constantframemodelingvisitor.java

A static analysis tool to find bugs in Java programs

/*
 * Bytecode Analysis Framework
 * Copyright (C) 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.ba.constant;

import org.apache.bcel.generic.BIPUSH;
import org.apache.bcel.generic.ConstantPoolGen;
import org.apache.bcel.generic.ICONST;
import org.apache.bcel.generic.IINC;
import org.apache.bcel.generic.LDC;
import org.apache.bcel.generic.LDC2_W;
import org.apache.bcel.generic.SIPUSH;

import edu.umd.cs.findbugs.ba.AbstractFrameModelingVisitor;

/**
 * Visitor to model the effect of bytecode instructions
 * on ConstantFrames.
 * 
 * <p>For now, only String constants are modeled.
 * In the future we can add other kinds of constants.</p>
 * 
 * @see edu.umd.cs.findbugs.ba.constant.ConstantAnalysis
 * @author David Hovemeyer
 */
public class ConstantFrameModelingVisitor
		extends AbstractFrameModelingVisitor<Constant, ConstantFrame> {

	public ConstantFrameModelingVisitor(ConstantPoolGen cpg) {
		super(cpg);
	}

	@Override
	public Constant getDefaultValue() {
		return Constant.NOT_CONSTANT;
	}
	@Override
	public void visitIINC(IINC obj) {
		// System.out.println("before iinc: " + getFrame());
		int v = obj.getIndex();
		int amount = obj.getIncrement();
		ConstantFrame f = getFrame();
		Constant c = f.getValue(v);
		if (c.isConstantInteger())
			f.setValue(v, new Constant(c.getConstantInt() + amount));
		else f.setValue(v, Constant.NOT_CONSTANT);
		// System.out.println("after iinc: " + getFrame());
	}

	@Override
	public void visitICONST(ICONST obj) {
		Number value = obj.getValue();
		Constant c = new Constant(value);
		getFrame().pushValue(c);	
		}


	@Override
	public void visitBIPUSH(BIPUSH obj) {
		Number value = obj.getValue();
		Constant c = new Constant(value);
		getFrame().pushValue(c);
	}

	@Override
	public void visitSIPUSH(SIPUSH obj) {
		Number value = obj.getValue();
		Constant c = new Constant(value);
		getFrame().pushValue(c);
	}


	@Override
	public void visitLDC(LDC obj) {
		Object value = obj.getValue(getCPG());
		Constant c = new Constant(value);
		getFrame().pushValue(c);
	}

	@Override
	public void visitLDC2_W(LDC2_W obj) {
		Object value = obj.getValue(getCPG());
		Constant c = new Constant(value);
		getFrame().pushValue(c);
		getFrame().pushValue(c);
	}

}