Java Programming: Understanding Classes, Variables, and Methods, Slides of Object Oriented Programming

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1

Chapter 5: Defining Classes

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Basics of Classes

• An object is a member of a class type
• What is a class? Fields & Methods
• Types of variables:
  • Instance: each instance (object) of the class will have its own copy of instance variables
  • Class: Only one copy is shared by all objects
• Types of methods: Instance & class (static) method
• Accessing variables and methods (dot operator)
• Accessing static variables and methods?
• Methods: return type, name, & parameters
• Accessing class Data members in methods
• Example: Sphere.java

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Basics of Classes (cont)

• Initialization blocks are used to initialize large

number of variables like the elements of a large

array. Ex. TryInitialization (try non static)

• Constructor: Mainly for guaranteeing that class

variables are properly initialized. Ex. Sphere &

CreateSphere (Compile & run)

• Method overloading and multiple constructors

(CreateShper2 directory)

• Using objects (Point.java, Line.java, &

TryGeometry.java)

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JAVA Packages

• Recursion means a method can call itself!! A behavior that can be very useful. Ex: 234-PowerCalc.java
• A Java package is basically a group of Java classes stored in a directory that has the exact name as the package name
• To create a package use the “package ” as the first statement in all the classes of that package
• To compile a class in a package, the path to that package should be defined in your “classpath” variable or use – classpath compile option
• To run a class in a package, you need to run JVM from the upper directory containing that package and to specify the name of the package & the class name separates by a period.
• Standard Java packages. See documentation

5

Access Attributes & Nested Classes

• There are four attributes: friendly, public,

private, and protected

• Ex: 251-Point, 252-Line, & 254-TryPackage
• Java nested classes & static nested classes.

Ex: MagicHat & TryNesstedClasses

• Using Non-static nested classes. Ex: MagicHat
• The finalize() method
• You can declare native methods using the

“native” keyword but you lose portability.