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List:       bcel-user
Subject:    RE: Extract Constructor Code to new method
From:       Felix Dorner <FDorner () zed ! com>
Date:       2009-07-02 14:54:52
Message-ID: FC95BD382E2CF447BAA1B2AF1F9FFFE602628AD26F () MX034ZED0001 ! TIFDOM ! COM
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Hi Abdullah,

> InstructionList il = new InstructionList(); Method
> theOldConstructor = cg.containsMethod("<>", "()V"); MethodGen
> theNewConstructor = new MethodGen(Constants.ACC_PUBLIC,
> Type.VOID, Type.NO_ARGS, NO_STRINGS, "<init>",
> cg.getClassName(), il, cpg);
> il.append(ifact.createInvoke(cg.getSuperclassName(),
> "<init>", Type.VOID, Type.NO_ARGS, Constants.INVOKESPECIAL));
> il.append(InstructionConstants.RETURN);
> cg.replaceMethod(theOldConstructor,
> theNewConstructor.getMethod()); il.dispose(); cg.setConstantPool(cpg);


Wouldn't this just 'delete' the old constructor, and create a new 'default' one?
What misses is to move the code that's inside the old constructor into an ordinairy \
method. What I came up with so far was to:

/* look up the default constructor */
Method constructor_method = getConstructors().get(0);
ConstantPoolGen cpgen = new ConstantPoolGen(jc.getConstantPool());

MethodGen constructor = new MethodGen(constructor_method, jc.getClassName(), new \
ConstantPoolGen(jc.getConstantPool())); InstructionList constructor_code = \
constructor.getInstructionList();

/* a new method. Later I'd need to find a unique name.. I also copy the constructor's \
instruction list*/ MethodGen newmethod = new MethodGen(Constants.ACC_PUBLIC, \
Type.VOID, new Type[] {}, new String[] {}, "xaxaxa", jc.getClassName(),  \
constructor_code.copy() , cpgen);

InstructionHandle[] newmethod_instructions = \
newmethod.getInstructionList().getInstructionHandles();

/* remove the first two instructions (the one that loads the object variable this,
And the invocation of the super-constructor... */
try {
        newmethod.getInstructionList().delete(newmethod_instructions[0], \
newmethod_instructions[1]); } catch (TargetLostException e) {
        /* not only the target is lost here.. But me too.. :-)
        e.printStackTrace();
}

... Now I'd probably need to handle
 * local variables
 * exception handlers
..

What I don't really pick up is the instruction target exceptions (which in fact get \
thrown by several LineNumberGen's in my tests..)

Felix

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