The University of Akron Summit College

1. The University of AkronSummit College 2440: 160Java Programming Java Fundamentals Instructor: Enoch E. Damson

2. Basic Java Programming Tips • Java is case-sensitive • All Java programs must be stored in a file with a .java extension • Comments are ignored by the compiler • A .java file may contain many classes, but may only have one public class Java Fundamentals

3. Basic Java Programming Tips… • In a .java file with a public class, the class must have the same name as the file • Every Java application program must have a method named main • For every opening brace { or parenthesis (, there must be a corresponding closing brace { or parenthesis ) in Java • Java statements are terminated with semicolons (;), except comments, method headers, or braces Java Fundamentals

4. The Java Application Programmer Interface (API) • A standard library of prewritten classes for performing specific operations such as standard input and output • The classes and their methods are available to all Java programs • Some classes/methods are available automatically in all Java programs • Other classes/methods have to be “imported” into Java programs Java Fundamentals

5. Parts of a Java Application Program • Below is a simple Java application Java Fundamentals

6. Parts of a Java Application Program… • The first line is a non-executable program comment • There are three comments used on Java and they include: • // Line commend • /* Paragraph comment */ • /** Javadoc generated paragraph comment */ Java Fundamentals

7. Parts of a Java Application Program… • The second line defines a class named Hello • Everything used within a Java program must be part of a class • A class can be defined using any name or identifier as long as it satisfies the following criteria: • A class name must begin with a letter of the alphabet (Unicodes etc), an underscore, or a dollar sign • A class name can contain only letters, digits, underscores, or dollar signs • A class name cannot be a Java programming reserved word Java Fundamentals

8. Parts of a Java Application Program… • In Java, standards are employed in the naming of classes to improve readability • This involves using uppercase letters to begin class names, and emphasizing each word put together as a class name with an uppercase letter • E.g., Employee, UnderGradStudent, InventoryItem, Year2000 • It is recommended that established naming conventions be used in order for other programmers to interpret and follow a program • Some valid, but unconventional class names include: • employee, Undergradstudent, Inventory_Item, YEAR2000 • The reserved word public in public class Hello is an access modifier that defines the circumstances under which a class can be accessed • public access is the most liberal type of access that allows other programs to access a class (also used to define methods, and data variables Java Fundamentals

9. Parts of a Java Application Program… • Lines #3 and #8 indicate the beginning and ending scopes of the class • Contents of all classes are enclosed in curly brackets { } which can contain any number of data items and methods Java Fundamentals

10. Parts of a Java Application Program… • Line #4 has the method header, public static void main (String[] args) • public – is the access modifier that allows public access to members of the HelloWorld class • static – is also a modifier that represents uniqueness (a class method) – only one main() method for the HelloWorld class will ever be stored in the computer memory • void – means the main() method returns no value when it is called • main() – all Java applications must have a main() method because that is the first method to be executed by a Java compiler, upon execution of an application • (String[] args) – is the argument passed to the main() method • String[] represents a Java class that can be used to represent a string of characters or array of string objects • args is the identifier used to hold any strings passed to the main() methods Java Fundamentals

11. Parts of a Java Application Program… • Lines #5 and #7 indicate the beginning and ending scopes of the main() method • Contents of all methods are enclosed in curly brackets { } Java Fundamentals

12. Parts of a Java Application Program… • Within the statement in line #6 has the statement: System.out.println(“Hello World”); • System – a class defining the attributes of a collection of similar System objects like out, in. and err • Within, System.out.println(“Hello World”);, • out – is an object that represents the screen and several methods like println( ) are available with the out object • println() – is a method in Java programming that prints a line of output on the screen, and positions the cursor on the next line, and stands ready to accept any additional input • print() also prints a line of output on the screen, but it positions the cursor on the same line as the output, after printing the message • Method names are usually referenced followed by their parenthesis in order to distinguish them from variable names Java Fundamentals

13. Parts of a Java Application Program… • The dots (.) in the statement System.out.println(“Hello World”); are used to separate the names of the class, object, and method • The text “Hello World” is a literal string of characters that is meant to appear exactly as entered • Any literal string in Java programming appears between double quotation marks • The string “Hello World” appears within parenthesis because the string is an argument to a method (in this case the println() method) • Arguments consist of information that a method requires for performing its task Java Fundamentals

14. Special Java Characters Java Fundamentals