Java Programming Classes: Creating Objects

Introduction to Java Programming

• Java is a platform-independent programming language, meaning it can run on virtually any operating system without customization.
• Java programs consist of a combination of different classes that cooperate together through the invocation of methods.
• A Java program can be conceived as a network of interrelated objects.

Programming, Compiling, and Executing a Java Program

• Programming involves producing program code (source code).
• Compiling involves automatic translation of the program code into a form that can be executed by a computer.
• Executing a program involves starting and running the generated and compiled program code.

Basic Elements of a Class in Java

• A class in Java has a unique name and can contain attributes and methods.
• The program code of a class is saved in a text file with the file ending *.java.
• Four basic elements are required to create a class:
  • Visibility modifier (defines the visibility of the class for other classes)
  • Class keyword (indicates to the Java compiler that a Java class is programmed)
  • Class name (defines the name for the class and is used as a file name)
  • Curly braces (mark the contents of a class)

Attributes in Java

• An attribute in Java is described with the following elements at a minimum:
  • Visibility modifier
  • Data type
  • Attribute name
• Default values can be assigned to attributes during programming.
• The principle of data encapsulation states that an object can never directly access attributes of another object.

Methods in Java

• A method is a dynamic element of a class that can create, calculate, modify, and delete the values of attributes.
• Methods can be used to read the values of attributes and make them available to other classes.
• The basic elements of a method include:
  • Visibility modifier
  • Signature (uniquely identifies a method and consists of the name of the method and the parameter list)
  • Return data type
  • Method name
  • Parameter list
  • Method body

Main Method: Starting Point of a Java Program

• The main method is the starting point of a Java program.
• The main method is declared as a public static method with a return type of void.
• The main method is used to generate all the objects that are required by the program.
• The main method can be implemented in any class, but there should only be one class with a main method.

Java Runtime Environment (JRE)

• The JRE is required to run a Java program.

• The JRE consists of the Java virtual machine (JVM) and the Java class library.

• The JVM interprets the bytecode and runs it on the operating system being used.

• The Java class library provides functions that are already part of the Java programming language.### Methods in Classes

• Method signatures are identical if they have the same name and parameter list, but the return type can be different.

• A class can have multiple methods with the same name, as long as the parameter lists are different.

• Method names should be chosen to clearly indicate what the method does.

Getter and Setter Methods

• Getter methods return the value of an attribute.
• Setter methods change the value of an attribute to the value passed as a parameter.
• Getter and setter methods are used to access and modify attributes of a class.
• Example: Customer class with getter and setter methods for its attributes.

Implementation of Getter and Setter Methods

• The basic structure of getter and setter methods is the same, with only the names of the methods and parameters changing.
• The this keyword can be used to refer to the object itself and its class attributes, to differentiate between the parameter and the class attribute.

Method Invocation

• Methods can be invoked from within other method bodies of the same class or from method bodies of another class.
• Methods are invoked using their name.
• Example: invoking the getLastname() method to store the value of lastname in a local variable.

Method Overloading

• Method overloading allows multiple methods with the same name but different parameter lists to be implemented in a class.
• This allows developers to define various method behaviors based on the given parameters.
• Example: methods with the same name getLastname() but different parameter lists in the Customer class.