unit 5.3

There are 3 types of comments in Java:

1. // Single line comment

2. /* Multiline comment /

3. /** Documentation comment /

The special characters // are used to mark the rest of the line as a comment in many programming languages. If the comment is going to be multiple lines, we use /* to start the comment and */ to end the comment.

There is also a special version of the multi-line comment, /** */, called the documentation comment.

As you write methods in a class, it is a good idea to keep in mind the preconditions and the postconditions for the method and write them in the comments. A precondition is a condition that must be true for your method code to work, for example the assumption that the parameters have values and are not null. The methods could check for these preconditions, but they do not have to. The precondition is what the method expects in order to do its job properly.

A postcondition is a condition that is true after running the method. It is what the method promises to do. Postconditions describe the outcome of running the method, for example what is being returned or the changes to the instance variables. These assumptions are very useful to other programmers who want to use your class and get the correct results.

Determining the preconditions and postconditions help us to test our code and determine the validity of our software. Software validity tests whether the software does what it is supposed to do before it is released. This is sometimes very important. For example, if the code is part of a satellite going to outerspace or is going to be used in an emergency condition, we want to test it thoroughly and make sure it works and is valid before it is put into use.

Preconditions and postconditions can also help us to design better software systems. Software designers often first draw a high-level Use-Case Diagram of a system that shows the different ways that a user might interact with a system before they build it. Here is a simple Use-Case Diagram of a restaurant system. It shows 2 actors in the system: the customer and the staff at the restaurant, and 3 use-cases in circles. A Use-case is a particular user interaction or situation in the system or software, and they often become methods in the program.

The waterfall model, developed in the 1970s, is a step by step model where each phase is finished before the next phase begins. This model has recently been criticized because it is not very adaptable. The more recent Agile development model involves iterative, incremental development where teams works in short 2-3 week sprints to completely develop, test, and release a component of the project to the customer for feedback. It is very adaptable as project requirements change because of early testing, immediate customer feedback and collaboration.

One very popular type of agile development is called Scrum. 

Comments are ignored by the compiler and are not executed when the program is run.

Three types of comments in Java include /* /, which generates a block of comments, //, which generates a comment on one line, and /* */, which are Javadoc comments and are used to create API documentation.

A precondition is a condition that must be true just prior to the execution of a section of program code in order for the method to behave as expected. There is no expectation that the method will check to ensure preconditions are satisfied.

A postcondition is a condition that must always be true after the execution of a section of program code. Postconditions describe the outcome of the execution in terms of what is being returned or the state of an object.

Programmers write method code to satisfy the postconditions when preconditions are met.