/*
 * 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 java.util.Collections;
import java.util.HashSet;
import java.util.Set;

import javax.annotation.CheckForNull;
import javax.annotation.Nonnull;

import org.apache.bcel.Constants;
import org.apache.bcel.Repository;
import org.apache.bcel.classfile.Field;
import org.apache.bcel.classfile.JavaClass;
import org.apache.bcel.classfile.Method;
import org.apache.bcel.generic.ArrayType;
import org.apache.bcel.generic.ConstantPoolGen;
import org.apache.bcel.generic.FieldInstruction;
import org.apache.bcel.generic.INVOKESTATIC;
import org.apache.bcel.generic.Instruction;
import org.apache.bcel.generic.InvokeInstruction;
import org.apache.bcel.generic.ObjectType;
import org.apache.bcel.generic.ReferenceType;
import org.apache.bcel.generic.Type;

import edu.umd.cs.findbugs.SystemProperties;
import edu.umd.cs.findbugs.ba.ch.Subtypes2;
import edu.umd.cs.findbugs.ba.type.NullType;
import edu.umd.cs.findbugs.ba.type.TypeFrame;
import edu.umd.cs.findbugs.classfile.CheckedAnalysisException;
import edu.umd.cs.findbugs.classfile.ClassDescriptor;
import edu.umd.cs.findbugs.classfile.DescriptorFactory;
import edu.umd.cs.findbugs.classfile.Global;
import edu.umd.cs.findbugs.internalAnnotations.DottedClassName;

/**
 * Facade for class hierarchy queries. These typically access the class
 * hierarchy using the {@link org.apache.bcel.Repository} class. Callers should
 * generally expect to handle ClassNotFoundException for when referenced classes
 * can't be found.
 *
 * @author David Hovemeyer
 */
public class Hierarchy {
    protected static final boolean DEBUG_METHOD_LOOKUP = SystemProperties.getBoolean("hier.lookup.debug");

    public static ClassDescriptor RUNTIME_EXCEPTION = DescriptorFactory.createClassDescriptor(RuntimeException.class);
    public static ClassDescriptor EXCEPTION = DescriptorFactory.createClassDescriptor(Exception.class);
    public static ClassDescriptor ERROR = DescriptorFactory.createClassDescriptor(Error.class);

    /**
     * Type of java.lang.Exception.
     */
    public static final ObjectType EXCEPTION_TYPE = ObjectTypeFactory.getInstance("java.lang.Exception");

    /**
     * Type of java.lang.Error.
     */
    public static final ObjectType ERROR_TYPE = ObjectTypeFactory.getInstance("java.lang.Error");

    /**
     * Type of java.lang.RuntimeException.
     */
    public static final ObjectType RUNTIME_EXCEPTION_TYPE = ObjectTypeFactory.getInstance("java.lang.RuntimeException");

    /**
     * Determine whether one class (or reference type) is a subtype of another.
     *
     * @param clsName
     *            the name of the class or reference type
     * @param possibleSupertypeClassName
     *            the name of the possible superclass
     * @return true if clsName is a subtype of possibleSupertypeClassName, false
     *         if not
     */
    public static boolean isSubtype(@DottedClassName String clsName, @DottedClassName String possibleSupertypeClassName) throws ClassNotFoundException {
        Subtypes2 subtypes2 = Global.getAnalysisCache().getDatabase(Subtypes2.class);
        return subtypes2.isSubtype(DescriptorFactory.createClassDescriptorFromDottedClassName(clsName), DescriptorFactory.createClassDescriptorFromDottedClassName(possibleSupertypeClassName));
    }

    /**
     * Determine if one reference type is a subtype of another.
     *
     * @param t
     *            a reference type
     * @param possibleSupertype
     *            the possible supertype
     * @return true if t is a subtype of possibleSupertype, false if not
     */
    public static boolean isSubtype(ReferenceType t, ReferenceType possibleSupertype) throws ClassNotFoundException {
        return Global.getAnalysisCache().getDatabase(Subtypes2.class).isSubtype(t, possibleSupertype);
    }


    /**
     * Determine if the given ObjectType reference represents a
     * <em>universal</em> exception handler. That is, one that will catch any
     * kind of exception.
     *
     * @param catchType
     *            the ObjectType of the exception handler
     * @return true if catchType is null, or if catchType is java.lang.Throwable
     */
    public static boolean isUniversalExceptionHandler(ObjectType catchType) {
        return catchType == null || catchType.equals(Type.THROWABLE);
    }

