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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 52433] New: Why using unstable sort at MethodGen.getLocalVariables() ?
Date Thu, 05 Jan 2012 20:29:45 GMT
https://issues.apache.org/bugzilla/show_bug.cgi?id=52433

             Bug #: 52433
           Summary: Why using unstable sort at
                    MethodGen.getLocalVariables() ?
           Product: BCEL
           Version: 5.3
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Main
        AssignedTo: notifications@jakarta.apache.org
        ReportedBy: thiagobart@gmail.com
    Classification: Unclassified


I noticed that MethodGen.getLocalVariables sorts the local variables by index.
However, it uses a hand written sort algorithm that is unstable. That is, it
does not guarantee that variables with the same index are kept in the same
order. In fact, it always swaps them.

This does not cause a major problem apart from having a different order of
variables in the local variables table when a class is simply parsed and
dumped.

A simple enhancement is to use java's own merge sort implementation (available
in version 1.3, which seems to be the target platform). In getLocalVariables(),
instead of calling:

    sort(lg, 0, size - 1);

use something like (maybe remove generics):

    Arrays.sort(lg, new Comparator<LocalVariableGen>() {
        public int compare(LocalVariableGen o1, LocalVariableGen o2) {
            return o1.getIndex() - o2.getIndex();
        }
    });

The advantage, besides using a stable sort, is that this is less code to
maintain, compared to the trick sort method.

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