methodlinker.java

ProGuard 是一个免费的 Java类文件的压缩

/*
 * ProGuard -- shrinking, optimization, obfuscation, and preverification
 *             of Java bytecode.
 *
 * Copyright (c) 2002-2007 Eric Lafortune ([e-mail])
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package proguard.classfile.util;

import proguard.classfile.*;
import proguard.classfile.visitor.*;

import java.util.*;

/**
 * This ClassVisitor links all corresponding non-private methods in the class
 * hierarchies of all visited classes. Visited classes are typically all class
 * files that are not being subclassed. Chains of links that have been created
 * in previous invocations are merged with new chains of links, in order to
 * create a consistent set of chains.
 * <p>
 * As a MemberVisitor, it links all corresponding class members that it visits,
 * including fields and private class members.
 * <p>
 * Class initialization methods and constructors are always ignored.
 *
 * @author Eric Lafortune
 */
public class MethodLinker
extends      SimplifiedVisitor
implements   ClassVisitor,
             MemberVisitor
{
    // An object that is reset and reused every time.
    // The map: [class member name+' '+descriptor - class member info]
    private final Map memberMap = new HashMap();


    // Implementations for ClassVisitor.

    public void visitAnyClass(Clazz clazz)
    {
        // Collect all non-private members in this class hierarchy.
        clazz.hierarchyAccept(true, true, true, false,
            new AllMethodVisitor(
            new MemberAccessFilter(0, ClassConstants.INTERNAL_ACC_PRIVATE,
            this)));

        // Clean up for the next class hierarchy.
        memberMap.clear();
    }


    // Implementations for MemberVisitor.

    public void visitAnyMember(Clazz clazz, Member member)
    {
        // Get the class member's name and descriptor.
        String name       = member.getName(clazz);
        String descriptor = member.getDescriptor(clazz);

        // Special cases: <clinit> and <init> are always kept unchanged.
        // We can ignore them here.
        if (name.equals(ClassConstants.INTERNAL_METHOD_NAME_CLINIT) ||
            name.equals(ClassConstants.INTERNAL_METHOD_NAME_INIT))
        {
            return;
        }

        // Get the last method in the chain.
        Member thisLastMember = lastMember(member);

        // See if we've already come across a method with the same name and
        // descriptor.
        String key = name + ' ' + descriptor;
        Member otherMember = (Member)memberMap.get(key);

        if (otherMember == null)
        {
            // Store the new class method in the map.
            memberMap.put(key, thisLastMember);
        }
        else
        {
            // Get the last method in the other chain.
            Member otherLastMember = lastMember(otherMember);

            // Check if both link chains aren't already ending in the same element.
            if (!thisLastMember.equals(otherLastMember))
            {
                // Merge the two chains, with the library members last.
                if (otherLastMember instanceof LibraryMember)
                {
                    thisLastMember.setVisitorInfo(otherLastMember);
                }
                else
                {
                    otherLastMember.setVisitorInfo(thisLastMember);
                }
            }
        }
    }


    // Small utility methods.

    /**
     * Finds the last class member in the linked list of related class members.
     * @param member the given class member.
     * @return the last class member in the linked list.
     */
    public static Member lastMember(Member member)
    {
        Member lastMember = member;
        while (lastMember.getVisitorInfo() != null &&
               lastMember.getVisitorInfo() instanceof Member)
        {
            lastMember = (Member)lastMember.getVisitorInfo();
        }

        return lastMember;
    }


    /**
     * Finds the last visitor accepter in the linked list of visitors.
     * @param visitorAccepter the given method.
     * @return the last method in the linked list.
     */
    public static VisitorAccepter lastVisitorAccepter(VisitorAccepter visitorAccepter)
    {
        VisitorAccepter lastVisitorAccepter = visitorAccepter;
        while (lastVisitorAccepter.getVisitorInfo() != null &&
               lastVisitorAccepter.getVisitorInfo() instanceof VisitorAccepter)
        {
            lastVisitorAccepter = (VisitorAccepter)lastVisitorAccepter.getVisitorInfo();
        }

        return lastVisitorAccepter;
    }
}