JLS3 14.21 Spec for reachability doesn't consider unchecked exceptions

Name: ngC57085 Date: 04/22/97



Java compiler (JDK1.1.2) does not report about unreachable catch block
while compile try statement.

JLS (14.19) says:

"
A catch block C is reachable iff both of the following are true:

   Some expression or throw statement in the try block is reachable and can
   throw an exception whose type is assignable to the parameter of the catch
   clause C. (An expression is considered reachable iff the innermost statement
   containing it is reachable.)

   There is no earlier catch block A in the try statement such that the type
   of C's parameter is the same as or a subclass of the type of A's parameter.
"

A catch block is not reachable if there is no some expression or throw
statement in the try block that can throw an exception.

Test stmt15204, where try block is empty, is compiled successfully by JDK1.1.2 instead of error message.

> javac112 stmt15104.java
>

------------------------stmt15104--------------
import java.io.PrintStream;

public class stmt15104 {
  public static void main(String argv[]) {
     System.exit(run(argv, System.out) + 95/*STATUS_TEMP*/);
  }
  public static int run(String argv[],PrintStream out) {
     int a1 = 1;
     int a2 = 1;
     int a3 = 1;
     int a4 = 1;
     a1 = 2;
     try {
     }
     catch (ArithmeticException e) {
        a2 = 2;
     }
     catch (Exception e) {
        a3 = 2;
     }
     a4 = 2;
     return 2/*STATUS_FAILED*/;
  }
}
--------------------------------------

======================================================================

From duplicate bug 4313756:

Compilation of the following examples successfuly complete, but error message expected.

class X {
   void check_unreachable () {
      try {
      } catch(Exception e) {
         int i = 10; // error: statement not reached
      }
   }
}

class X {
   static void check_unreachable () {
      try {
         return;
      } catch(Error e) {} // error: statement not reached
   }
}

This behavior violates JLS 14.19

konstantin.boudnik@eng 2000-02-17

======================================================================

From duplicate bug 4087302:


allan.jacobs@Eng 1997-10-20

The following example is motivated by Modena test n1419206.

// import java.io.IOException;
class X {
  static void check_unexception () {
    try{ }
    catch( Exception e) { System.out.println(e); }
  }
  static void check_unreachable () {
    try{ }
    catch( Throwable e) { System.out.println(e); }
  }
  public static void main( String[] argv ) {
    X.check_unthrowable();
    X.check_unexception();
  }
}

Section 14.19:
"A catch block C is reachable iff both of the following are true:
* Some expression or throw statement in the try block is reachable and
  can throw an exception whose type is assignable to the parameter of the
  catch clause C. (An expression is considered reachable iff the
  innermost statement containing it is reachable.)
* There is no earlier catch block A in the try statement such that the
  type of C's parameter is the same as or a subclass of the type of A's
  parameter.

Are the println's reachable? Javac says so but the spec (at least by
the most direct reading) says not. Which catch block arguments do make
their catch block's unreachable when their corresponding try blocks are
empty?

=========================================================================
Here's another test case from ###@###.###. I would expect this one to fail at compile-time also.
brian.klock@eng 1998-07-23

//-----------------------------Test1.java---------------------------
public class Test1 {
    public static void main(String args[]) throws Exception
    {
        try { throw new Exception(); }
        catch(SubException e) { System.out.println("Caught 1"); }

        try { m(); }
        catch(SubException e) { System.out.println("Caught 2"); }
    }

    static void m() throws Exception { throw new SubException(); }
}

class SubException extends Exception { }
###@###.### 10/22/04 14:12 GMT