Classes

In Java, classes are a public entity. They are usually declared in a separate file from the main program.

public class coffee
{
    private String name;
    private double price;
}

Every class we create [even the ready-made ones] inherits the class Object. This is why we can pass an instance of a class as a parameter to a method and why toString and equals methods exist.

Public, static and void

A public entity is visible to the outside world. We can access and modify it.

Whereas a private entity is hidden and forces the users of the class to access it through specified means only. Usually we hide the instance variables of a class.

This is possible thanks to the concept of encapsulation.

Static is a modifier that indicates that the method doesn’t belong to an object [we don’t need an object to access it] and can’t be used to access variables that belong to objects.

We use this modifier if the method is receiving the variables as parameters [case in point - main method].

Constructor

In Java, the constructor has the same name as the class. Its parameters are the instance variables we declared before [if we want, we can change the name in the parameters].

After that, we pass the parameters to our instance variables, which are referred by this.var.

A constructor is automatically created if it’s not defined for a class [however, it will be an empty constructor that does nothing].

public class coffee
{
    private String name;
    private double price;
 
    public coffee(String name, double price)
    {
        this.name = name;
        this.price = 0;
    }
}

We then create objects in our main program using the command new. The arguments passed here will be assigned to the instance variables of the objects [thus, defining its state].

Strings and objects

We use the method toString() to return a string representation of our object.

public class coffee
{
 //program
 public String toString()
 {
  //return statement
 }
}

This, we can call in our main function by the print statement. When we do so, Java parses the statement as below, thanks to abstraction.

```java System.out.println(espresso);

//becomes System.out.println(espresso.toString());