/*
 * FindBugs - Find bugs in Java programs
 * Copyright (C) 2003, 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.detect;
import edu.umd.cs.findbugs.*;
import java.util.*;
import java.io.PrintStream;
import org.apache.bcel.classfile.*;
import java.util.zip.*;
import java.io.*;

import edu.umd.cs.pugh.visitclass.DismantleBytecode;
import edu.umd.cs.pugh.visitclass.Constants2;

public class PreferZeroLengthArrays extends BytecodeScanningDetector implements   Constants2 {
    boolean nullOnTOS = false;
    private BugReporter bugReporter;

  public PreferZeroLengthArrays(BugReporter bugReporter) {
	this.bugReporter = bugReporter;
  }

   public void visit(Code obj) {
	String returnType = methodSig.substring(methodSig.indexOf(")")+1);
	if (returnType.startsWith("[")) {
		nullOnTOS = false;
		super.visit(obj);
		}
	}


    public void sawOpcode(int seen) {

	switch (seen) {
	case ACONST_NULL:
		nullOnTOS = true;
		return;
	case ARETURN:
		if (nullOnTOS) 
                  bugReporter.reportBug(new BugInstance("PZLA_PREFER_ZERO_LENGTH_ARRAYS", LOW_PRIORITY)
                        .addClassAndMethod(this)
                        .addSourceLine(this, PC));
		break;
	}
	nullOnTOS = false;
	}
}

Check for methods with array return type that return null