Fundamental Programming Structures in Java

 

Fundamental Programming Structures in Java

Java provides a solid foundation for creating reliable and maintainable software through various programming structures. Let’s break down the fundamental elements:

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1. Data Types and Variables

Java is a statically-typed language, which means all variables must be declared before use. The two main categories are:

a. Primitive Data Types

• byte: 8-bit integer (-128 to 127)
• short: 16-bit integer (-32,768 to 32,767)
• int: 32-bit integer (-2^31 to 2^31 - 1)
• long: 64-bit integer (-2^63 to 2^63 - 1)
• float: 32-bit floating-point (Single-precision)
• double: 64-bit floating-point (Double-precision)
• char: 16-bit Unicode character ('\u0000' to '\uffff')
• boolean: True or False (true/false)

b. Reference Data Types

• Objects: Instances of classes.
• Arrays: Objects that store multiple values of a single type.
• Strings: Immutable objects representing sequences of characters.

c. Variable Declaration and Initialization

int age = 25;

double salary = 50000.0;

char grade = 'A';

boolean isJavaFun = true;

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2. Operators

Java supports various operators for manipulating data. These include:

a. Arithmetic Operators

+ (Addition), - (Subtraction), * (Multiplication), / (Division), % (Modulus)

int result = 10 + 5; // Output: 15

b. Relational Operators

==, !=, >, <, >=, <=

boolean isEqual = (10 == 20); // Output: false

c. Logical Operators

&& (AND), || (OR), ! (NOT)

boolean result = (10 > 5) && (20 > 15); // Output: true

d. Assignment Operators

=, +=, -=, *=, /=, %=

int x = 10;

x += 5;  // x becomes 15

e. Increment/Decrement Operators

++, --

int num = 5;

num++;  // num becomes 6

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3. Control Flow Statements

Java provides mechanisms for making decisions and controlling the execution flow.

a. Conditional Statements

1. if Statement

if (age >= 18) {

    System.out.println("You are an adult.");

}

2. if-else Statement

if (age >= 18) {

    System.out.println("You are an adult.");

} else {

    System.out.println("You are a minor.");

}

3. if-else-if Ladder

if (marks >= 90) {

    System.out.println("Grade A");

} else if (marks >= 80) {

    System.out.println("Grade B");

} else {

    System.out.println("Grade C");

}

4. switch Statement

int day = 2;

switch (day) {

    case 1: System.out.println("Monday"); break;

    case 2: System.out.println("Tuesday"); break;

    default: System.out.println("Invalid Day");

}

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b. Looping Statements

1. for Loop

for (int i = 0; i < 5; i++) {

    System.out.println(i);

}

2. while Loop

int i = 0;

while (i < 5) {

    System.out.println(i);

    i++;

}

3. do-while Loop

int i = 0;

do {

    System.out.println(i);

    i++;

} while (i < 5);

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c. Enhanced for Loop (for-each Loop)

Used for iterating over arrays or collections.

int[] numbers = {10, 20, 30, 40};

for (int num : numbers) {

    System.out.println(num);

}

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4. Arrays

Arrays are objects that store multiple values of the same type.

a. Declaration and Initialization

int[] numbers = new int[5];  // Declaration

int[] scores = {90, 80, 70, 60, 50};  // Initialization

b. Accessing Elements

System.out.println(scores[0]);  // Output: 90

c. Multi-dimensional Arrays

int[][] matrix = { {1, 2, 3}, {4, 5, 6} };

System.out.println(matrix[1][2]);  // Output: 6

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5. Methods (Functions)

Methods are reusable blocks of code that perform specific tasks.

a. Declaration and Definition

public static int add(int a, int b) {

    return a + b;

}

b. Calling a Method

int sum = add(5, 10);

System.out.println(sum);  // Output: 15

c. Method Overloading

Creating multiple methods with the same name but different parameters.

public int add(int a, int b) { return a + b; }

public double add(double a, double b) { return a + b; }

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6. Classes and Objects

Java is an object-oriented language, and everything revolves around classes and objects.

a. Creating a Class

public class Student {

    String name;

    int age;

 

    public Student(String name, int age) {

        this.name = name;

        this.age = age;

    }

 

    public void display() {

        System.out.println(name + " is " + age + " years old.");

    }

}

b. Creating an Object

public class Main {

    public static void main(String[] args) {

        Student student = new Student("Krishna", 25);

        student.display();

    }

}

Output:

Krishna is 25 years old.

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7. Input and Output

Java provides several ways to take input and produce output.

a. Standard Output (Printing)

System.out.println("Hello, World!");

b. Standard Input (Using Scanner)

import java.util.Scanner;

 

Scanner scanner = new Scanner(System.in);

System.out.print("Enter your name: ");

String name = scanner.nextLine();

System.out.println("Hello, " + name);

scanner.close();

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8. Packages

Packages are collections of related classes and interfaces that provide modularity.

Creating a Package

package mypackage;

 

public class MyClass {

    public void display() {

        System.out.println("Inside mypackage.");

    }

}

Using a Package

import mypackage.MyClass;

 

public class Main {

    public static void main(String[] args) {

        MyClass obj = new MyClass();

        obj.display();

    }

}

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