One-Trick Optimiser

This essay is about a suggested student project in Java programming. This essay gives a rough overview of how it might work. It does not describe an actual complete program. I have no source, object, specifications, file layouts or anything else useful to implementing this project. Everything I have to say to help you with this project is written below. I am not prepared to help you implement it; I have too many other projects of my own.

I do contract work for a living, which could include writing a program such as this. However, I don’t do people’s homework for them. That just robs them of an education.

You have my full permission to implement this project any way you please.

Consider the following piece of Java code:

String MyString = "" ;
myString += "this" ;
myString += "that" ;
myString += "else" ;

It would more efficiently have been coded:

StringBuffer s = new StringBuffer();
s.append( "this" );
s.append( "that" );
s.append( "else" );
String myString = s.toString();
s = null ;

Your job is to take a class file and look for the first pattern in the JVM byte codes and replace it with the second. Once you have done that you might think of other one-trick optimisers that work on class files. You can cascade them together including ones from other sources. Other possibilities for optimisers include:

Replacing long cascaded ifs with Hashtables or binary search.
Nullifying references at points you can be sure they will never be needed again.
Checking the scope of local variables, and seeing if you can arrange that several share the same stack slot.
Replacing calls to standard library functions with calls to optimised ones. This is relatively easy compared with the other optimisers.
Modifying code to work with some older or newer JVM, and warning when changes can’t be done automatically.
Removing unused code.

JASM for hints on analysing class files
optimiser

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