    /**
     * Determine if the given ObjectType refers to an unchecked exception
     * (RuntimeException or Error).
     */
    public static boolean isUncheckedException(ObjectType type) throws ClassNotFoundException {
        if (type.equals(Type.THROWABLE) || type.equals(RUNTIME_EXCEPTION_TYPE) || type.equals(ERROR_TYPE)) {
            return true;
        }
        ClassDescriptor c = DescriptorFactory.getClassDescriptor(type);
        Subtypes2 subtypes2 = Global.getAnalysisCache().getDatabase(Subtypes2.class);
        return subtypes2.isSubtype(c, RUNTIME_EXCEPTION, ERROR);

    }

    /**
     * Determine if method whose name and signature is specified is a monitor
     * wait operation.
     *
     * @param methodName
     *            name of the method
     * @param methodSig
     *            signature of the method
     * @return true if the method is a monitor wait, false if not
     */
    public static boolean isMonitorWait(String methodName, String methodSig) {
        return "wait".equals(methodName) && ("()V".equals(methodSig) || "(J)V".equals(methodSig) || "(JI)V".equals(methodSig));
    }

    /**
     * Determine if given Instruction is a monitor wait.
     *
     * @param ins
     *            the Instruction
     * @param cpg
     *            the ConstantPoolGen for the Instruction
     *
     * @return true if the instruction is a monitor wait, false if not
     */
    public static boolean isMonitorWait(Instruction ins, ConstantPoolGen cpg) {
        if (!(ins instanceof InvokeInstruction)) {
            return false;
        }
        if (ins.getOpcode() == Constants.INVOKESTATIC) {
            return false;
        }

        InvokeInstruction inv = (InvokeInstruction) ins;
        String methodName = inv.getMethodName(cpg);
        String methodSig = inv.getSignature(cpg);

        return isMonitorWait(methodName, methodSig);
    }

    /**
     * Determine if method whose name and signature is specified is a monitor
     * notify operation.
     *
     * @param methodName
     *            name of the method
     * @param methodSig
     *            signature of the method
     * @return true if the method is a monitor notify, false if not
     */
    public static boolean isMonitorNotify(String methodName, String methodSig) {
        return ("notify".equals(methodName) || "notifyAll".equals(methodName)) && "()V".equals(methodSig);
    }

    /**
     * Determine if given Instruction is a monitor wait.
     *
     * @param ins
     *            the Instruction
     * @param cpg
     *            the ConstantPoolGen for the Instruction
     *
     * @return true if the instruction is a monitor wait, false if not
     */
    public static boolean isMonitorNotify(Instruction ins, ConstantPoolGen cpg) {
        if (!(ins instanceof InvokeInstruction)) {
            return false;
        }
        if (ins.getOpcode() == Constants.INVOKESTATIC) {
            return false;
        }

        InvokeInstruction inv = (InvokeInstruction) ins;
        String methodName = inv.getMethodName(cpg);
        String methodSig = inv.getSignature(cpg);

        return isMonitorNotify(methodName, methodSig);
    }

    /**
     * Look up the method referenced by given InvokeInstruction. This method
     * does <em>not</em> look for implementations in super or subclasses
     * according to the virtual dispatch rules.
     *
     * @param inv
     *            the InvokeInstruction
     * @param cpg
     *            the ConstantPoolGen used by the class the InvokeInstruction
     *            belongs to
     * @return the JavaClassAndMethod, or null if no such method is defined in
     *         the class
     */
    public static JavaClassAndMethod findExactMethod(InvokeInstruction inv, ConstantPoolGen cpg) throws ClassNotFoundException {
        return findExactMethod(inv, cpg, ANY_METHOD);
    }

    /**
     * Look up the method referenced by given InvokeInstruction. This method
     * does <em>not</em> look for implementations in super or subclasses
     * according to the virtual dispatch rules.
     *
     * @param inv
     *            the InvokeInstruction
     * @param cpg
     *            the ConstantPoolGen used by the class the InvokeInstruction
     *            belongs to
     * @param chooser
     *            JavaClassAndMethodChooser to use to pick the method from among
     *            the candidates
     * @return the JavaClassAndMethod, or null if no such method is defined in
     *         the class
     */
    public static JavaClassAndMethod findExactMethod(InvokeInstruction inv, ConstantPoolGen cpg, JavaClassAndMethodChooser chooser)
            throws ClassNotFoundException {
        String className = inv.getClassName(cpg);
        String methodName = inv.getName(cpg);
        String methodSig = inv.getSignature(cpg);

