code 128 vb.net n The structural description of its participants n The behavioral description of its execution in Java

Make QR-Code in Java n The structural description of its participants n The behavioral description of its execution

These two characteristics are combined, but they can be separated, because at times it is useful to describe the structure and behavior separately.

FIGURE 3-14

Collaboration diagrams can be enhanced by the inclusion of the dynamic behavior of the message sequences exchanged among objects to accomplish a specific purpose. This is called an interaction, and it helps in understanding the dynamics of the system and its participating objects.

Objects have state or status. The state of an object depends on the current activity or condition. A state diagram illustrates the states of the object and the input and transitions that cause changes in the state. The state diagram shows the sequences of states that an object passes through during its lifetime. They correspond to prompts for input coupled with the responses and actions. A state machine is a diagram of states and transitions that describe the response of an object of a given class to the receipt of external stimuli, and it is generally attached to a class or a method. A state diagram represents a state machine: a state being a condition during the life of an object or an interaction during which it

satisfies some condition, performs some action, or waits for some event. A state may correspond to ongoing activity. Such activity is expressed as a nested state machine. For example, you may reprompt the user to enter missing form items that are required to process a transaction, such as user login. Alternatively, ongoing activity may be represented by a pair of actions one that starts the activity on entry to the state and one that terminates the activity on exit from the state. The example state diagram shown in Figure 3-15 models the login part of an online trading system. Logging in consists of entering a valid user ID and password,

FIGURE 3-15

and then submitting the information for validation against a security database of valid users and their passwords. Logging in can be factored into four nonoverlapping states: checking whether user ID is logged in, getting user ID and password, validating same, and rejecting/accepting the user. From each state comes a complete set of transitions that determine the subsequent state.

An activity diagram is essentially a fancy flowchart. Activity diagrams and state diagrams are related. An activity diagram in a similar manner to the relationship between an object and class diagram is a special case of a state diagram in which all the states are action states and all the transitions are triggered by completion of the actions in the source states. The entire activity diagram is attached to a class or a use case. The purpose of this diagram is to focus on the functionality that flows from internal processing. Activity diagrams are used in situations for which the events represent the completion of internally generated actions that is, procedure flow. State diagrams, on the other hand, are used in situations for which asynchronous events predominate. Figure 3-16 shows the process for making a trade.

Component diagrams are physical versions of class diagrams. A component diagram shows the relationships and dependencies between software components, including Java source code components, Java class components, and Java deployable components JAR (Java Archive) files. Within the deployment diagram, a software component may be represented as a component type. With respect to Java and J2EE, some components exist at compile time (such as makeTrade.java), some exist at archive time (makeTrade.class), and some exist at runtime (Trade.ear); some exist at more than one time. So, you can say that a compile-only component is one that is meaningful only at compile time; the runtime component in this case would be an executable program. You can think of this diagram as a kind of compile, JAR, and deploy description.