# 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.

Any method on `StackFrame` which takes `StackFrame` as an parameter may throw `VMDisconnectedException` if the target VM is disconnected and the `VMDisconnectEvent` has been or is available to be read from the `EventQueue`.

Any method on `StackFrame` which takes `StackFrame` as an parameter may throw `VMOutOfMemoryException` if the target VM has run out of memory.

Since:
  1.3

## Method Summary

Modifier and Type
Method
Description
`List<Value>`
`getArgumentValues()`
Returns the values of all arguments in this frame.
`Value`
`getValue(LocalVariable variable)`
Gets the `Value` of a `LocalVariable` in this frame.
`Map<LocalVariable, Value>`
`getValues(List<? extends LocalVariable> 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<LocalVariable>`
`visibleVariables()`
Returns a list containing each `LocalVariable` that can be accessed from this frame's location.

### Methods declared in interface Mirror

`toString, virtualMachine`

## Method Details

### location

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 (-1).

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

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

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

List<LocalVariable> 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; the list will be empty if there are no visible variables; specifically, frames in native methods will always return a zero-length list.
Throws:
  `AbsentInformationException` - if there is no local variable 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.
  `NativeMethodException` - if the current method is native.

### visibleVariableByName

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; frames in native methods will always return null.
Throws:
  `AbsentInformationException` - if there is no local variable 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.
  `NativeMethodException` - if the current method is native.

### getValue

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.

### getValues

Map<LocalVariable, Value> getValues(List<? extends LocalVariable> 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.

### setValue

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()`.

In the case of virtual threads, the target VM supports setting values of local variables when this frame is the topmost frame and the thread is suspended at an event. The target VM may support setting local variables in other cases.

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.
  `OpaqueFrameException` - if this frame is on the call stack of a suspended virtual thread, and the target VM does not support setting the value of local variables in this frame.
  `VMCannotBeModifiedException` - if the VirtualMachine is read-only.
See Also:
  - `VirtualMachine.canBeModified()`

### getArgumentValues

List<Value> getArgumentValues()
Returns the values of all arguments in this frame. Values are returned even if no local variable information is present.

Returns:
  a list containing a `Value` object for each argument to this frame, in the order in which the arguments were declared. If the method corresponding to this frame has no arguments, an empty list is returned.
Throws:
  `InvalidStackFrameException` - if this stack frame has become invalid. Once the frame's thread is resumed, the stack frame is no longer valid.
Since:
  1.6