Java Programming Language Cheatsheet

Java, a versatile and powerful programming language, has been a cornerstone of software development for decades. Whether you’re a seasoned developer or just starting your programming journey, having a cheatsheet can be invaluable. This cheatsheet aims to provide a quick reference guide for Java, covering key concepts, syntax, and best practices.

1. Basic Syntax:

Hello, World! Program:

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

Variables and Data Types:

int age = 25;               // Integer
double price = 19.99;       // Double
char grade = 'A';           // Character
boolean isJavaFun = true;   // Boolean
String message = "Hello";   // String

2. Control Flow:

If-Else Statement:

int x = 10;
if (x > 5) {
    System.out.println("x is greater than 5");
} else {
    System.out.println("x is not greater than 5");
}

Switch Statement:

int day = 3;
switch (day) {
    case 1:
        System.out.println("Monday");
        break;
    case 2:
        System.out.println("Tuesday");
        break;
    // ... other cases ...
    default:
        System.out.println("Invalid day");
}

Loops:

for (int i = 0; i < 5; i++) {
    System.out.println("Iteration " + i);
}

while (condition) {
    // Code to be executed while the condition is true
}

do {
    // Code to be executed at least once, then the condition is checked
} while (condition);

3. Functions:

Method Declaration:

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

Calling a Method:

int result = add(3, 4);
System.out.println("Sum: " + result);

Return Statement:

public int multiply(int a, int b) {
    return a * b;
}

4. Object-Oriented Concepts:

Class Declaration:

public class Car {
    String model;
    int year;

    public Car(String model, int year) {
        this.model = model;
        this.year = year;
    }
}

Creating Objects:

Car myCar = new Car("Toyota", 2022);

Inheritance:

public class SportsCar extends Car {
    boolean isConvertible;

    public SportsCar(String model, int year, boolean isConvertible) {
        super(model, year);
        this.isConvertible = isConvertible;
    }
}

5. Exception Handling:

Try-Catch Block:

try {
    // Code that may throw an exception
} catch (ExceptionType e) {
    // Code to handle the exception
} finally {
    // Code that will be executed regardless of whether an exception occurred
}

6. Collections:

ArrayList:

import java.util.ArrayList;

ArrayList<String> fruits = new ArrayList<>();
fruits.add("Apple");
fruits.add("Banana");

HashMap:

import java.util.HashMap;

HashMap<String, Integer> ages = new HashMap<>();
ages.put("Alice", 25);
ages.put("Bob", 30);

7. File Handling:

Reading from a File:

import java.io.BufferedReader;
import java.io.FileReader;
try (BufferedReader br = new BufferedReader(new FileReader("filename.txt"))) {
    String line;
    while ((line = br.readLine()) != null) {
        System.out.println(line);
    }
} catch (IOException e) {
    e.printStackTrace();
}

Writing to a File:

import java.io.BufferedWriter;
import java.io.FileWriter;
try (BufferedWriter bw = new BufferedWriter(new FileWriter("filename.txt"))) {
    bw.write("Hello, World!");
} catch (IOException e) {
    e.printStackTrace();
}

8. Best Practices:

• Follow naming conventions (e.g., camelCase for variables and methods, PascalCase for classes).
• Use meaningful names for variables and functions.
• Comment your code to explain complex logic or functionality.
• Avoid hardcoding values; use constants or configuration files.
• Keep methods short and focused on a single task.

Remember to include necessary import statements, and this cheatsheet covers only the basics. Java is a versatile language, and you can explore more advanced features and best practices as you continue learning. Refer to official documentation.