Basic Class: Summary

General

• An OOP class should NEVER assume the programmer is using a specific mode of output. For example, NEVER print to the console (e.g. println()). You have no idea what kinds of programs a programmer will use this class for: console? GUI? phone? Will they want something output to the user or to a file? When an output value is required, have a method return it. When it's an error message, throw an Exception.
• Always JAVADOC you classes properly and according to Javadoc standards.
• Using Javadoc doesn't mean you can omit internal program documentation. Internal program documentation is for other programmers that might end up taking over your project and editing the actual code. Javadoc is for the programmer that ends up buying/downloading/obtaining your finished class(es) and using them in his/her application - that programmer will not be editing your source code to figure out how your class(es) work.
• UML: The following UML notations are often used in textbooks and notes:
  • - (minus sign): private member
  • + (plus sign): public member
  • : (colon): used to separate names with types, for example a parameter might appear as name : String, which means there is a parameter called "name" that is defined as a String parameter. The same is used for method return types, for example toString() : String shows that the method is called toString(), has no parameters, and it returns a String object.
  Example:

  Cat

  - name : String - breed : String - birthDate : LocalDate - hungry : boolean

  + Cat() + Cat(name : String, breed : String, birthDate : LocalDate, hungry : boolean) + getName() : String + setName(name : String) : void + getBreed() : String + setBreed(breed : String) : void + getBirthDate() : LocalDate + setBirthDate(LocalDate date) : void + isHungry() : boolean + setHungry(hungryState : boolean) + meow() : void + feedCat() : void + feedCat(food : Object) : void + toString() : String

Data Members and Fields

• Data members help represent the state of an object.
• Data members should be encapsulated within the class, using the private modifier.
• Fields (constants) should be public and non-static.
• Identifiers should follow the Java naming standards, be descriptive but not too long, and should not use the prefix m_ or any other similar prefix.
• Data members and fields should use the appropriate data type.
• Data members and fields are declared all together at the top or bottom of the class.

Accessor and Mutator Methods

• Accessors:
  • Are always used to provide read-access to a single, private data member.
  • Are always public.
  • Always start with "get" in lower-case, followed by the full data member name properly camel-cased (e.g. for the data member firstName, the proper accessor would get getFirstName()).
  • Don't have any parameters.
  • Always have the same return type as the data member its accessing.
• Mutators:
  • Are always used to provide write-access to a single, private data member (you can omit a mutator on a private data member to create a read-only data member).
  • Are always public.
  • Always start with "set" in lower-case, followed by the full data member name properly camel-cased (e.g. for the data member firstName, the proper mutator would get setFirstName()).
  • Always have a single parameter containing the value to place inside the data member being changed (and must therefore match the data member's data type).
  • Always return void.
  • Usually need to validate the parameter value to make sure it's valid. If the param value is invalid, an IllegalArgumentException is thrown, with an appropriate error message. If the param value is invalid, it is assigned to the data member.

Constructors

• A constructor's job is to construct (create) new instances of the class (new objects) and initialize those objects with valid values.
• Constructors are public.
• Constructors don't have any return type at all, not even void.
• Constructors always have the exact same name as the class, including case.
• Don't put the same code in your constructor(s) as your mutators: just call your mutator methods inside your constructor(s) as appropriate.

The toString() Method

• toString() is part of Java: it comes from the class called Object.
• toString() is always spelled exactly as you see it here, including case (lower-case "to", upper-case "S" on "String").
• toString() is always public and always returns String.
• toString()'s job is to create a formatted "string representation" of a specific object (the object, as a String).