javaintro.md
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# Introduction to Java Programming
## 1. Basic Program Structure
Every Java program starts with a class, and the main method is the entry point of the program. Here's a simple example:
```java
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}
```
This structure is fundamental to Java:
- `public class`: Declares a class that can be accessed from anywhere
- `static void main(String[] args)`: The main method that runs when you execute the program
- `System.out.println()`: Prints text to the console
## 2. Variables and Data Types
Java is a strongly-typed language, meaning you must declare the type of each variable. Here are the basic data types:
```java
public class Variables {
public static void main(String[] args) {
// Numeric types
int age = 25; // Whole numbers
double price = 19.99; // Decimal numbers
// Text
char grade = 'A'; // Single character
String name = "John Doe"; // Text string
// Boolean
boolean isStudent = true; // true or false
// Printing variables
System.out.println("Name: " + name);
System.out.println("Age: " + age);
System.out.println("Grade: " + grade);
}
}
```
## 3. Control Flow Statements
Control flow statements help you make decisions and repeat actions in your code.
### If-Else Statements
```java
public class ControlFlow {
public static void main(String[] args) {
int score = 85;
if (score >= 90) {
System.out.println("Excellent!");
} else if (score >= 80) {
System.out.println("Good job!");
} else {
System.out.println("Keep practicing!");
}
}
}
```
### Loops
```java
public class Loops {
public static void main(String[] args) {
// For loop
System.out.println("Counting with for loop:");
for (int i = 1; i <= 5; i++) {
System.out.println("Count: " + i);
}
// While loop
System.out.println("\nCounting with while loop:");
int count = 1;
while (count <= 5) {
System.out.println("Count: " + count);
count++;
}
}
}
```
## 4. Arrays
Arrays allow you to store multiple values of the same type:
```java
public class ArrayExample {
public static void main(String[] args) {
// Declaring and initializing an array
int[] numbers = {1, 2, 3, 4, 5};
// Accessing array elements
System.out.println("First number: " + numbers[0]);
// Array iteration
System.out.println("\nAll numbers:");
for (int number : numbers) {
System.out.println(number);
}
// Creating an array of strings
String[] fruits = new String[3];
fruits[0] = "Apple";
fruits[1] = "Banana";
fruits[2] = "Orange";
System.out.println("\nFruits:");
for (String fruit : fruits) {
System.out.println(fruit);
}
}
}
```
## 5. Methods
Methods help you organize code into reusable blocks:
```java
public class Methods {
public static void main(String[] args) {
// Calling methods
greet("Alice");
int sum = add(5, 3);
System.out.println("Sum: " + sum);
}
// Method with no return value (void)
public static void greet(String name) {
System.out.println("Hello, " + name + "!");
}
// Method that returns a value
public static int add(int a, int b) {
return a + b;
}
}
```
These examples cover the fundamental concepts you'll need to start programming in Java. Remember to:
- Save each class in a separate file with the same name as the class
- Compile your code using `javac FileName.java`
- Run your program using `java FileName`
Practice with these examples and modify them to experiment with different values and behaviors. This hands-on experience will help solidify your understanding of Java basics.
Introduction to Java Programming
1. Basic Program Structure
Every Java program starts with a class, and the main method is the entry point of the program. Here's a simple example:
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}
This structure is fundamental to Java:
public class: Declares a class that can be accessed from anywherestatic void main(String[] args): The main method that runs when you execute the programSystem.out.println(): Prints text to the console
2. Variables and Data Types
Java is a strongly-typed language, meaning you must declare the type of each variable. Here are the basic data types:
public class Variables {
public static void main(String[] args) {
// Numeric types
int age = 25; // Whole numbers
double price = 19.99; // Decimal numbers
// Text
char grade = 'A'; // Single character
String name = "John Doe"; // Text string
// Boolean
boolean isStudent = true; // true or false
// Printing variables
System.out.println("Name: " + name);
System.out.println("Age: " + age);
System.out.println("Grade: " + grade);
}
}
3. Control Flow Statements
Control flow statements help you make decisions and repeat actions in your code.
If-Else Statements
public class ControlFlow {
public static void main(String[] args) {
int score = 85;
if (score >= 90) {
System.out.println("Excellent!");
} else if (score >= 80) {
System.out.println("Good job!");
} else {
System.out.println("Keep practicing!");
}
}
}
Loops
public class Loops {
public static void main(String[] args) {
// For loop
System.out.println("Counting with for loop:");
for (int i = 1; i <= 5; i++) {
System.out.println("Count: " + i);
}
// While loop
System.out.println("\nCounting with while loop:");
int count = 1;
while (count <= 5) {
System.out.println("Count: " + count);
count++;
}
}
}
4. Arrays
Arrays allow you to store multiple values of the same type:
public class ArrayExample {
public static void main(String[] args) {
// Declaring and initializing an array
int[] numbers = {1, 2, 3, 4, 5};
// Accessing array elements
System.out.println("First number: " + numbers[0]);
// Array iteration
System.out.println("\nAll numbers:");
for (int number : numbers) {
System.out.println(number);
}
// Creating an array of strings
String[] fruits = new String[3];
fruits[0] = "Apple";
fruits[1] = "Banana";
fruits[2] = "Orange";
System.out.println("\nFruits:");
for (String fruit : fruits) {
System.out.println(fruit);
}
}
}
5. Methods
Methods help you organize code into reusable blocks:
public class Methods {
public static void main(String[] args) {
// Calling methods
greet("Alice");
int sum = add(5, 3);
System.out.println("Sum: " + sum);
}
// Method with no return value (void)
public static void greet(String name) {
System.out.println("Hello, " + name + "!");
}
// Method that returns a value
public static int add(int a, int b) {
return a + b;
}
}
These examples cover the fundamental concepts you'll need to start programming in Java. Remember to:
- Save each class in a separate file with the same name as the class
- Compile your code using
javac FileName.java - Run your program using
java FileName
Practice with these examples and modify them to experiment with different values and behaviors. This hands-on experience will help solidify your understanding of Java basics.