UNIT 1 – Introduction to Java Programming, Data Types, and Control Statements Notes

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Bangalore, Tech Education Desk: Java has long been celebrated as one of the most versatile and powerful programming languages in the world. From mobile apps to enterprise-level systems, Java continues to dominate the technology landscape. Unit 1 of Java programming introduces learners to the fundamentals—its core features, platform components, program structure, data types, operators, and control flow mechanisms. This foundation ensures that students not only understand how to code in Java but also how to think like programmers.

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Java: A Language for All Platforms

Features That Define Java

Java’s popularity stems from its unique combination of simplicity, power, and portability. It is object-oriented, meaning everything revolves around objects and classes, which makes code easier to manage and reuse. Its platform independence, captured by the phrase “Write Once, Run Anywhere,” allows programs compiled in Java to run on any system with a Java Virtual Machine (JVM). Other features such as security, automatic memory management (garbage collection), and support for multithreading make it a go-to language for modern applications.

The Java Ecosystem: JDK, JRE, JVM

To run Java programs, three essential components work together:

  • Java Development Kit (JDK): A full toolkit for developers, containing the compiler (javac), libraries, and tools needed for development.

  • Java Runtime Environment (JRE): Provides the libraries and JVM required to run applications but not to develop them.

  • Java Virtual Machine (JVM): The heart of Java’s platform independence. It converts Java bytecode into machine-specific instructions, ensuring programs can run on multiple devices without modification.

Together, these components form the backbone of Java development and execution.

Anatomy of a Java Program

Every Java program, whether large or small, follows a consistent structure. A typical program starts with a class definition and a main() method, which serves as the entry point.

class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}

This simple program highlights key elements: class declaration, the main() method, and output using System.out.println. The syntax may feel strict at first, but its consistency ensures clarity and reduces errors.

Data Types, Variables, and Operators

Data Types in Java

Java is a statically typed language, meaning every variable must have a declared data type. These types fall into two main categories:

  • Primitive types: Such as int, float, double, char, boolean, which store simple values.

  • Non-primitive types: Such as arrays, strings, and objects, which reference complex structures.

This distinction allows Java to handle both basic operations and complex programming needs.

Variables and Scope

Variables act as containers for storing values. In Java, they must be declared with a type before use, for example:

int age = 20;

Java also enforces rules of scope, meaning variables exist only within the block of code they are declared in.

Operators in Action

Operators allow manipulation of data. Java supports:

  • Arithmetic operators: (+, -, *, /, %)

  • Relational operators: (>, <, ==, !=)

  • Logical operators: (&&, ||, !)

  • Assignment operators: (=, +=, -=)

These operators, combined with variables, form the building blocks of logical problem-solving.

Input and Output Operations

While output in Java is handled through the System.out class (e.g., System.out.println()), input requires the Scanner class from the java.util package.

Example:

import java.util.Scanner;
class InputExample {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.print("Enter your name: ");
String name = sc.nextLine();
System.out.println("Hello, " + name);
}
}

This ability to interact with users makes Java programs dynamic and user-friendly.

Control Statements: Directing the Flow

A program is rarely linear—it often makes decisions or repeats tasks. Java’s control statements enable this flexibility.

Decision-Making Statements

  • if statement: Executes a block if a condition is true.

  • if-else statement: Provides an alternative path if the condition is false.

  • switch statement: Handles multiple conditions more efficiently than nested if-else.

Looping Statements

Repetition is managed using loops:

  • for loop: Ideal for running a block a fixed number of times.

  • while loop: Repeats as long as a condition is true.

  • do-while loop: Executes at least once before checking the condition.

Jump Statements

Sometimes, programs need to break or skip iterations. Java provides:

  • break: Exits from a loop or switch statement.

  • continue: Skips the current iteration and moves to the next.

  • return: Exits from a method, optionally returning a value.

These statements give programmers fine-grained control over the flow of execution.

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