FindBugs™ 1.3.9

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

java.lang.Object
  extended by 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
Frame(int numLocals)
          Constructor.
 
Method Summary
 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)
                    throws DataflowAnalysisException
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
Throws:
DataflowAnalysisException

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.

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