isnullconditiondecision.java

一个查找java程序里bug的程序的源代码,该程序本身也是java写的,对提高java编程水平很有用

/*
 * Bytecode Analysis Framework
 * Copyright (C) 2003,2004 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;

/**
 * A control decision which resulted in information being gained
 * about whether a particular value is null or non-null
 * on the IFCMP_EDGE and FALL_THROUGH_EDGE branches.
 *
 * @see IsNullValue
 * @see IsNullValueFrame
 * @see IsNullValueAnalysis
 */
public class IsNullConditionDecision implements EdgeTypes {
	private final ValueNumber value;
	private final IsNullValue ifcmpDecision;
	private final IsNullValue fallThroughDecision;

	/**
	 * Constructor.
	 *
	 * @param value               the ValueNumber for which we have new information; null if no
	 *                            new information
	 * @param ifcmpDecision       the decision for the IFCMP_EDGE; null if that edge is not feasible
	 * @param fallThroughDecision the decision for the FALL_THROUGH_EDGE; null if that edge is not feasible
	 */
	public IsNullConditionDecision(ValueNumber value, IsNullValue ifcmpDecision, IsNullValue fallThroughDecision) {
		this.value = value;

		// At least one of the edges must be feasible
		assert !(ifcmpDecision == null && fallThroughDecision == null);
		this.ifcmpDecision = ifcmpDecision;
		this.fallThroughDecision = fallThroughDecision;
	}

	/**
	 * Get the value about which the branch yields information.
	 */
	public ValueNumber getValue() {
		return value;
	}

	/**
	 * Determine whether or not the comparison is redundant.
	 */
	public boolean isRedundant() {
		return ifcmpDecision == null || fallThroughDecision == null;
	}

	/**
	 * Determine whether or not the given edge is feasible.
	 * An edge may be infeasible if the comparison is redundant (i.e.,
	 * can only be determined one way)
	 *
	 * @param edgeType the type of edge; must be IFCMP_EDGE or FALL_THROUGH_EDGE
	 * @return true if the edge is feasible, false if infeasible
	 */
	public boolean isEdgeFeasible(int edgeType) {
		IsNullValue decision = getDecision(edgeType);
		return decision != null;
	}

	/**
	 * Get the decision reached about the value on outgoing edge of given type.
	 *
	 * @param edgeType the type of edge; must be IFCMP_EDGE or FALL_THROUGH_EDGE
	 * @return the IsNullValue representing the decision, or null
	 *         if the edge is infeasible
	 */
	public IsNullValue getDecision(int edgeType) {
		assert edgeType == IFCMP_EDGE || edgeType == FALL_THROUGH_EDGE;
		if (edgeType == IFCMP_EDGE)
			return ifcmpDecision;
		else
			return fallThroughDecision;
	}

	public String toString() {
		StringBuffer buf = new StringBuffer();
		buf.append(value != null ? value.toString() : "NoValue,");
		buf.append("ifcmp=");
		buf.append(ifcmpDecision != null ? ifcmpDecision.toString() : "INFEASIBLE");
		buf.append(",fallthru=");
		buf.append(fallThroughDecision != null ? fallThroughDecision.toString() : "INFEASIBLE");
		return buf.toString();
	}
}

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