com.sun.jdi
Interface StackFrame

All Superinterfaces:

Locatable, Mirror

public interface StackFrame

extends Mirror, Locatable

The state of one method invocation on a thread's call stack. As a thread executes, stack frames are pushed and popped from its call stack as methods are invoked and then return. A StackFrame mirrors one such frame from a target VM at some point in its thread's execution. The call stack is, then, simply a List of StackFrame objects. The call stack can be obtained any time a thread is suspended through a call to ThreadReference.frames()

StackFrames provide access to a method's local variables and their current values.

The lifetime of a StackFrame is very limited. It is available only for suspended threads and becomes invalid once its thread is resumed.

Since:

1.3

Method Summary

Value	getValue(LocalVariable variable) Gets the Value of a LocalVariable in this frame.
Map	getValues(List variables) Returns the values of multiple local variables in this frame.
Location	location() Returns the Location of the current instruction in the frame.
void	setValue(LocalVariable variable, Value value) Sets the Value of a LocalVariable in this frame.
ObjectReference	thisObject() Returns the value of 'this' for the current frame.
ThreadReference	thread() Returns the thread under which this frame's method is running.
LocalVariable	visibleVariableByName(String name) Finds a LocalVariable that matches the given name and is visible at the current frame location.
List	visibleVariables() Returns a list containing each LocalVariable that can be accessed from this frame's location.

Methods inherited from interface com.sun.jdi.Mirror

toString, virtualMachine

Method Detail

location

public Location location()

Returns the Location of the current instruction in the frame. The method for which this frame was created can also be accessed through the returned location. For the top frame in the stack, this location identifies the next instruction to be executed. For all other frames, this location identifies the instruction that caused the next frame's method to be invoked. If the frame represents a native method invocation, the returned location indicates the class and method, but the code index will not be valid.

Specified by:

location in interface Locatable

Returns:

the Location of the current instruction.

Throws:

InvalidStackFrameException - if this stack frame has become invalid. Once the frame's thread is resumed, the stack frame is no longer valid.

thread

public ThreadReference thread()

Returns the thread under which this frame's method is running.

Returns:

a ThreadReference which mirrors the frame's thread.

Throws:

InvalidStackFrameException - if this stack frame has become invalid. Once the frame's thread is resumed, the stack frame is no longer valid.

thisObject

public ObjectReference thisObject()

Returns the value of 'this' for the current frame. The ObjectReference for 'this' is only available for non-native instance methods.

Returns:

an ObjectReference, or null if the frame represents a native or static method.

Throws:

InvalidStackFrameException - if this stack frame has become invalid. Once the frame's thread is resumed, the stack frame is no longer valid.

visibleVariables

public List visibleVariables()
                      throws AbsentInformationException

Returns a list containing each LocalVariable that can be accessed from this frame's location.

Visibility is based on the code index of the current instruction of this StackFrame. Each variable has a range of byte code indices in which it is accessible. If this stack frame's method matches this variable's method and if the code index of this StackFrame is within the variable's byte code range, the variable is visible.

A variable's byte code range is at least as large as the scope of that variable, but can continue beyond the end of the scope under certain circumstances:

• the compiler/VM does not immediately reuse the variable's slot.
• the compiler/VM is implemented to report the extended range that would result from the item above.

The advantage of an extended range is that variables from recently exited scopes may remain available for examination (this is especially useful for loop indices). If, as a result of the extensions above, the current frame location is contained within the range of multiple local variables of the same name, the variable with the highest-starting range is chosen for the returned list.

Returns:

the list of LocalVariable objects currently visible.

Throws:

AbsentInformationException - if there is no line number information for this method.

InvalidStackFrameException - if this stack frame has become invalid. Once the frame's thread is resumed, the stack frame is no longer valid.

visibleVariableByName

public LocalVariable visibleVariableByName(String name)
                                    throws AbsentInformationException

Finds a LocalVariable that matches the given name and is visible at the current frame location. See visibleVariables() for more information on visibility.

Parameters:

name - the variable name to find

Returns:

the matching LocalVariable, or null if there is no visible variable with the given name.

Throws:

AbsentInformationException - if there is no line number information for this method.

InvalidStackFrameException - if this stack frame has become invalid. Once the frame's thread is resumed, the stack frame is no longer valid.

getValue

public Value getValue(LocalVariable variable)

Gets the Value of a LocalVariable in this frame. The variable must be valid for this frame's method and visible according to the rules described in visibleVariables().

Parameters:

variable - the LocalVariable to be accessed

Returns:

the Value of the instance field.

Throws:

IllegalArgumentException - if the variable is either invalid for this frame's method or not visible.

InvalidStackFrameException - if this stack frame has become invalid. Once the frame's thread is resumed, the stack frame is no longer valid.

VMMismatchException - if a Mirror argument and this mirror do not belong to the same VirtualMachine.

getValues

public Map getValues(List variables)

Returns the values of multiple local variables in this frame. Each variable must be valid for this frame's method and visible according to the rules described in visibleVariables().

Parameters:

variables - a list of LocalVariable objects to be accessed

Returns:

a map associating each LocalVariable with its Value

Throws:

IllegalArgumentException - if any variable is either invalid for this frame's method or not visible.

InvalidStackFrameException - if this stack frame has become invalid. Once the frame's thread is resumed, the stack frame is no longer valid.

VMMismatchException - if a Mirror argument and this mirror do not belong to the same VirtualMachine.

setValue

public void setValue(LocalVariable variable,
                     Value value)
              throws InvalidTypeException,
                     ClassNotLoadedException

Sets the Value of a LocalVariable in this frame. The variable must be valid for this frame's method and visible according to the rules described in visibleVariables().

Object values must be assignment compatible with the variable type (This implies that the variable type must be loaded through the enclosing class's class loader). Primitive values must be either assignment compatible with the variable type or must be convertible to the variable type without loss of information. See JLS section 5.2 for more information on assignment compatibility.

Parameters:

variable - the field containing the requested value

value - the new value to assign

Throws:

IllegalArgumentException - if the field is not valid for this object's class.

InvalidTypeException - if the value's type does not match the variable's type.

ClassNotLoadedException - if the variable type has not yet been loaded through the appropriate class loader.

InvalidStackFrameException - if this stack frame has become invalid. Once the frame's thread is resumed, the stack frame is no longer valid.

VMMismatchException - if a Mirror argument and this mirror do not belong to the same VirtualMachine.