword. The class BufferedReader, in Java SE 7 and later, implements the interface java.lang.AutoCloseable. Because the BufferedReader instance is declared in a try-with-resource statement, it will be closed regardless of whether the try statement completes normally or abruptly (as a result of the method BufferedReader.readLine throwing an IOException).