Модификация программы и что лучше менять: исполняемый код или AST программы?

import java.awt.*;
import java.applet.*;

public class DocFooter extends Applet {
        String date;
        String email;

        public void init() {
                resize(500,100);
                date = getParameter("LAST_UPDATED");
                email = getParameter("EMAIL");
        }

        public void paint(Graphics g) {
                g.drawString(date + " by ",100, 15);
                g.drawString(email,290,15);
        }
}

Compiled from "DocFooter.java"
public class DocFooter extends java.applet.Applet {
  java.lang.String date;

  java.lang.String email;

  public DocFooter();
    Code:
       0: aload_0       
       1: invokespecial #1                  // Method java/applet/Applet."<init>":()V
       4: return        

  public void init();
    Code:
       0: aload_0       
       1: sipush        500
       4: bipush        100
       6: invokevirtual #2                  // Method resize:(II)V
       9: aload_0       
      10: aload_0       
      11: ldc           #3                  // String LAST_UPDATED
      13: invokevirtual #4                  // Method getParameter:(Ljava/lang/String;)Ljava/lang/String;
      16: putfield      #5                  // Field date:Ljava/lang/String;
      19: aload_0       
      20: aload_0       
      21: ldc           #6                  // String EMAIL
      23: invokevirtual #4                  // Method getParameter:(Ljava/lang/String;)Ljava/lang/String;
      26: putfield      #7                  // Field email:Ljava/lang/String;
      29: return        

  public void paint(java.awt.Graphics);
    Code:
       0: aload_1       
       1: new           #8                  // class java/lang/StringBuilder
       4: dup           
       5: invokespecial #9                  // Method java/lang/StringBuilder."<init>":()V
       8: aload_0       
       9: getfield      #5                  // Field date:Ljava/lang/String;
      12: invokevirtual #10                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      15: ldc           #11                 // String  by 
      17: invokevirtual #10                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      20: invokevirtual #12                 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
      23: bipush        100
      25: bipush        15
      27: invokevirtual #13                 // Method java/awt/Graphics.drawString:(Ljava/lang/String;II)V
      30: aload_1       
      31: aload_0       
      32: getfield      #7                  // Field email:Ljava/lang/String;
      35: sipush        290
      38: bipush        15
      40: invokevirtual #13                 // Method java/awt/Graphics.drawString:(Ljava/lang/String;II)V
      43: return        
}

/***
 * ASM examples: examples showing how ASM can be used
 * Copyright (c) 2000-2011 INRIA, France Telecom
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the copyright holders nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

import org.objectweb.asm.ClassReader;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.tree.AbstractInsnNode;
import org.objectweb.asm.tree.ClassNode;
import org.objectweb.asm.tree.IincInsnNode;
import org.objectweb.asm.tree.MethodNode;
import org.objectweb.asm.tree.VarInsnNode;
import org.objectweb.asm.tree.analysis.Analyzer;
import org.objectweb.asm.tree.analysis.BasicValue;
import org.objectweb.asm.tree.analysis.BasicVerifier;
import org.objectweb.asm.tree.analysis.Frame;
import org.objectweb.asm.tree.analysis.SourceInterpreter;
import org.objectweb.asm.tree.analysis.SourceValue;
import org.objectweb.asm.util.TraceMethodVisitor;
import org.objectweb.asm.util.Textifier;

/**
 * @author Eric Bruneton
 */
public class Analysis implements Opcodes {

    public static void main(final String[] args) throws Exception {
        ClassReader cr = new ClassReader("Analysis");
        ClassNode cn = new ClassNode();
        cr.accept(cn, ClassReader.SKIP_DEBUG);

        List<MethodNode> methods = cn.methods;
        for (int i = 0; i < methods.size(); ++i) {
            MethodNode method = methods.get(i);
            if (method.instructions.size() > 0) {
                if (!analyze(cn, method)) {
                    Analyzer<?> a = new Analyzer<BasicValue>(
                            new BasicVerifier());
                    try {
                        a.analyze(cn.name, method);
                    } catch (Exception ignored) {
                    }
                    final Frame<?>[] frames = a.getFrames();

                    Textifier t = new Textifier() {
                        @Override
                        public void visitMaxs(final int maxStack,
                                final int maxLocals) {
                            for (int i = 0; i < text.size(); ++i) {
                                StringBuilder s = new StringBuilder(
                                        frames[i] == null ? "null"
                                                : frames[i].toString());
                                while (s.length() < Math.max(20, maxStack
                                        + maxLocals + 1)) {
                                    s.append(' ');
                                }
                                System.err.print(Integer.toString(i + 1000)
                                        .substring(1)
                                        + " "
                                        + s
                                        + " : "
                                        + text.get(i));
                            }
                            System.err.println();
                        }
                    };
                    MethodVisitor mv = new TraceMethodVisitor(t);
                    for (int j = 0; j < method.instructions.size(); ++j) {
                        Object insn = method.instructions.get(j);
                        ((AbstractInsnNode) insn).accept(mv);
                    }
                    mv.visitMaxs(0, 0);
                }
            }
        }
    }

    /*
     * Detects unused xSTORE instructions, i.e. xSTORE instructions without at
     * least one xLOAD corresponding instruction in their successor instructions
     * (in the control flow graph).
     */
    public static boolean analyze(final ClassNode c, final MethodNode m)
            throws Exception {
        Analyzer<SourceValue> a = new Analyzer<SourceValue>(
                new SourceInterpreter());
        Frame<SourceValue>[] frames = a.analyze(c.name, m);

        // for each xLOAD instruction, we find the xSTORE instructions that can
        // produce the value loaded by this instruction, and we put them in
        // 'stores'
        Set<AbstractInsnNode> stores = new HashSet<AbstractInsnNode>();
        for (int i = 0; i < m.instructions.size(); ++i) {
            AbstractInsnNode insn = m.instructions.get(i);
            int opcode = insn.getOpcode();
            if ((opcode >= ILOAD && opcode <= ALOAD) || opcode == IINC) {
                int var = opcode == IINC ? ((IincInsnNode) insn).var
                        : ((VarInsnNode) insn).var;
                Frame<SourceValue> f = frames[i];
                if (f != null) {
                    Set<AbstractInsnNode> s = f.getLocal(var).insns;
                    Iterator<AbstractInsnNode> j = s.iterator();
                    while (j.hasNext()) {
                        insn = j.next();
                        if (insn instanceof VarInsnNode) {
                            stores.add(insn);
                        }
                    }
                }
            }
        }

        // we then find all the xSTORE instructions that are not in 'stores'
        boolean ok = true;
        for (int i = 0; i < m.instructions.size(); ++i) {
            AbstractInsnNode insn = m.instructions.get(i);
            int opcode = insn.getOpcode();
            if (opcode >= ISTORE && opcode <= ASTORE) {
                if (!stores.contains(insn)) {
                    ok = false;
                    System.err.println("method " + m.name + ", instruction "
                            + i + ": useless store instruction");
                }
            }
        }
        return ok;
    }

    /*
     * Test for the above method, with three useless xSTORE instructions.
     */
    public int test(int i, int j) {
        i = i + 1; // ok, because i can be read after this point

        if (j == 0) {
            j = 1; // useless
        } else {
            try {
                j = j - 1; // ok, because j can be accessed in the catch
                int k = 0;
                if (i > 0) {
                    k = i - 1;
                }
                return k;
            } catch (Exception e) { // useless ASTORE (e is never used)
                j = j + 1; // useless
            }
        }

        return 0;
    }
}

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