Re: Struggling with understanding indexes...

[Mark R. Diggory]

Great, problem solved... :-)

I have to say BsfLifier is a great little program. I REALLY like that I can generate simple examples dynamically like this. It really advanced my "mental model" of the package faster than if I had too read alot of online doc to get an understanding. Kudos!

-Mark

Juozas Baliuka wrote:

yes, it is true, you need 2 index spaces for double and long, but 1 for
float, int, ...,object and "special" types.

Ah ha! Does this mean I need to allow 2 index spaces for double and long
as well? This seems to be the case, when I tried it in my code and it
the problem went away.

Thanks,
-Mark

Juozas Baliuka wrote:

double and long use two registers.

do you have problems with long and double type ?

Thanks,

Would the following stack trace be related to these indexes? I'm
assuming that Registers are analogous to entries in the index? Whould
this be correct?

java.lang.VerifyError: (class: foo/bar/NewTestBean, method: testMethod
signature: (DI)D) Register 2 contains wrong type
at java.lang.Class.getDeclaredConstructors0(Native Method)
at

java.lang.Class.privateGetDeclaredConstructors(Class.java:1576)

at java.lang.Class.getConstructor0(Class.java:1748)
at java.lang.Class.newInstance0(Class.java:266)
at java.lang.Class.newInstance(Class.java:249)
at

org.apache.commons.jelly.tags.bcel.BsfClassExtender.main(BsfClassExtender.ja

va:194)

Exception in thread "main"


-Mark

Bob Lee wrote:

You are correct. I'm pretty sure the indexes work like this (I
personally use Javassist):

Static method:
0..n: arguments.
n+1..m: local variables.

Instance method:
0: this
1..n: arguments.
n+1..m: local variables.

"load" pushes the variable at that index on to the stack.
"store" pops the top value off of the stack and stores it in the
specified index.

Thanks,
Bob

On Thursday, January 30, 2003, at 07:54 PM, Mark R. Diggory wrote:

Hi,

I currently have this code fragment

*
Integer xyz = new Integer(foo);
manager.declareBean("foo", xyz, xyz.getClass());
*

Which I use BCELLifier on to get the following section of BCEL code:

InstructionHandle ih_14 =
il.append(_factory.createNew("java.lang.Integer"));
il.append(InstructionConstants.DUP);
il.append(_factory.createLoad(Type.INT, 1));
il.append(_factory.createInvoke("java.lang.Integer",
"<init>",Type.VOID,new Type[] { Type.INT },

Constants.INVOKESPECIAL));

il.append(_factory.createStore(Type.OBJECT, 3));
InstructionHandle ih_23 = il.append(_factory.createLoad(Type.OBJECT,
0));

il.append(_factory.createFieldAccess("org.apache.commons.jelly.tags.bce

l.Test","manager",new ObjectType("com.ibm.bsf.BSFManager"),
Constants.GETFIELD));
il.append(new PUSH(_cp, "foo"));
il.append(_factory.createLoad(Type.OBJECT, 3));
il.append(_factory.createLoad(Type.OBJECT, 3));
il.append(_factory.createInvoke("java.lang.Object", "getClass", new
ObjectType("java.lang.Class"), Type.NO_ARGS, >

Constants.INVOKEVIRTUAL));

il.append(_factory.createInvoke("com.ibm.bsf.BSFManager",
"declareBean",Type.VOID, new Type[] { Type.STRING, Type.OBJECT, new
ObjectType("java.lang.Class") }, Constants.INVOKEVIRTUAL));


Specifically, I'm struggling with some issues where I don't quite
understand what the indexes are for in situations like

_factory.createStore(Type.OBJECT, 3)

and

_factory.createLoad(Type.OBJECT, 3)

am I right in assuming that there are a set number of "indexes"
representing positions in the InstructionList and that these above
references represent the setting and getting of Object references in
that list?

I'm struggling because I'm trying to make the code more "iterative"
where I might iterate over a "set" of handlers/append statements to
append repeatedly to the instruction list (as an Example):

for(int i = 0; i < argNames.length ; ){

InstructionHandle ih_14 =

il.append(_factory.createNew(argClasses[i]));

...
il.append(_factory.createStore(Type.OBJECT, i));
...
il.append(new PUSH(_cp, argName[i]));
il.append(_factory.createLoad(Type.OBJECT, i));
il.append(_factory.createLoad(Type.OBJECT, i));
...

}

My problem is that I get actuall references that end up pointing to
only the first argument. I'm hoping I understand what the indexes are
for, but I'm hoping that you guy's can clarify this for me.

Thanks,
-Mark Diggory



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