Java Access Modifiers


Have you ever wanted to define how people would access some of your properties? You would not want anyone using your underwear. However, your close friends and relatives can use your sweater and maybe your car.

Similar to how you set a level of access to your possessions, Java controls access, too. You want to define the access level for variables, methods, and classes, depending on which other classes you want accessing them.

Java provides 4 levels of access modifiers. This means that you can modify access to a variable, method or a class in 4 ways. These 4 ways are private, public, protected and default.

These access modifiers can be applied to fields, methods and classes (Classes are a special case, we will look at them at the end of this artice). Here is a quick overview1 of what the access levels are for each Access Modifier:

Access Modifiers Table Reference

Access modifiersWithin the classWithin the same packageSubclassIn other packages
PublicAccess allowedAccess allowedAccess allowedAccess allowed
ProtectedAccess allowedAccess allowedAccess allowedAccess denied
Default (No access modifier)Access allowedAccess allowedAccess deniedAccess denied
PrivateAccess allowedAccess deniedAccess deniedAccess denied

Private Access Modifier

Allows a variable or method to only be accessed in the class in which it was created. No other class beyond the class that created the variable or method can access it. This is closely similar to your internal organs. They are only accessible to the owner. To make a variable or method private, you simply append the private keyword before the variable or method type, like private int age.

Let us use private in a coding example. If a bank wants to provide an interest rate of 10% on its loans, it would make sure that the interest rate variable would stay private so as no other class would try to access it and change it.
For example:

private double interestRate;

The above example creates a double variable called interestRate and ensures that it is only accessible within the class from which it was created.

An example for a private method is:

private void setAge(){ System.out.println("Set Age"); }

The above example ensures that the method setAge() is accessible only within the class from which it was created and nowhere else.

Public Access Modifier

The public access modifier is the direct opposite of the private access modifier. A class, method or variable can be declared as public which would make it accessible from anywhere. public access modifier can be likened to a public school where anyone can seek admission and be admitted.

To declare a class as public, all you need to do is use the public keyword before the class name:

public class Animal { }

As such, the Animal class can now be accessed by any other class.

Similarly, you use the public keyword for marking variables and methods too, like so:

public int age; public int getAge() { }

The Default Access Modifier

The default access modifier is different from all the other access modifiers in that it has no keyword. To use the default access modifier, you simply use none of the other access modifiers, which means you are using the default access modifier.

For example, to use the default access modifier for a class, you use

class Bird { }

This indicates you are using the default access modifier. It allows a variable, method, or class to be accessible by other classes within the same package. A package is a collection of related classes in a directory. For more information about packages, check out the section on packages.

Any variable, method, or class declared to use the default access modifier cannot be accessed by any other class outside of the package from which it was declared.

Again, similar to classes, you use the default access modifiers for variables and methods like so:

int age; void setNewAge() { }

Don’t forget, the default access modifier does not have a keyword. The absence of the 3 other access modifiers means you are using the default access modifier.

Protected Access Modifier

The protected access modifier is closely related to the default access modifier. The protected access modifier has the properties of the default access modifier but with a little improvement.

Variables and methods are the only ones to use the protected access modifier. The little improvement is that a class outside the package in which the class variable or method was declared can access the said variable or method. This is possible ONLY if it inherits from the original class, however.

A class from another package which has access to the protected variables or methods must have extended the class that created the variables or methods.

Note: without the advantage of inheritance, a default access modifier has the same access as a protected access modifier.

Examples of using the protected access modifier are shown below:

protected int age; protected String getName() { return "My Name is You"; }

Access Modifiers on Classes

By default, classes can only have 2 modifiers:

  • public
  • no modifier (default modifier)

So does this mean classes can never be set to private or protected?

This is logical, why would you want to make a private class? No other class would be able to use it. But sometimes, you can embed a class within another class. These special classes, inner classes, can be set to private or protected so that only its encapsulating class can access it:

public class Car { private String brand; private Engine engine; // outer class ... private class Engine { // inner class ... } }

In the above example, only the Car class can access and use the Engineclass. This can be useful in some cases.

Other classes can never be set to protected or private, because it makes no sense. The protected access modifier is used to make things package-private but with the option to be accessible to subclasses. There is no concept of ‘package-inheritance’ in java.

Sources

1. Oracle docs on Access Modifiers

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