Private vs. Protected in Java

In this post we look at some of the different modifiers in Java.

The Lead Up

Recently, I discovered a course by Princeton University on Coursera that focuses on algorithms. You can check them out here:

• Algorithms, Part I
• Algorithms, Part II

However, when I checked the course requirements I found that it was taught in Java. At the time I found the course(s) about a week ago (at the time of writing) I knew zero Java, and I still know very little. So off I went to SoloLearn.

There’s a section that covers inheritance in OOP, and I had some familiarity with inheritance from working in other OOP languages such as Python and C/C++. However, I started seeing code snippets with various modifiers and no real outlay of definitions. For example:

class BankAccount {
  private double balance=0;
  public void deposit(double x) {
    if(x > 0) {
      balance += x;
    }
  }
}

And then later on I see:

class Animal {
    protected int legs;
    public void eat() {
        System.out.println("Animal eats");
    }
}
class Dog extends Animal {
    Dog() {
        legs = 4;
    }
}
class MyClass {
    public static void main(String[ ] args) {
        Dog d = new Dog();
        d.eat();
    }
}

So then I wanted to know the difference between private and protected.

The Answer

It turns out Java has what are referred to as modifiers. “What’s a modifier?” you ask. “Don’t worry baby birds. I’ll feed ya.”

A Java access modifier specifies which classes can access a given class and its fields, constructors and methods. Access modifiers can be specified separately for a class, its constructors, fields and methods. Java access modifiers are also sometimes referred to in daily speech as Java access specifiers, but the correct name is Java access modifiers. (See Jenkov.com Java Tutorial)

Aside: Java apparently has “access modifiers” (what we’re talking about here) and non-access modifiers (a subject for another time).

As seen in the table above the 4 types of access modifiers are:

• private - Visible to the class only.
• default - Visible to the package. No modifiers are required.
• protected -Visible to the package and all subclasses.
• public - Visible to the world.

tl;dr: The Answer in One Table

To summarize:

Extra References on Java Modifiers

The below references include extended descriptions of Java modifiers as well as code examples.

• GeeksforGeeks
• w3schools