Java Fundamentals: Constants, Char Data Types, and Scanner Input Handling

SLIIT - IT1120: Introduction to Programming

• Institution: Sri Lanka Institute of Information Technology (SLIIT)
• Faculty: Faculty of Computing
• Course Code: IT1120
• Instructional Faculty: Dr. Junius Anjana
• Academic Timing: Year 01 and Semester 01
• Lecture Number: Lecture 3
• Core Topics Covered: Java Constants, Char Data Type, and User Input Handling

Java Constants

• Definition: In the Java programming language, a constant is defined as a specific type of variable that maintains a single, fixed value throughout the entire execution of a program.
• Declaration Keywords:
  • final: Used to ensure the variable value cannot be modified once assigned.
  • static: Often used in conjunction with final to define constants at the class level.

Char Data Type

• General Characteristics:
  • Characters are typically stored using the specialized variable type char.
  • Characters can also be stored within any integer-based data type variable.
  • In Java, characters are versatile and can be treated as either an integer value or a character literal.
• Character Encoding Standards:
  • A significant number of modern computers utilize the ASCII character set, which stands for American Standard Code for Information Interchange.

Relational Operators and Truncation in Decimal Values

• Data Types Involved: This discussion pertains specifically to decimal numbers stored as float or double data types.
• The Concept of Truncation:
  • When computers store these decimal types, they may provide an approximation by rounding off digits that exceed the storage capacity. This phenomenon is formally known as truncation.
• Functional Warning:
  • Due to the inherent truncation errors associated with storing float and double values, these specific types should never be compared using the standard relational operators for equality (==) or inequality (!=).

Java Libraries and Class Frameworks

• Primary Purpose: Java libraries are extensive collections of pre-written code modules designed to add specific functionalities to programs. They serve as essential tools for developers to improve efficiency and reduce the effort required during the software building process.
• Category 1: Standard Libraries (Java Class Libraries):
  • These are included with the Java development environment by default.
  • They provide a significant array of useful methods and classes for fundamental tasks, such as:
    • Reading input provided by the user.
    • Managing and working with various files.
    • Performing complex mathematical calculations.
• Category 2: External Libraries:
  • These are supplemental libraries that provide specialized functionality for niche or specific tasks that are not covered by the standard distribution.
  • Examples include:
    • Graphics processing for video game development.
    • Establishing connections to external databases.
    • Networking tools for working with the internet.
    • User-written libraries created by individual developers or organizations.

Handling Keyboard User Input with the Scanner Class

• Library Location: The standard library responsible for input handling is java.util.
• The Scanner Class: This class is specifically required to capture input entered via the keyboard.
• Implementation Steps:
  • Step 1: Import the Library: You must explicitly inform the program to include the Scanner class using the syntax: import java.util.Scanner;.
  • Step 2: Object Creation: You must instantiate a Scanner object to facilitate communication with the hardware input stream. Syntax: Scanner input = new Scanner(System.in);.
  • Step 3: Capturing Input: Use the appropriate internal function of the Scanner class based on the type of data being entered.
• Methods for String Capture:
  1. String name = input.next();: Captures the next token (usually up to the first space).
  2. String name = input.nextLine();: Captures the entire line of text until a newline character is encountered.

Programming Exercise: Circle Geometry Calculations

• Task Description: Develop a program that accepts the radius of a circle from the keyboard and subsequently displays the circumference and the area.
• Part 1: Pseudocode Strategy:
  • MAIN:
  • DEFINE radius, area, circumference AS FLOAT
  • INPUT radius
  • circumference = 2 * 22.0 / 7 * radius
  • area = 22.0 / 7 * radius * radius
  • PRINT "Area is ", area
  • PRINT "Circumference is ", circumference
  • ENDMAIN
• Part 2: Java Programming Implementation:

import java.util.Scanner;

public class lecture3Exercise {
    public static void main(String[] args) {
        // Declare variables
        double radius, area, circumference;

        // Create an object called input to Scanner class
        Scanner input = new Scanner(System.in);

        // Take radius value as a user input
        System.out.println("Enter radius: ");
        radius = input.nextDouble();

        // Calculations using mathematical formulas
        // Formula for circumference: $2 \times \frac{22.0}{7} \times \text{radius}$
        circumference = 2 * 22.0 / 7 * radius;

        // Formula for area: $\frac{22.0}{7} \times \text{radius}^2$
        area = 22.0 / 7 * radius * radius;

        // Display output results
        System.out.println("Area is " + area);
        System.out.println("Circumference is " + circumference);
    }
}