src/java/org/apache/bcel/verifier/PassVerifier.java

package org.apache.bcel.verifier;

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
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 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
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 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache BCEL" must not be used to endorse or promote products
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 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

import java.util.ArrayList;

/**
 * A PassVerifier actually verifies a class file; it is instantiated
 * by a Verifier.
 * The verification should conform with a certain pass as described
 * in The Java Virtual Machine Specification, 2nd edition.
 * This book describes four passes. Pass one means loading the
 * class and verifying a few static constraints. Pass two actually
 * verifies some other constraints that could enforce loading in
 * referenced class files. Pass three is the first pass that actually
 * checks constraints in the code array of a method in the class file;
 * it has two parts with the first verifying static constraints and
 * the second part verifying structural constraints (where a data flow
 * analysis is used for). The fourth pass, finally, performs checks
 * that can only be done at run-time.
 * JustIce does not have a run-time pass, but certain constraints that
 * are usually delayed until run-time for performance reasons are also
 * checked during the second part of pass three.
 * PassVerifier instances perform caching.
 * That means, if you really want a new verification run of a certain
 * pass you must use a new instance of a given PassVerifier.
 *
 * @version $Id$
 * @author <A HREF="http://www.inf.fu-berlin.de/~ehaase"/>Enver Haase</A>
 * @see org.apache.bcel.verifier.Verifier
 * @see #verify()
 */
public abstract class PassVerifier{

	/** The (warning) messages. */
	private ArrayList messages = new ArrayList(); //Type of elements: String
	
	/** The VerificationResult cache. */
	private VerificationResult verificationResult = null;

	/**
	 * This method runs a verification pass conforming to the
	 * Java Virtual Machine Specification, 2nd edition, on a
	 * class file.
	 * PassVerifier instances perform caching;
	 * i.e. if the verify() method once determined a VerificationResult,
	 * then this result may be returned after every invocation of this
	 * method instead of running the verification pass anew; likewise with
	 * the result of getMessages().
	 *
	 * @see #getMessages()
	 * @see #addMessage(String)
	 */
	public VerificationResult verify(){
		if (verificationResult == null){
			verificationResult = do_verify();
		}
		return verificationResult;
	}

	/** Does the real verification work, uncached. */
	public abstract VerificationResult do_verify();

	/**
	 * This method adds a (warning) message to the message pool of this
	 * PassVerifier. This method is normally only internally used by
	 * BCEL's class file verifier "JustIce" and should not be used from
	 * the outside. 
	 *
	 * @see #getMessages()
	 */
	public void addMessage(String message){
		messages.add(message);
	}

	/**
	 * Returns the (warning) messages that this PassVerifier accumulated
	 * during its do_verify()ing work.
	 *
	 * @see #addMessage(String)
	 * @see #do_verify()
	 */
	public String[] getMessages(){
		verify(); // create messages if not already done (cached!)
		String[] ret = new String[messages.size()];
		for (int i=0; i<messages.size(); i++){
			ret[i] = (String) messages.get(i);
		}
		return ret;
	}
}