edu.umd.cs.findbugs.ba

Class Frame<ValueType>

java.lang.Object

edu.umd.cs.findbugs.ba.Frame<ValueType>

Direct Known Subclasses:

ConstantFrame, IsNullValueFrame, ResourceValueFrame, TypeFrame, ValueNumberFrame

public abstract class Frame<ValueType>
extends java.lang.Object

Generic class for representing a Java stack frame as a dataflow value. A frame consists of "slots", which represent the local variables and values on the Java operand stack. Slots 0 .. getNumLocals() - 1 represent the local variables. Slots getNumLocals() .. getNumSlots() - 1 represent the Java operand stack.

Frame is parametized by "ValueType", which is the type of value to be stored in the Frame's slots. This type must form a lattice, according to the abstract mergeValues() operation in the corresponding analysis class (which should be derived from FrameDataflowAnalysis). When a Frame is constructed, all of its slots will contain null. The analysis is responsible for initializing created Frames with default values at the appropriate time. Typically, only initEntryFact() will need to do this.

A Frame may have the special "TOP" value. Such frames serve as the identity element for the meet operation operation.

A Frame may have the special "BOTTOM" value. The result of merging any frame with BOTTOM is BOTTOM.

Author:

David Hovemeyer

See Also:

FrameDataflowAnalysis

Constructor Summary

Constructors

Constructor and Description
Frame(int numLocals) Constructor.

Method Summary

Methods

Modifier and Type	Method and Description
java.util.Collection<ValueType>	allSlots()
void	clearStack() Clear the Java operand stack.
boolean	contains(ValueType value)
void	copyFrom(Frame<ValueType> other) Make this Frame exactly the same as the one given as a parameter.
ValueType	getArgument(org.apache.bcel.generic.InvokeInstruction ins, org.apache.bcel.generic.ConstantPoolGen cpg, int i, int numArguments) Deprecated.
ValueType	getArgument(org.apache.bcel.generic.InvokeInstruction ins, org.apache.bcel.generic.ConstantPoolGen cpg, int i, SignatureParser sigParser) Get the ith argument passed to given method invocation.
java.util.BitSet	getArgumentSet(org.apache.bcel.generic.InvokeInstruction invokeInstruction, org.apache.bcel.generic.ConstantPoolGen cpg, DataflowValueChooser<ValueType> chooser) Get set of arguments passed to a method invocation which match given predicate.
int	getArgumentSlot(int i, int numArguments) Get the stack slot that will contain given method argument.
ValueType	getInstance(org.apache.bcel.generic.Instruction ins, org.apache.bcel.generic.ConstantPoolGen cpg) Get the value corresponding to the object instance used in the given instruction.
int	getInstanceSlot(org.apache.bcel.generic.Instruction ins, org.apache.bcel.generic.ConstantPoolGen cpg) Get the slot the object instance referred to by given instruction is located in.
int	getInstanceStackLocation(org.apache.bcel.generic.Instruction ins, org.apache.bcel.generic.ConstantPoolGen cpg) Get the stack location (counting down from top of stack, starting at 0) containing the object instance referred to by given instruction.
int	getLastUpdateTimestamp()
int	getNumArguments(org.apache.bcel.generic.InvokeInstruction ins, org.apache.bcel.generic.ConstantPoolGen cpg) Get the number of arguments passed to given method invocation.
int	getNumArgumentsIncludingObjectInstance(org.apache.bcel.generic.InvokeInstruction ins, org.apache.bcel.generic.ConstantPoolGen cpg) Get the number of arguments passed to given method invocation, including the object instance if the call is to an instance method.
int	getNumLocals() Get the number of locals.
int	getNumSlots() Get the number of slots (locals plus stack values).
ValueType	getOperand(org.apache.bcel.generic.StackConsumer ins, org.apache.bcel.generic.ConstantPoolGen cpg, int i) Get the ith operand used by given instruction.
int	getStackDepth() Get the depth of the Java operand stack.
int	getStackLocation(int loc) Get a the location in the frame of a value on the operand stack.
ValueType	getStackValue(int loc) Get a value on the operand stack.
void	getTopStackWords(ValueType[] valueList) Get the values on the top of the Java operand stack.
ValueType	getTopValue() Get the value on the top of the Java operand stack.
ValueType	getValue(int n) Get the value at the nth slot.
boolean	isBottom() Return whether or not this object is the special "BOTTOM" value for Frames.
boolean	isTop() Return whether or not this object the special "TOP" value for Frames.
boolean	isValid() Is the frame valid (meaning it is not TOP or BOTTOM)?
ValueType	popValue() Pop a value off of the Java operand stack.
void	pushValue(ValueType value) Push a value onto the Java operand stack.
boolean	sameAs(Frame<ValueType> other) Return true if this stack frame is the same as the one given as a parameter.
void	setBottom() Make this Frame the special "BOTTOM" value.
void	setLastUpdateTimestamp(int lastUpdateTimestamp)
void	setTop() Make this frame the special "TOP" value.
void	setValid() Set the Frame to be valid (neither TOP nor BOTTOM).
void	setValue(int n, ValueType value) Set the value at the nth slot.
java.lang.String	toString() Convert to string.
protected java.lang.String	valueToString(ValueType value) Subclasses may override this if they want to do something special to convert Value objects to Strings.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

Frame

public Frame(int numLocals)

Constructor. This version of the constructor is for subclasses for which it is always safe to call getDefaultValue(), even when the object is not fully initialized.

