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Public

A .java file can have at most one class that is declared public.

  • If present, this class must have the same name as the file.

A .java file can contain additional, non-public classes.

  • This is generally considered a bad practice, however.

Drill

com.example.objs.drills

Create a new class named just A. In A.java, add the following outside the body of class A. 

class B { }
* What happens if you remove public from the definition of class A? * What happens if you add public to the declaration of class B?

Practice Exercise

Later you will learn how to use inner classes: classes defined inside the body of another class.

public

A class, field, or method that is declared public can be seen and used by any other Java class.

Without public, a class can be seen and used only by other classes in the same package.

  • These are the only two options for a class.

Fields, methods, and constructors can be declared with additional visibility modifiers which determine which other classes, if any, can access them.

Modifier Access
public Methods of any class anywhere have access.
protected Methods of subclasses and of any class in the same package have access.
(default) Methods of classes in the same package (directory) have access
private Only methods defined in the same class have access.
  • We will cover visibility in more detail later.

Drill

Objects/com.example.objs.drills.BankApp

Open and examine BankApp, whose run method declares and instantiates two Account objects. Now open Account. Change its two-argument constructor declaration from public to private. What happens when you save?

Change the constructor declaration back to public.

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