SuperfluousInstanceOf.java

/*
 * FindBugs - Find bugs in Java programs
 * Copyright (C) 2004-2005 Dave Brosius <dbrosius@users.sourceforge.net>
 * Copyright (C) 2004-2005 University of Maryland
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package edu.umd.cs.findbugs.detect;

import org.apache.bcel.classfile.Code;
import org.apache.bcel.classfile.LocalVariable;
import org.apache.bcel.classfile.LocalVariableTable;
import org.apache.bcel.classfile.Method;

import edu.umd.cs.findbugs.BugInstance;
import edu.umd.cs.findbugs.BugReporter;
import edu.umd.cs.findbugs.BytecodeScanningDetector;
import edu.umd.cs.findbugs.StatelessDetector;
import edu.umd.cs.findbugs.visitclass.LVTHelper;

/**
 * Find occurrences of a instanceof b where it can be determined statically
 * whether this is true or false. This may signal a misunderstanding of the
 * inheritance hierarchy in use, and potential bugs.
 * 
 * @author Dave Brosius
 */
public class SuperfluousInstanceOf extends BytecodeScanningDetector implements StatelessDetector {

    private static final int SEEN_NOTHING = 0;

    private static final int SEEN_ALOAD = 1;

    private BugReporter bugReporter;

    private LocalVariableTable varTable;

    private int state;

    private int register;

    public SuperfluousInstanceOf(BugReporter bugReporter) {
        this.bugReporter = bugReporter;
    }

    @Override
    public void visit(Method obj) {
        state = SEEN_NOTHING;
        varTable = obj.getLocalVariableTable();
        if (varTable != null)
            super.visit(obj);
    }

    @Override
    public void visit(Code obj) {
        if (varTable != null)
            super.visit(obj);
    }

    @Override
    public void sawOpcode(int seen) {
        switch (state) {
        case SEEN_NOTHING:
            if (seen == ALOAD)
                register = getRegisterOperand();
            else if ((seen >= ALOAD_0) && (seen <= ALOAD_3))
                register = seen - ALOAD_0;
            else
                return;
            state = SEEN_ALOAD;
            break;

        case SEEN_ALOAD:
            try {
                if (seen == INSTANCEOF) {
                    LocalVariable lv = LVTHelper.getLocalVariableAtPC(varTable, register, getPC());
                    if (lv != null) {
                        String objSignature = lv.getSignature();
                        if (objSignature.charAt(0) == 'L') {
                            objSignature = objSignature.substring(1, objSignature.length() - 1).replace('/', '.');
                            String clsSignature = getDottedClassConstantOperand();

                            if (clsSignature.charAt(0) != '[') {
                                if (org.apache.bcel.Repository.instanceOf(objSignature, clsSignature)) {
                                    bugReporter.reportBug(new BugInstance(this, "SIO_SUPERFLUOUS_INSTANCEOF", LOW_PRIORITY)
                                            .addClassAndMethod(this).addSourceLine(this));
                                }
                            }
                        }
                    }
                }
            } catch (ClassNotFoundException cnfe) {
                bugReporter.reportMissingClass(cnfe);
            }

            state = SEEN_NOTHING;
            break;
        }

    }
}

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