Parameters:

numLocals - number of local variable slots in the method

Method Detail

isTop

public boolean isTop()

Return whether or not this object the special "TOP" value for Frames. Such Frames are the identity element of the meet operation.

setTop

public void setTop()

Make this frame the special "TOP" value. Such Frames are the identity element of the meet operation.

isBottom

public boolean isBottom()

Return whether or not this object is the special "BOTTOM" value for Frames. Such Frames arise when merging two frames of different size.

setBottom

public void setBottom()

Make this Frame the special "BOTTOM" value. Such Frames arise when merging two frames of different size.

setValid

public void setValid()

Set the Frame to be valid (neither TOP nor BOTTOM).

isValid

public boolean isValid()

Is the frame valid (meaning it is not TOP or BOTTOM)?

pushValue

public void pushValue(ValueType value)

Push a value onto the Java operand stack.

Parameters:

value - the ValueType to push

popValue

public ValueType popValue()
                   throws DataflowAnalysisException

Pop a value off of the Java operand stack.

Returns:

the value that was popped

Throws:

DataflowAnalysisException - if the Java operand stack is empty

getTopValue

public ValueType getTopValue()
                      throws DataflowAnalysisException

Get the value on the top of the Java operand stack.

Throws:

DataflowAnalysisException - if the Java operand stack is empty

getTopStackWords

public void getTopStackWords(ValueType[] valueList)
                      throws DataflowAnalysisException

Get the values on the top of the Java operand stack. The top stack item is placed at the end of the array, so that to restore the values to the stack, you would push them in the order they appear in the array.

Throws:

DataflowAnalysisException

getStackValue

public ValueType getStackValue(int loc)
                        throws DataflowAnalysisException

Get a value on the operand stack.

Parameters:

loc - the stack location, counting downwards from the top (location 0)

Throws:

DataflowAnalysisException

getStackLocation

public int getStackLocation(int loc)
                     throws DataflowAnalysisException

Get a the location in the frame of a value on the operand stack.

Parameters:

loc - the stack location, counting downwards from the top (location 0)

Throws:

DataflowAnalysisException

getInstance

public ValueType getInstance(org.apache.bcel.generic.Instruction ins,
                    org.apache.bcel.generic.ConstantPoolGen cpg)
                      throws DataflowAnalysisException

Get the value corresponding to the object instance used in the given instruction. This relies on the observation that in instructions which use an object instance (such as getfield, invokevirtual, etc.), the object instance is the first operand used by the instruction.

Parameters:

ins - the instruction

cpg - the ConstantPoolGen for the method

Throws:

DataflowAnalysisException

getInstanceStackLocation

public int getInstanceStackLocation(org.apache.bcel.generic.Instruction ins,
                           org.apache.bcel.generic.ConstantPoolGen cpg)
                             throws DataflowAnalysisException

Get the stack location (counting down from top of stack, starting at 0) containing the object instance referred to by given instruction. This relies on the observation that in instructions which use an object instance (such as getfield, invokevirtual, etc.), the object instance is the first operand used by the instruction.

The value returned may be passed to getStackValue(int).

Parameters:

ins - the Instruction

cpg - the ConstantPoolGen for the method

Returns:

stack location (counting down from top of stack, starting at 0) containing the object instance

Throws:

DataflowAnalysisException

getInstanceSlot

public int getInstanceSlot(org.apache.bcel.generic.Instruction ins,
                  org.apache.bcel.generic.ConstantPoolGen cpg)
                    throws DataflowAnalysisException

Get the slot the object instance referred to by given instruction is located in.

Parameters:

ins - the Instruction

cpg - the ConstantPoolGen for the method

Returns:

stack slot the object instance is in

Throws:

DataflowAnalysisException

getNumArguments

public int getNumArguments(org.apache.bcel.generic.InvokeInstruction ins,
                  org.apache.bcel.generic.ConstantPoolGen cpg)

Get the number of arguments passed to given method invocation.