        JavaClass jclass = Repository.lookupClass(className);
        return findMethod(jclass, methodName, methodSig, chooser);
    }

    /**
     * Visit all superclass methods which the given method overrides.
     *
     * @param method
     *            the method
     * @param chooser
     *            chooser which visits each superclass method
     * @return the chosen method, or null if no method is chosen
     * @throws ClassNotFoundException
     */
    public static JavaClassAndMethod visitSuperClassMethods(JavaClassAndMethod method, JavaClassAndMethodChooser chooser)
            throws ClassNotFoundException {
        return findMethod(method.getJavaClass().getSuperClasses(), method.getMethod().getName(), method.getMethod()
                .getSignature(), chooser);
    }

    /**
     * Visit all superinterface methods which the given method implements.
     *
     * @param method
     *            the method
     * @param chooser
     *            chooser which visits each superinterface method
     * @return the chosen method, or null if no method is chosen
     * @throws ClassNotFoundException
     */
    public static JavaClassAndMethod visitSuperInterfaceMethods(JavaClassAndMethod method, JavaClassAndMethodChooser chooser)
            throws ClassNotFoundException {
        return findMethod(method.getJavaClass().getAllInterfaces(), method.getMethod().getName(), method.getMethod()
                .getSignature(), chooser);
    }

    /**
     * Find the least upper bound method in the class hierarchy which could be
     * called by the given InvokeInstruction. One reason this method is useful
     * is that it indicates which declared exceptions are thrown by the called
     * methods.
     *
     * <p/>
     * <ul>
     * <li>For invokespecial, this is simply an exact lookup.
     * <li>For invokestatic and invokevirtual, the named class is searched,
     * followed by superclasses up to the root of the object hierarchy
     * (java.lang.Object). Yes, invokestatic really is declared to check
     * superclasses. See VMSpec, 2nd ed, sec. 5.4.3.3.
     * <li>For invokeinterface, the named class is searched, followed by all
     * interfaces transitively declared by the class. (Question: is the order
     * important here? Maybe the VM spec requires that the actual interface
     * desired is given, so the extended lookup will not be required. Should
     * check.)
     * </ul>
     *
     * @param inv
     *            the InvokeInstruction
     * @param cpg
     *            the ConstantPoolGen used by the class the InvokeInstruction
     *            belongs to
     * @return the JavaClassAndMethod, or null if no matching method can be
     *         found
     */
    public static @CheckForNull
    JavaClassAndMethod findInvocationLeastUpperBound(InvokeInstruction inv, ConstantPoolGen cpg) throws ClassNotFoundException {
        return findInvocationLeastUpperBound(inv, cpg, ANY_METHOD);
    }

    public static @CheckForNull
    JavaClassAndMethod findInvocationLeastUpperBound(InvokeInstruction inv, ConstantPoolGen cpg,
            JavaClassAndMethodChooser methodChooser) throws ClassNotFoundException {

        if (DEBUG_METHOD_LOOKUP) {
            System.out.println("Find prototype method for " + SignatureConverter.convertMethodSignature(inv, cpg));
        }

        short opcode = inv.getOpcode();

        if (opcode == Constants.INVOKESTATIC) {
            if (methodChooser == INSTANCE_METHOD) {
                return null;
            }
        } else {
            if (methodChooser == STATIC_METHOD) {
                return null;
            }
        }

        // Find the method
        if (opcode == Constants.INVOKESPECIAL) {
            // Non-virtual dispatch
            return findExactMethod(inv, cpg, methodChooser);
        } else {
            String className = inv.getClassName(cpg);
            String methodName = inv.getName(cpg);
            String methodSig = inv.getSignature(cpg);
            if (DEBUG_METHOD_LOOKUP) {
                System.out.println("[Class name is " + className + "]");
                System.out.println("[Method name is " + methodName + "]");
                System.out.println("[Method signature is " + methodSig + "]");
            }

            if (className.startsWith("[")) {
                // Java 1.5 allows array classes to appear as the class name
                className = "java.lang.Object";
            }

