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ProGuard is a free shrinker, optimizer, obfuscator, and preverifier for Java bytecode
There is a newer version: 7.6.0
/*
 * ProGuard -- shrinking, optimization, obfuscation, and preverification
 *             of Java bytecode.
 *
 * Copyright (c) 2002-2020 Guardsquare NV
 *
 * 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.shrink;

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

/**
 * This ClassVisitor delegates all its method calls to another ClassVisitor,
 * depending on whether the Clazz objects are marked as used.
 *
 * @author Eric Lafortune
 */
public class UsedClassFilter
implements   ClassVisitor
{
    private final SimpleUsageMarker simpleUsageMarker;
    private final ClassVisitor      usedClassVisitor;
    private final ClassVisitor      unusedClassVisitor;


    /**
     * Creates a new UsedClassFilter.
     * @param simpleUsageMarker the marker that can tell whether classes
     *                          have been marked.
     * @param usedClassVisitor  the class visitor to which the visiting
     *                          used classes will be delegated.
     */
    public UsedClassFilter(SimpleUsageMarker simpleUsageMarker,
                           ClassVisitor      usedClassVisitor)
    {
        this(simpleUsageMarker, usedClassVisitor, null);
    }


    /**
     * Creates a new UsedClassFilter.
     * @param simpleUsageMarker  the marker that can tell whether classes
     *                           have been marked.
     * @param usedClassVisitor   the class visitor to which the visiting
     *                           used classes will be delegated.
     * @param unusedClassVisitor the class visitor to which the visiting
     *                           unused classes will be delegated.
     */
    public UsedClassFilter(SimpleUsageMarker simpleUsageMarker,
                           ClassVisitor      usedClassVisitor,
                           ClassVisitor      unusedClassVisitor)
    {
        this.simpleUsageMarker  = simpleUsageMarker;
        this.usedClassVisitor   = usedClassVisitor;
        this.unusedClassVisitor = unusedClassVisitor;
    }


    // Implementations for ClassVisitor.

    @Override
    public void visitAnyClass(Clazz clazz)
    {
        // Is the class marked?
        ClassVisitor classVisitor = simpleUsageMarker.isUsed(clazz) ?
            usedClassVisitor :
            unusedClassVisitor;

        if (classVisitor != null)
        {
            clazz.accept(classVisitor);
        }
    }
}