typeframe.java

A static analysis tool to find bugs in Java programs

/*
 * Bytecode Analysis Framework
 * Copyright (C) 2003-2005 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.type;

import static edu.umd.cs.findbugs.ba.Debug.VERIFY_INTEGRITY;

import java.util.BitSet;

import org.apache.bcel.generic.Type;

import edu.umd.cs.findbugs.ba.DataflowAnalysisException;
import edu.umd.cs.findbugs.ba.Frame;
import edu.umd.cs.findbugs.ba.vna.ValueNumber;

/**
 * A specialization of {@link Frame} for determining the types
 * of values in the Java stack frame (locals and operand stack).
 *
 * @author David Hovemeyer
 * @see Frame
 * @see TypeAnalysis
 */
public class TypeFrame extends Frame<Type> {
	private BitSet exactTypeSet;

	/**
	 * Constructor.
	 */
	public TypeFrame(int numLocals) {
		super(numLocals);
		this.exactTypeSet = new BitSet();
	}

	/**
	 * Set whether or not a type in a given slot is exact.
	 * 
	 * @param slot    the slot
	 * @param isExact true if the slot contains an exact type, false if just an upper bound
	 */
	public void setExact(int slot, boolean isExact) {
		exactTypeSet.set(slot, isExact);
	}

	/**
	 * Get whether or not a type in a given slot is exact.
	 * 
	 * @param slot the slot
	 * @return true if the slot contains an exact type, false if just an upper bound
	 */
	public boolean isExact(int slot) {
		return exactTypeSet.get(slot);
	}

	/**
	 * Clear the exact type set.
	 * The result is that all slots will be assumed <em>not</em> to
	 * contain an exact type.
	 */
	public void clearExactSet() {
		exactTypeSet.clear();
	}

	@Override
	public void setTop() {
		super.setTop();
		clearExactSet();
	}

	@Override
	public void copyFrom(Frame<Type> other_) {
		clearExactSet();

		TypeFrame other = (TypeFrame) other_;

		this.exactTypeSet.or(other.exactTypeSet);

		super.copyFrom(other_);
	}

	@Override
	protected String valueToString(Type value) {
		return value.toString() + ",";
	}

	/**
	 * Get the single instance of the "Top" type.
	 */
	public static Type getTopType() {
		return TopType.instance();
	}

	/**
	 * Get the single instance of the "Bottom" type.
	 */
	public static Type getBottomType() {
		return BottomType.instance();
	}

	/**
	 * Get the single instance of the "LongExtra" type.
	 */
	public static Type getLongExtraType() {
		return LongExtraType.instance();
	}

	/**
	 * Get the single instance of the "DoubleExtra" type.
	 */
	public static Type getDoubleExtraType() {
		return DoubleExtraType.instance();
	}

	/**
	 * Get the single instance of the "Null" type.
	 */
	public static Type getNullType() {
		return NullType.instance();
	}

	@Override
	public void pushValue(Type value) {

		super.pushValue(value);

		try {
			exactTypeSet.clear(getStackLocation(0));
		} catch (DataflowAnalysisException e) {
			assert false;
		}

	}

	/**
	 * Pop a value off of the Java operand stack.
	 * 
	 * @return the value that was popped
	 * @throws DataflowAnalysisException
	 *             if the Java operand stack is empty
	 */
	@Override
	public Type popValue() throws DataflowAnalysisException {

		exactTypeSet.clear(getStackLocation(0));
		return super.popValue();
	}




}

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