            JavaClass jClass = Repository.lookupClass(className);
            return findInvocationLeastUpperBound(jClass, methodName, methodSig, methodChooser,
                    opcode == Constants.INVOKEINTERFACE);

        }
    }

    public static @CheckForNull
    JavaClassAndMethod findInvocationLeastUpperBound(JavaClass jClass, String methodName, String methodSig,
            JavaClassAndMethodChooser methodChooser, boolean invokeInterface) throws ClassNotFoundException {
        JavaClassAndMethod result = findMethod(jClass, methodName, methodSig, methodChooser);
        if (result != null) {
            return result;
        }
        if (invokeInterface) {
            for (JavaClass i : jClass.getInterfaces()) {
                result = findInvocationLeastUpperBound(i, methodName, methodSig, methodChooser, invokeInterface);
                if (result != null) {
                    return null;
                }
            }
        } else {
            JavaClass sClass = jClass.getSuperClass();
            if (sClass != null) {
                return findInvocationLeastUpperBound(sClass, methodName, methodSig, methodChooser, invokeInterface);
            }
        }
        return null;

    }

    /**
     * Find the declared exceptions for the method called by given instruction.
     *
     * @param inv
     *            the InvokeInstruction
     * @param cpg
     *            the ConstantPoolGen used by the class the InvokeInstruction
     *            belongs to
     * @return array of ObjectTypes of thrown exceptions, or null if we can't
     *         find the list of declared exceptions
     * @deprecated Use
     *             {@link Hierarchy2#findDeclaredExceptions(InvokeInstruction,ConstantPoolGen)}
     *             instead
     */
    @Deprecated
    public static ObjectType[] findDeclaredExceptions(InvokeInstruction inv, ConstantPoolGen cpg) {
        return Hierarchy2.findDeclaredExceptions(inv, cpg);
    }

    /**
     * Find a method in given class.
     *
     * @param javaClass
     *            the class
     * @param methodName
     *            the name of the method
     * @param methodSig
     *            the signature of the method
     * @return the JavaClassAndMethod, or null if no such method exists in the
     *         class
     */
    public static @CheckForNull
    JavaClassAndMethod findMethod(JavaClass javaClass, String methodName, String methodSig) {
        return findMethod(javaClass, methodName, methodSig, ANY_METHOD);
    }

    public static @CheckForNull
    JavaClassAndMethod findMethod(JavaClass javaClass, String methodName, String methodSig, JavaClassAndMethodChooser chooser) {
        if (DEBUG_METHOD_LOOKUP) {
            System.out.println("Check " + javaClass.getClassName());
        }
        Method[] methodList = javaClass.getMethods();
        for (Method method : methodList) {
            if (method.getName().equals(methodName) && method.getSignature().equals(methodSig)) {
                JavaClassAndMethod m = new JavaClassAndMethod(javaClass, method);
                if (chooser.choose(m)) {
                    if (DEBUG_METHOD_LOOKUP) {
                        System.out.println("\t==> FOUND: " + method);
                    }
                    return m;
                }
            }
        }
        if (DEBUG_METHOD_LOOKUP) {
            System.out.println("\t==> NOT FOUND");
        }
        return null;
    }

    /**
     * Find a method in given class.
     *
     * @param classDesc
     *            the class descriptor
     * @param methodName
     *            the name of the method
     * @param methodSig
     *            the signature of the method
     * @param isStatic
     *            are we looking for a static method?
     * @return the JavaClassAndMethod, or null if no such method exists in the
     *         class
     */
    public static @CheckForNull
    XMethod findMethod(ClassDescriptor classDesc, String methodName, String methodSig, boolean isStatic) {
        if (DEBUG_METHOD_LOOKUP) {
            System.out.println("Check " + classDesc.getClassName());
        }

        try {
            XClass xClass = Global.getAnalysisCache().getClassAnalysis(XClass.class, classDesc);
            return xClass.findMethod(methodName, methodSig, isStatic);
        } catch (CheckedAnalysisException e) {
            AnalysisContext.logError("Error looking for " + classDesc + "." + methodName + methodSig, e);
            return null;
        }

