Command

All Known Implementing Classes:

CmdAddShape, CmdBringToBack, CmdBringToFront, CmdRemoveShape, CmdSelectShape, CmdToBack, CmdToFront, CmdUpdateCircle, CmdUpdateHexagon, CmdUpdateLine, CmdUpdatePoint, CmdUpdateRectangle, CmdUpdateSquare
```
public interface Command
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Represent inferface for all commands in the application.
Define two methods:
- execute() - Execute some command.
- unexecute() - Undo some command.

- Method Summary
  
  All Methods Instance Methods Abstract Methods
  Modifier and Type Method Description
  
  void execute()
  
  void unexecute()

- Method Detail
  - execute
```
void execute()
```
  - unexecute
```
void unexecute()
```