Running a program consist of try block but without catch or final clauses

Question

Usually this would give syntax error. But in the oracle tutorial in try-with-resources Statement section , there are several code samples with try block but without catch or finally statements. How come this codes does not give syntax errors?

Because it was added to the language spec like that in Java 7. — Erwin Bolwidt, Jan 06 '16 at 07:21
Why do you believe they should cause a syntax error? A new syntax has new rules, is that so surprising? — Peter Lawrey, Jan 06 '16 at 07:23
The likelihood is, the method has been declared to throw the resulting exception, try-with-resources is (effectively) the same as try-finally — MadProgrammer, Jan 06 '16 at 07:23
Possible Duplicate of http://stackoverflow.com/questions/4559661/java-try-catch-finally-blocks-without-catch — Amit Jain, Jan 06 '16 at 07:26

score 5 · Accepted Answer · answered Jan 06 '16 at 07:20

5

In try with resources block, an implicit finally is added with code calling the close() method on all Closable instances...

So, a finally is still present in the block. So it's syntactically correct.

answered Jan 06 '16 at 07:20

Codebender

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@Optimuskck new as in Java 7 is so old, it isn't publicly supported ;) – Peter Lawrey Jan 06 '16 at 07:24

score 1 · Answer 2 · answered Jan 06 '16 at 11:55

The try-with-resources statement is a try statement that declares one or more resources. A resource is an object that must be closed after the program is finished with it. The try-with-resources statement ensures that each resource is closed at the end of the statement. Any object that implements java.lang.AutoCloseable, which includes all objects which implement java.io.Closeable, can be used as a resource.

The following example reads the first line from a file. It uses an instance of BufferedReader to read data from the file. BufferedReader is a resource that must be closed after the program is finished with it:

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).

Read more here : https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html

Quote from http://docs.oracle.com/javase/specs/jls/se7/html/jls-14.html#jls-14.20.3.2:

14.20.3.2 Extended try-with-resources

A try-with-resources statement with at least one catch clause and/or a finally clause is called an extended try-with-resources statement. The meaning of an extended try-with-resources statement:
try ResourceSpecification
    Block
Catches//opt
Finally//opt
is given by the following translation to a basic try-with-resources statement (§14.20.3.1) nested inside a try-catch or try-finally or try-catch-finally statement:
try {
    try ResourceSpecification
        Block
}
Catches//opt
Finally//opt
The effect of the translation is to put the ResourceSpecification "inside" the try statement. This allows a catch clause of an extended try-with-resources statement to catch an exception due to the automatic initialization or closing of any resource. So, basically, wrapper is already implemented

Running a program consist of try block but without catch or final clauses

2 Answers2