    }

    /**
     * Find a method in given class.
     *
     * @param javaClass
     *            the class
     * @param methodName
     *            the name of the method
     * @param methodSig
     *            the signature of the method
     * @return the JavaClassAndMethod, or null if no such method exists in the
     *         class
     */
    @Deprecated
    public static @CheckForNull
    JavaClassAndMethod findConcreteMethod(JavaClass javaClass, String methodName, String methodSig) {

        if (DEBUG_METHOD_LOOKUP) {
            System.out.println("Check " + javaClass.getClassName());
        }
        Method[] methodList = javaClass.getMethods();
        for (Method method : methodList) {
            if (method.getName().equals(methodName) && method.getSignature().equals(methodSig)
                    && accessFlagsAreConcrete(method.getAccessFlags())) {
                JavaClassAndMethod m = new JavaClassAndMethod(javaClass, method);

                return m;

            }
        }
        if (DEBUG_METHOD_LOOKUP) {
            System.out.println("\t==> NOT FOUND");
        }
        return null;
    }

    /**
     * Find a method in given class.
     *
     * @param javaClass
     *            the class
     * @param methodName
     *            the name of the method
     * @param methodSig
     *            the signature of the method
     * @param chooser
     *            the JavaClassAndMethodChooser to use to screen possible
     *            candidates
     * @return the XMethod, or null if no such method exists in the class
     */
    @Deprecated
    public static @CheckForNull
    XMethod findXMethod(JavaClass javaClass, String methodName, String methodSig, JavaClassAndMethodChooser chooser) {
        JavaClassAndMethod result = findMethod(javaClass, methodName, methodSig, chooser);
        return result == null ? null : XFactory.createXMethod(result.getJavaClass(), result.getMethod());
    }

    /**
     * JavaClassAndMethodChooser which accepts any method.
     */
    public static final JavaClassAndMethodChooser ANY_METHOD = new JavaClassAndMethodChooser() {
        @Override
        public boolean choose(JavaClassAndMethod javaClassAndMethod) {
            return true;
        }

        @Override
        public boolean choose(XMethod method) {
            return true;
        }

    };

    // FIXME: perhaps native methods should be concrete.
    public static boolean accessFlagsAreConcrete(int accessFlags) {
        return (accessFlags & Constants.ACC_ABSTRACT) == 0 && (accessFlags & Constants.ACC_NATIVE) == 0;
    }

    /**
     * JavaClassAndMethodChooser which accepts only concrete (not abstract or
     * native) methods.
     */
    public static final JavaClassAndMethodChooser CONCRETE_METHOD = new JavaClassAndMethodChooser() {
        @Override
        public boolean choose(JavaClassAndMethod javaClassAndMethod) {
            Method method = javaClassAndMethod.getMethod();
            int accessFlags = method.getAccessFlags();
            return accessFlagsAreConcrete(accessFlags);
        }

        @Override
        public boolean choose(XMethod method) {
            return accessFlagsAreConcrete(method.getAccessFlags());
        }
    };

    /**
     * JavaClassAndMethodChooser which accepts only static methods.
     */
    public static final JavaClassAndMethodChooser STATIC_METHOD = new JavaClassAndMethodChooser() {
        @Override
        public boolean choose(JavaClassAndMethod javaClassAndMethod) {
            return javaClassAndMethod.getMethod().isStatic();
        }

        @Override
        public boolean choose(XMethod method) {
            return method.isStatic();
        }
    };

    /**
     * JavaClassAndMethodChooser which accepts only instance methods.
     */
    public static final JavaClassAndMethodChooser INSTANCE_METHOD = new JavaClassAndMethodChooser() {
        @Override
        public boolean choose(JavaClassAndMethod javaClassAndMethod) {
            return !javaClassAndMethod.getMethod().isStatic();
        }

        @Override
        public boolean choose(XMethod method) {
            return !method.isStatic();
        }
    };

    /**
     * Find a method in given list of classes, searching the classes in order.
     *
     * @param classList
     *            list of classes in which to search
     * @param methodName
     *            the name of the method
     * @param methodSig
     *            the signature of the method
     * @return the JavaClassAndMethod, or null if no such method exists in the
     *         class
     */
    @Deprecated
    public static JavaClassAndMethod findMethod(JavaClass[] classList, String methodName, String methodSig) {
        return findMethod(classList, methodName, methodSig, ANY_METHOD);
    }

