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Subject: Please help me regarding finally block
Date: Fri, 4 Feb 2005 21:07:22 +0100
Message-ID: <73DFF891F8024B48AD56B594C4C5038A6BDACA@dewdfe23.wdf.sap.corp>
Thread-Topic: Please help me regarding finally block
Thread-Index: AcUK0Fbl7VqZQZTKSOqcCvwgKQCV5AAAaH8QAAfcA1A=
From: "Koduru, Rajendra Kumar Reddy" <rajendra.kumar.reddy.koduru@sap.com>
To: "BCEL Users List" <bcel-user@jakarta.apache.org>

Hi All,=20
=09
	Currently i am planning to instrument each method of a class
dynamically with system.out.println() statements.
=09
	as it is not possible to get it executed, due to the return
statements which are available in middle of method,=20

	As seen from many sources, implementing it with try and finally
is a good idea.

	finally seems to be more complex to handle compared to catch
(atleast to me).

	however i got the source from internet, i could not understand
few things in the source, could some one please clarify me.

	i have directly put put my understandings and queries in the
middle of code IN CAPS, [code is given below, of course not too big]. So
please correct me and help me in this regard.

Thank you
Reddy


public void instrumentMethod (ClassGen cg, MethodGen mg)
	{
		InstructionList il =3D mg.getInstructionList();

		InstructionFactory ifact =3D new InstructionFactory(cg);

		InstructionHandle start =3D il.getStart();
		InstructionHandle end =3D il.getEnd();


		//  IN THE FOLLOWING SNIPPET OF CODE, CALL TO
SUBROUTINES ARE INSERTED AND ALL THE TARGETS OF RETURN INSTRUCTIONS ARE
CHANGED

		Collection<JSR> jsrs =3D new ArrayList<JSR>();
		for (Iterator i =3D il.iterator(); i.hasNext(); ) {
			InstructionHandle ih =3D
(InstructionHandle)i.next();

			if (ih.getInstruction() instanceof RETURN) {
				JSR jsr2 =3D new JSR(null);
				jsrs.add(jsr2);
				InstructionHandle n =3D il.insert(ih,
jsr2);
						=09
				il.redirectBranches(ih, n);
			}
		}

		// END OF ABOVE UNDERSTANDING. AM I CORRECT ??

	=09
	=09
		InstructionHandle h1 =3D il.append(new ASTORE(0)); // AT
THE CURRENT SITUATION, WHAT IS ON THE TOP OF STACK AND WHY IS IT
STORED??

		JSR jsr =3D new JSR(null);
// WHY A SUBROUTINE CALL IS DONE HERE???=20

		jsrs.add(jsr);
		il.append(jsr);

		InstructionHandle h2 =3D il.append(new ALOAD(0));	  //
REFLECTS THE ABOVE STORE OPERATION; SO WHAT IS ACTUALLY IN THIS NOW??

		il.append(new ATHROW());
// I THINK IT IS TO RETHROW THE EXCEPTION IF AN EXCEPTION ARISES

		InstructionHandle handler =3D il.append(new ASTORE(1)); //
STORES THE EXCEPTION VARIABLE

		// I WILL APPEND AN PRINTLN STATEMENT HERE=20

		il.append(new RET(1));
// RETURNING FROM SUBROUTINE, BUT DOESNT THE INDEX OF RET START AT 0

		for (JSR j : jsrs) {
			j.setTarget(handler);
		}=09

		mg.addExceptionHandler(start, end, h1, null);	//
DOESNT THE EXCEPTION HANDLER START AT HANDLE handler(which is just 3
lines above in this code)

		il.setPositions(true);
//  IS THIS NECESSARY ??
	}


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