Java Basics Classes and objects

In Java, a class is a blueprint or a template for creating objects. An object is an instance of a class, which contains data and methods that operate on that data. Here are some basics of classes and objects in Java:

1. Declaration: To declare a class in Java, you specify the access level, the keyword `class`, the name of the class, and the class body enclosed in curly braces. For example:

public class Person {
    // class members go here
}

This declares a public class called `Person`.

2. Attributes: Attributes, also known as fields or variables, are the data members of a class. They represent the state of an object and define the object’s characteristics. For example:

public class Person {
    String name;
    int age;
}

This declares two attributes for the `Person` class: `name`, which is a string, and `age`, which is an integer.

3. Methods: Methods are the behavior of a class, and they define the actions that an object can perform. Methods are declared inside a class, and they can access the class attributes. For example:

public class Person {
    String name;
    int age;

    public void sayHello() {
        System.out.println("Hello, my name is " + name + " and I am " + age + " years old.");
    }
}

This declares a method called `sayHello` for the `Person` class, which prints a greeting message that includes the person’s name and age.

4. Instantiation: To create an object of a class in Java, you use the `new` keyword followed by the class name and parentheses. For example:

Person john = new Person();

This creates a new object of the `Person` class, which is assigned to the variable `john`.

5. Accessing attributes and methods: You can access the attributes and methods of an object using the dot notation. For example:

john.name = "John";
john.age = 25;
john.sayHello();

This sets the `name` and `age` attributes of the `john` object, and calls the `sayHello` method to print a greeting message.

Classes and objects are the building blocks of Java programming, and they are used to create complex systems and applications. By defining classes and creating objects, you can organize code into reusable and maintainable units, and model real-world entities in your programs.