    /**
     * Find a method in given list of classes, searching the classes in order.
     *
     * @param classList
     *            list of classes in which to search
     * @param methodName
     *            the name of the method
     * @param methodSig
     *            the signature of the method
     * @param chooser
     *            JavaClassAndMethodChooser to select which methods are
     *            considered; it must return true for a method to be returned
     * @return the JavaClassAndMethod, or null if no such method exists in the
     *         class
     */
    public static JavaClassAndMethod findMethod(JavaClass[] classList, String methodName, String methodSig,
            JavaClassAndMethodChooser chooser) {
        JavaClassAndMethod m = null;

        for (JavaClass cls : classList) {
            if ((m = findMethod(cls, methodName, methodSig, chooser)) != null) {
                break;
            }
        }

        return m;
    }

    /**
     * Find XMethod for method in given list of classes, searching the classes
     * in order.
     *
     * @param classList
     *            list of classes in which to search
     * @param methodName
     *            the name of the method
     * @param methodSig
     *            the signature of the method
     * @return the XMethod, or null if no such method exists in the class
     */
    @Deprecated
    public static XMethod findXMethod(JavaClass[] classList, String methodName, String methodSig) {
        return findXMethod(classList, methodName, methodSig, ANY_METHOD);
    }

    /**
     * Find XMethod for method in given list of classes, searching the classes
     * in order.
     *
     * @param classList
     *            list of classes in which to search
     * @param methodName
     *            the name of the method
     * @param methodSig
     *            the signature of the method
     * @param chooser
     *            JavaClassAndMethodChooser to select which methods are
     *            considered; it must return true for a method to be returned
     * @return the XMethod, or null if no such method exists in the class
     */
    @Deprecated
    public static XMethod findXMethod(JavaClass[] classList, String methodName, String methodSig,
            JavaClassAndMethodChooser chooser) {
        for (JavaClass cls : classList) {
            JavaClassAndMethod m;
            if ((m = findMethod(cls, methodName, methodSig)) != null && chooser.choose(m)) {
                return XFactory.createXMethod(cls, m.getMethod());
            }
        }
        return null;
    }

    /**
     * Resolve possible method call targets. This works for both static and
     * instance method calls.
     *
     * @param invokeInstruction
     *            the InvokeInstruction
     * @param typeFrame
     *            the TypeFrame containing the types of stack values
     * @param cpg
     *            the ConstantPoolGen
     * @return Set of methods which might be called
     * @throws DataflowAnalysisException
     * @throws ClassNotFoundException
     */
    public static Set<JavaClassAndMethod> resolveMethodCallTargets(InvokeInstruction invokeInstruction, TypeFrame typeFrame,
            ConstantPoolGen cpg) throws DataflowAnalysisException, ClassNotFoundException {

        short opcode = invokeInstruction.getOpcode();

        if (opcode == Constants.INVOKESTATIC) {
            HashSet<JavaClassAndMethod> result = new HashSet<JavaClassAndMethod>();
            JavaClassAndMethod targetMethod = findInvocationLeastUpperBound(invokeInstruction, cpg, CONCRETE_METHOD);
            if (targetMethod != null) {
                result.add(targetMethod);
            }
            return result;
        }

        if (!typeFrame.isValid()) {
            return new HashSet<JavaClassAndMethod>();
        }

        Type receiverType;
        boolean receiverTypeIsExact;

        if (opcode == Constants.INVOKESPECIAL) {
            // invokespecial instructions are dispatched to EXACTLY
            // the class specified by the instruction
            receiverType = ObjectTypeFactory.getInstance(invokeInstruction.getClassName(cpg));
            receiverTypeIsExact = false; // Doesn't actually matter
        } else {
            // For invokevirtual and invokeinterface instructions, we have
            // virtual dispatch. By taking the receiver type (which may be a
            // subtype of the class specified by the instruction),
            // we may get a more precise set of call targets.
            int instanceStackLocation = typeFrame.getInstanceStackLocation(invokeInstruction, cpg);
            receiverType = typeFrame.getStackValue(instanceStackLocation);
            if (!(receiverType instanceof ReferenceType)) {
                return new HashSet<JavaClassAndMethod>();
            }
            receiverTypeIsExact = typeFrame.isExact(instanceStackLocation);
        }
        if (DEBUG_METHOD_LOOKUP) {
            System.out.println("[receiver type is " + receiverType + ", " + (receiverTypeIsExact ? "exact]" : " not exact]"));
        }

        return resolveMethodCallTargets((ReferenceType) receiverType, invokeInstruction, cpg, receiverTypeIsExact);
    }

