isnullvalueframemodelingvisitor.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;

import org.apache.bcel.generic.*;

public class IsNullValueFrameModelingVisitor extends AbstractFrameModelingVisitor<IsNullValue, IsNullValueFrame> {

	private static final boolean NO_ASSERT_HACK = Boolean.getBoolean("inva.noAssertHack");

	private AssertionMethods assertionMethods;

	public IsNullValueFrameModelingVisitor(ConstantPoolGen cpg, AssertionMethods assertionMethods) {
		super(cpg);
		this.assertionMethods = assertionMethods;
	}

	public IsNullValue getDefaultValue() {
		return IsNullValue.nonReportingNotNullValue();
	}

	// Overrides of specific instruction visitor methods.
	// ACONST_NULL obviously produces a value that is DEFINITELY NULL.
	// LDC produces values that are NOT NULL.
	// NEW produces values that are NOT NULL.

	// Note that all instructions that have an implicit null
	// check (field access, invoke, etc.) are handled in IsNullValueAnalysis,
	// because handling them relies on control flow (the existence of
	// an ETB and exception edge prior to the block containing the
	// instruction with the null check.)

	// Note that we don't override IFNULL and IFNONNULL.
	// Those are handled in the analysis itself, because we need
	// to produce different values in each of the control successors.

	private void produce(IsNullValue value) {
		IsNullValueFrame frame = getFrame();
		frame.pushValue(value);
	}

	private void produce2(IsNullValue value) {
		IsNullValueFrame frame = getFrame();
		frame.pushValue(value);
		frame.pushValue(value);
	}

	/**
	 * Handle method invocations.
	 * Generally, we want to get rid of null information following a
	 * call to a likely exception thrower or assertion.
	 */
	private void handleInvoke(InvokeInstruction obj) {
		if (IsNullValueAnalysis.UNKNOWN_VALUES_ARE_NSP) {
			// Assume that any returned value (if a reference type)
			// might be null.
			IsNullValueFrame frame = getFrame();

			int numWordsConsumed = getNumWordsConsumed(obj);
			int numWordsProduced = getNumWordsProduced(obj);

			try {
				while (numWordsConsumed-- > 0)
					frame.popValue();
			} catch (DataflowAnalysisException e) {
				throw new AnalysisException("Stack underflow", e);
			}

			if (numWordsProduced > 0) {
				Type type = obj.getType(getCPG());
				if (type instanceof ReferenceType) {
					frame.pushValue(IsNullValue.nullOnSomePathValue());
				} else {
					while (numWordsProduced-- > 0) {
						frame.pushValue(IsNullValue.nonReportingNotNullValue());
					}
				}
			}
		} else {
			// Assume returned values are non-reporting non-null.
			handleNormalInstruction(obj);
		}

		if (!NO_ASSERT_HACK) {
			if (assertionMethods.isAssertionCall(obj)) {
				IsNullValueFrame frame = getFrame();
				for (int i = 0; i < frame.getNumSlots(); ++i) {
					IsNullValue value = frame.getValue(i);
					if (value.isDefinitelyNull() || value.isNullOnSomePath()) {
						frame.setValue(i, IsNullValue.nonReportingNotNullValue());
					}
				}
			}
		}
	}

	public void visitACONST_NULL(ACONST_NULL obj) {
		produce(IsNullValue.nullValue());
	}

	public void visitNEW(NEW obj) {
		produce(IsNullValue.checkedNonNullValue());
	}

	public void visitLDC(LDC obj) {
		produce(IsNullValue.checkedNonNullValue());
	}

	public void visitLDC_W(LDC_W obj) {
		produce(IsNullValue.checkedNonNullValue());
	}

	public void visitLDC2_W(LDC2_W obj) {
		produce2(IsNullValue.checkedNonNullValue());
	}

	public void visitINVOKESTATIC(INVOKESTATIC obj) {
		handleInvoke(obj);
	}

	public void visitINVOKESPECIAL(INVOKESPECIAL obj) {
		handleInvoke(obj);
	}

	public void visitINVOKEINTERFACE(INVOKEINTERFACE obj) {
		handleInvoke(obj);
	}

	public void visitINVOKEVIRTUAL(INVOKEVIRTUAL obj) {
		handleInvoke(obj);
	}

}

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