Parameters:

ins - the method invocation instruction

cpg - the ConstantPoolGen for the class containing the method

Returns:

number of arguments; note that this excludes the object instance for instance methods

getNumArgumentsIncludingObjectInstance

public int getNumArgumentsIncludingObjectInstance(org.apache.bcel.generic.InvokeInstruction ins,
                                         org.apache.bcel.generic.ConstantPoolGen cpg)
                                           throws DataflowAnalysisException

Get the number of arguments passed to given method invocation, including the object instance if the call is to an instance method.

Parameters:

ins - the method invocation instruction

cpg - the ConstantPoolGen for the class containing the method

Returns:

number of arguments, including object instance if appropriate

Throws:

DataflowAnalysisException

getArgument

@Deprecated
public ValueType getArgument(org.apache.bcel.generic.InvokeInstruction ins,
                               org.apache.bcel.generic.ConstantPoolGen cpg,
                               int i,
                               int numArguments)
                      throws DataflowAnalysisException

Deprecated.

Get the ith argument passed to given method invocation.

Parameters:

ins - the method invocation instruction

cpg - the ConstantPoolGen for the class containing the method

i - index of the argument; 0 for the first argument, etc.

numArguments - total number of arguments to the method

Returns:

the ith argument

Throws:

DataflowAnalysisException

getArgument

public ValueType getArgument(org.apache.bcel.generic.InvokeInstruction ins,
                    org.apache.bcel.generic.ConstantPoolGen cpg,
                    int i,
                    SignatureParser sigParser)
                      throws DataflowAnalysisException

Get the ith argument passed to given method invocation.

Parameters:

ins - the method invocation instruction

cpg - the ConstantPoolGen for the class containing the method

i - index of the argument; 0 for the first argument, etc.

Returns:

the ith argument

Throws:

DataflowAnalysisException

getArgumentSlot

public int getArgumentSlot(int i,
                  int numArguments)

Get the stack slot that will contain given method argument. Assumes that this frame is at the location (just before) a method invocation instruction.

Parameters:

i - the argument index: 0 for first arg, etc.

numArguments - total number of arguments to the called method

Returns:

slot containing the argument value

getOperand

public ValueType getOperand(org.apache.bcel.generic.StackConsumer ins,
                   org.apache.bcel.generic.ConstantPoolGen cpg,
                   int i)
                     throws DataflowAnalysisException

Get the ith operand used by given instruction.

Parameters:

ins - the instruction, which must be a StackConsumer

cpg - the ConstantPoolGen

i - index of operand to get: 0 for the first operand, etc.

Returns:

the ith operand used by the given instruction

Throws:

DataflowAnalysisException

getArgumentSet

public java.util.BitSet getArgumentSet(org.apache.bcel.generic.InvokeInstruction invokeInstruction,
                              org.apache.bcel.generic.ConstantPoolGen cpg,
                              DataflowValueChooser<ValueType> chooser)
                                throws DataflowAnalysisException

Get set of arguments passed to a method invocation which match given predicate.

Parameters:

invokeInstruction - the InvokeInstruction

cpg - the ConstantPoolGen

chooser - predicate to choose which argument values should be in the returned set

Returns:

BitSet specifying which arguments match the predicate, indexed by argument number (starting from 0)

Throws:

DataflowAnalysisException

clearStack

public void clearStack()

Clear the Java operand stack. Only local variable slots will remain in the frame.

getStackDepth

public int getStackDepth()

Get the depth of the Java operand stack.

getNumLocals

public int getNumLocals()

Get the number of locals.

getNumSlots

public int getNumSlots()

Get the number of slots (locals plus stack values).

contains

public boolean contains(ValueType value)

getValue

public ValueType getValue(int n)

Get the value at the nth slot.

Parameters:

n - the slot to get the value of

Returns:

the value in the slot

setValue

public void setValue(int n,
            ValueType value)

Set the value at the nth slot.

Parameters:

n - the slot in which to set a new value

value - the value to set

sameAs

public boolean sameAs(Frame<ValueType> other)

Return true if this stack frame is the same as the one given as a parameter.

Parameters:

other - the other Frame

Returns:

true if the frames are the same, false otherwise

copyFrom

public void copyFrom(Frame<ValueType> other)

Make this Frame exactly the same as the one given as a parameter.

Parameters:

other - the Frame to make this object the same as

toString

public java.lang.String toString()

Convert to string.

Overrides:

toString in class java.lang.Object

valueToString

protected java.lang.String valueToString(ValueType value)

Subclasses may override this if they want to do something special to convert Value objects to Strings. By default, we just call toString() on the values.

allSlots

public java.util.Collection<ValueType> allSlots()

Returns:

an unmodifiable Collection of the local variable and operand stack slots

setLastUpdateTimestamp

public void setLastUpdateTimestamp(int lastUpdateTimestamp)

Parameters:

lastUpdateTimestamp - The lastUpdateTimestamp to set.

getLastUpdateTimestamp

public int getLastUpdateTimestamp()

Returns:

Returns the lastUpdateTimestamp.