    /**
     * Resolve possible instance method call targets. Assumes that invokevirtual
     * and invokeinterface methods may call any subtype of the receiver class.
     *
     * @param receiverType
     *            type of the receiver object
     * @param invokeInstruction
     *            the InvokeInstruction
     * @param cpg
     *            the ConstantPoolGen
     * @return Set of methods which might be called
     * @throws ClassNotFoundException
     */
    public static Set<JavaClassAndMethod> resolveMethodCallTargets(ReferenceType receiverType,
            InvokeInstruction invokeInstruction, ConstantPoolGen cpg) throws ClassNotFoundException {
        return resolveMethodCallTargets(receiverType, invokeInstruction, cpg, false);
    }

    /**
     * Resolve possible instance method call targets.
     *
     * @param receiverType
     *            type of the receiver object
     * @param invokeInstruction
     *            the InvokeInstruction
     * @param cpg
     *            the ConstantPoolGen
     * @param receiverTypeIsExact
     *            if true, the receiver type is known exactly, which should
     *            allow a precise result
     * @return Set of methods which might be called
     * @throws ClassNotFoundException
     */
    public static Set<JavaClassAndMethod> resolveMethodCallTargets(ReferenceType receiverType,
            InvokeInstruction invokeInstruction, ConstantPoolGen cpg, boolean receiverTypeIsExact) throws ClassNotFoundException {
        HashSet<JavaClassAndMethod> result = new HashSet<JavaClassAndMethod>();

        if (invokeInstruction.getOpcode() == Constants.INVOKESTATIC) {
            throw new IllegalArgumentException();
        }

        String methodName = invokeInstruction.getName(cpg);
        String methodSig = invokeInstruction.getSignature(cpg);

        // Array method calls aren't virtual.
        // They should just resolve to Object methods.
        if (receiverType instanceof ArrayType) {
            JavaClass javaLangObject = AnalysisContext.currentAnalysisContext().lookupClass("java.lang.Object");
            JavaClassAndMethod classAndMethod = findMethod(javaLangObject, methodName, methodSig, INSTANCE_METHOD);
            if (classAndMethod != null) {
                result.add(classAndMethod);
            }
            return result;
        }

        if (receiverType instanceof NullType) {
            return Collections.<JavaClassAndMethod> emptySet();
        }
        AnalysisContext analysisContext = AnalysisContext.currentAnalysisContext();

        // Get the receiver class.
        String receiverClassName = ((ObjectType) receiverType).getClassName();
        JavaClass receiverClass = analysisContext.lookupClass(receiverClassName);
        ClassDescriptor receiverDesc = DescriptorFactory.createClassDescriptorFromDottedClassName(receiverClassName);

        // Figure out the upper bound for the method.
        // This is what will be called if this is not a virtual call site.
        JavaClassAndMethod upperBound = findMethod(receiverClass, methodName, methodSig, CONCRETE_METHOD);
        if (upperBound == null) {
            upperBound = findInvocationLeastUpperBound(receiverClass, methodName, methodSig, CONCRETE_METHOD, false);
        }
        if (upperBound != null) {
            if (DEBUG_METHOD_LOOKUP) {
                System.out.println("Adding upper bound: "
                        + SignatureConverter.convertMethodSignature(upperBound.getJavaClass(), upperBound.getMethod()));
            }
            result.add(upperBound);
        }

        // Is this a virtual call site?
        boolean virtualCall = (invokeInstruction.getOpcode() == Constants.INVOKEVIRTUAL || invokeInstruction.getOpcode() == Constants.INVOKEINTERFACE)
                && (upperBound == null || !upperBound.getJavaClass().isFinal() && !upperBound.getMethod().isFinal())
                && !receiverTypeIsExact;

        if (virtualCall) {
            if (!"java.lang.Object".equals(receiverClassName)) {

                // This is a true virtual call: assume that any concrete
                // subtype method may be called.
                Set<ClassDescriptor> subTypeSet = analysisContext.getSubtypes2().getSubtypes(receiverDesc);
                for (ClassDescriptor subtype : subTypeSet) {
                    XMethod concreteSubtypeMethod = findMethod(subtype, methodName, methodSig, false);
                    if (concreteSubtypeMethod != null && (concreteSubtypeMethod.getAccessFlags() & Constants.ACC_ABSTRACT) == 0) {
                        result.add(new JavaClassAndMethod(concreteSubtypeMethod));
                    }
                }
                if (false && subTypeSet.size() > 500) {
                    new RuntimeException(receiverClassName + " has " + subTypeSet.size() + " subclasses, " + result.size()
                            + " of which implement " + methodName + methodSig + " " + invokeInstruction)
                    .printStackTrace(System.out);
                }

