Re: Problems with Try/Catch Blocks

[Andrew Huntwork]

Posting disassembly for a simple test before and after modification 
would be very helpful.  There are a couple obvious problems with the 
method you've presented:  it doesn't replace the NEW instruction that 
matches the invokespecial; and it ignores the TargetLostException that 
will certainly occur in some code.  The second problem is easily 
solvable by using InstructionHandle.setInstruction instead of 
InstructionList.insert/delete.  The first is probably an artifact of not 
seeing all your code.

Vincent Marquez wrote:
My problem is, while i'm modifying a method, if the method i'm modifying 
has a try/catch block, I get a "inconsistant stack height" error.   It 
seems this only occurs if the Try/Catch block is directly around the 
part i'm modifying.  Currently, i'm replacing a constructor from once 
class type to another.  It works perfectly except when there are 
Try/Catch blocks.  For example, if I have

1:    public static void main( String [] args ) {
2:        System.out.println( "test" );
3:        System.out.println( "anotherr test");
4:        Shape shape = new Shape();
5:        System.out.println( "final test" );
6:     }
There isn't a problem if the try/catch is around line 2 and 3.  Only if 
it encapsulates line 4, or anything after,  will there be the error.   
For legal reasons i'm unable to show all my actual code so I contrived a 
very similar example of our insturmenation method that is below.   If 
i'm doing anything wrong/stupid let me know.  If you see other problems 
with my code, feel free to let me know also, i'm always looking for ways 
to improve.  Thanks for any help/suggestions and MUCH thanks to whoever 
can solve my problem.

--vince
protected void replaceConstructor( ClassGen cg, String original_class, 
String new_class ) {

       boolean refresh = false;
       ConstantPoolGen cp_gen = cg.getConstantPool();
       ConstantPool cp        = cp_gen.getConstantPool();
       InstructionFactory factory = new InstructionFactory( cg , cp_gen );
       Method [] methods = cg.getMethods();
       for ( int x=0; x<methods.length; x++ ) {
           refresh = false;
           MethodGen method_gen = new MethodGen( methods[x], 
cg.getJavaClass().getClassName(), cp_gen );
           Iterator i = method_gen.getInstructionList().iterator();
        
           while ( i.hasNext() ) {
               InstructionHandle handle = ( InstructionHandle )i.next();

               if ( handle.getInstruction() instanceof INVOKESPECIAL && 
( ( INVOKESPECIAL )handle.getInstruction() ).getClassName( cp_gen 
).equals( original_class ) && ( ( INVOKESPECIAL )handle.getInstruction() 
).getMethodName( cp_gen ).equals( "<init>" ) ) {
                   try {
                       INVOKESPECIAL invk = ( INVOKESPECIAL 
)handle.getInstruction();
                                     
method_gen.getInstructionList().insert( invk, factory.createInvoke(
                                   new_class,
                                   "name",
                                   new ObjectType( original_class ),
                                   invk.getArgumentTypes( cp_gen ),
                                   Constants.INVOKESTATIC) );

                       // Delete the old method
                       method_gen.getInstructionList().delete( invk );
                       refresh = true;
                   } catch ( org.apache.bcel.generic.TargetLostException 
e ) {
                       Log.write( "Error", + e.toString() );
                   }
               }
           }
           if ( refresh ) {
                 method_gen.stripAttributes( false );
               method_gen.setMaxStack();
               method_gen.setMaxLocals();
              cg.replaceMethod( methods[x], method_gen.getMethod() );
           }
          }

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