Complete Java Tutorial for Beginners

1. What is Java?

Java is a high-level, class-based, object-oriented programming language used for building web applications, mobile apps, and much more. It was designed to have as few implementation dependencies as possible.

2. Java Syntax

In Java, a program is made up of one or more classes, and a class contains methods. The entry point of every Java program is the main method.

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

In Java, variables are used to store data. Java is a strongly-typed language, meaning each variable must be declared with a specific type.

int number = 10;  // Integer type
String message = "Hello, Java!";  // String type
boolean isJavaFun = true;  // Boolean type
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4. Operators

Operators are used to perform operations on variables and values. Java provides various operators like arithmetic, relational, and logical operators.

int x = 10;
int y = 5;

int sum = x + y;  // Addition
int diff = x - y; // Subtraction
boolean isEqual = (x == y); // Equality check
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5. Control Flow: If-Else Statements

Control flow statements allow you to execute certain code blocks based on conditions.

int age = 20;
if (age >= 18) {
    System.out.println("You are an adult.");
} else {
    System.out.println("You are a minor.");
}
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6. Loops in Java

Loops allow you to execute a block of code multiple times. There are different types of loops like for, while, and do-while.

for (int i = 0; i < 5; i++) {
    System.out.println(i);  // Output: 0, 1, 2, 3, 4
}
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7. Arrays

Arrays are used to store multiple values in a single variable. Each element is accessed using an index.

int[] numbers = {1, 2, 3, 4, 5};
System.out.println(numbers[0]);  // Output: 1
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8. Methods in Java

Methods are used to perform certain tasks and can return values. They help in reusing code and breaking down a program into smaller, manageable parts.

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

int result = addNumbers(5, 10);  // Output: 15
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9. Object-Oriented Programming (OOP) in Java

Java is an object-oriented programming language. This means Java programs are based on objects and classes. OOP concepts include inheritance, encapsulation, polymorphism, and abstraction.

class Car {
    String model;
    int year;
    
    public void displayDetails() {
        System.out.println("Model: " + model + ", Year: " + year);
    }
}

Car myCar = new Car();
myCar.model = "Tesla";
myCar.year = 2022;
myCar.displayDetails();
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10. Java Inheritance

Inheritance is a mechanism in Java where one class can inherit the fields and methods of another class. It allows for code reuse and method overriding.

class Animal {
    public void sound() {
        System.out.println("Animal makes a sound");
    }
}

class Dog extends Animal {
    public void sound() {
        System.out.println("Dog barks");
    }
}

Dog dog = new Dog();
dog.sound();  // Output: Dog barks
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11. Java Abstraction

Abstraction is the concept of hiding the internal details of an object and exposing only the essential parts. It can be achieved using abstract classes and interfaces.

abstract class Animal {
    public abstract void sound();
}

class Cat extends Animal {
    public void sound() {
        System.out.println("Cat meows");
    }
}

Animal animal = new Cat();
animal.sound();  // Output: Cat meows
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12. Java Polymorphism

Polymorphism allows objects to be treated as instances of their parent class, with the ability to call methods from the child class. This is achieved via method overriding and method overloading.

class Shape {
    public void draw() {
        System.out.println("Drawing a shape");
    }
}

class Circle extends Shape {
    @Override
    public void draw() {
        System.out.println("Drawing a circle");
    }
}

Shape shape = new Circle();
shape.draw();  // Output: Drawing a circle
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13. Java Exception Handling

Java provides exception handling to deal with errors that may occur during program execution. The key components are try, catch, and finally.

try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Error: " + e.getMessage());
} finally {
    System.out.println("This will always execute.");
}
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14. Java Collections ChatGPT said: Framework

The Java Collections Framework provides a set of interfaces and classes for working with data structures like lists, sets, and maps.

import java.util.ArrayList;
ArrayList names = new ArrayList<>();
names.add("Alice");
names.add("Bob");
names.add("Charlie");
System.out.println(names); // Output: [Alice, Bob, Charlie]
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15. Java Multithreading

Multithreading in Java allows multiple threads to run concurrently, improving the efficiency of programs.

class MyThread extends Thread { public void run() { System.out.println("Thread is running"); } }
MyThread thread = new MyThread();
thread.start();
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Conclusion

This Java tutorial covered key concepts like syntax, variables, operators, control flow, OOP, inheritance, and more. With this foundation, you can start building your Java applications.