            }
        }
        return result;
    }

    /**
     * Return whether or not the given method is concrete.
     *
     * @param xmethod
     *            the method
     * @return true if the method is concrete, false otherwise
     */
    @Deprecated
    public static boolean isConcrete(XMethod xmethod) {
        int accessFlags = xmethod.getAccessFlags();
        return (accessFlags & Constants.ACC_ABSTRACT) == 0 && (accessFlags & Constants.ACC_NATIVE) == 0;
    }

    /**
     * Find a field with given name defined in given class.
     *
     * @param className
     *            the name of the class
     * @param fieldName
     *            the name of the field
     * @return the Field, or null if no such field could be found
     */
    public static Field findField(String className, String fieldName) throws ClassNotFoundException {
        JavaClass jclass = Repository.lookupClass(className);

        while (jclass != null) {
            Field[] fieldList = jclass.getFields();
            for (Field field : fieldList) {
                if (field.getName().equals(fieldName)) {
                    return field;
                }
            }

            jclass = jclass.getSuperClass();
        }

        return null;
    }

    /**
     * Look up a field with given name and signature in given class, returning
     * it as an {@link XField XField} object. If a field can't be found in the
     * immediate class, its superclass is search, and so forth.
     *
     * @param className
     *            name of the class through which the field is referenced
     * @param fieldName
     *            name of the field
     * @param fieldSig
     *            signature of the field
     * @param isStatic
     *            true if field is static, false otherwise
     * @return an XField object representing the field, or null if no such field
     *         could be found
     */
    public static XField findXField(String className, String fieldName, String fieldSig, boolean isStatic)
    {

        return XFactory.createXField(className, fieldName, fieldSig, isStatic);
    }

    /**
     * Look up the field referenced by given FieldInstruction, returning it as
     * an {@link XField XField} object.
     *
     * @param fins
     *            the FieldInstruction
     * @param cpg
     *            the ConstantPoolGen used by the class containing the
     *            instruction
     * @return an XField object representing the field, or null if no such field
     *         could be found
     */
    public static @CheckForNull XField findXField(FieldInstruction fins, @Nonnull ConstantPoolGen cpg) {

        String className = fins.getClassName(cpg);
        String fieldName = fins.getFieldName(cpg);
        String fieldSig = fins.getSignature(cpg);

        boolean isStatic = (fins.getOpcode() == Constants.GETSTATIC || fins.getOpcode() == Constants.PUTSTATIC);

        XField xfield = findXField(className, fieldName, fieldSig, isStatic);
        short opcode = fins.getOpcode();
        if (xfield != null && xfield.isResolved()
                && xfield.isStatic() == (opcode == Constants.GETSTATIC || opcode == Constants.PUTSTATIC)) {
            return xfield;
        } else {
            return null;
        }
    }

    /**
     * Determine whether the given INVOKESTATIC instruction is an inner-class
     * field accessor method.
     *
     * @param inv
     *            the INVOKESTATIC instruction
     * @param cpg
     *            the ConstantPoolGen for the method
     * @return true if the instruction is an inner-class field accessor, false
     *         if not
     */
    public static boolean isInnerClassAccess(INVOKESTATIC inv, ConstantPoolGen cpg) {
        String methodName = inv.getName(cpg);
        return methodName.startsWith("access$");
    }

    /**
     * Get the InnerClassAccess for access method called by given INVOKESTATIC.
     *
     * @param inv
     *            the INVOKESTATIC instruction
     * @param cpg
     *            the ConstantPoolGen for the method
     * @return the InnerClassAccess, or null if the instruction is not an
     *         inner-class access
     */
    public static InnerClassAccess getInnerClassAccess(INVOKESTATIC inv, ConstantPoolGen cpg) throws ClassNotFoundException {

        String className = inv.getClassName(cpg);
        String methodName = inv.getName(cpg);
        String methodSig = inv.getSignature(cpg);

        InnerClassAccess access = AnalysisContext.currentAnalysisContext().getInnerClassAccessMap()
                .getInnerClassAccess(className, methodName);
        return (access != null && access.getMethodSignature().equals(methodSig)) ? access : null;
    }

}

