JAP Hybrid 7

Swing and Threads

• One reason to use threads is to make programs more responsive by delegating time-consuming tasks

Thread Safety and Swing

• Swing is not thread-safe
• Manipulating user interface components from multiple threads can corrupt the user GUI

Rules for Using Swing GUI with Threads

• RULE#1: Complete long actions in a separate worker thread, not in the event dispatch thread.
• The event dispatch thread should avoid input/output operations or calling Thread.sleep() since it may block indefinitely making the application unresponsive.
• RULE#2: Manipulate Swing components only in the event dispatch thread.
• The second rule is known as the "single thread rule" for Swing programming.

Resolving Conflicting Rules

• Use two utility methods to add actions to the event dispatch thread to solve the conflict when updating the UI: invokeLater() and invokeAndWait()
• The label.setText() method cannot be called from your thread; instead call it within invokeLater() and invokeAndWait() methods of the EventQueue class

Examples

• The code affecting the Swing components should be placed into the run() method of a class that implements the Runnable interface
• Pass that class to the static invokeLater() or invokeAndWait() method
• invokeLater() returns immediately after the event is posted to the event queue.
• The run() method is executed asynchronously.
• invokeAndWait() waits until the run() method has been executed, refer to EventQueue class documentation
• Both invokeLater() and invokeAndWait() execute the run() method in the event dispatch thread.
• Using these methods doesn't create a new thread.
• invokeLater() is more appropriate when updating a progress label; users want more progress from the worker thread
• Another way is using new classes (ex: the SwingWorker class from the javax.swing package.

JavaFX & Threads

• JavaFX is also not thread-safe
• The single thread rule applies to JavaFX multithreaded GUI applications
• The runLater() method is available in the Platform class.

Collaboration Diagrams

• A collaboration diagram illustrates the relationships between objects in a system.
• Collaboration diagrams show the architecture of the object residing in the system as it is based on object-oriented programming, as opposed to showing the flow of messages.
• It is also known as a Communication Diagram.

Notations of a Collaboration Diagram

• Objects: Represented by an object symbol with its name and class underlined and separated by a colon
• In the collaboration diagram, objects are utilized in the following ways:
  • The object is represented by specifying their name and class.
  • It is not mandatory for every class to appear.
  • A class may constitute more than one object.
  • In the collaboration diagram, firstly, the object is created, and then its class is specified.
  • To differentiate one object from another object, it is necessary to name them.
• Actors: The actor plays the main role of invoking the interaction, each actor has a respective role and name, and one actor initiates the use case
• Links: An instance of association, which associates the objects and actors portrayed by a solid line representing the relationships between the objects through which messages are sent to navigate to another object
• Messages: Communication between objects carrying information with a sequence number, represented by a labeled arrow placed near a link, and must be navigable in a particular direction

When to Use a Collaboration Diagram

• Essential to depict the relationship between the object
• Collaboration diagrams are best suited for analyzing use cases
• The sequence and collaboration diagrams represent the same information, but portray it differently.

Use Cases for Collaboration Diagrams:

• Model collaboration among objects or roles that carry out use case functionalities and operations.
• Model the mechanism within the architectural design of the system.
• Capture the interactions that represent the flow of messages between objects and roles inside the collaboration.
• Model different scenarios within use cases or operations, involving collaboration of several objects and interactions.
• Support the identification of objects participating in the use case.
• Each message has a sequence number, with top-level messages marked as one and so on and same calls get the same decimal prefix and additional suffixes as per their occurrence.

Steps for Creating a Collaboration Diagram:

• Determine the behavior for realization and implementation.
• Discover structural elements (class roles, objects, subsystems) for performing the functionality of collaboration.
  • Choose the context of an interaction like system, subsystem, use case, or operation.
• Think through alternative situations.
  • Implement a collaboration diagram at an instance level, if needed.
  • Create a specification-level diagram in the instance level sequence diagram to summarize situations.