Java Access Modifiers
Note the keyword public and private . These are access modifiers in Java. They are also known as visibility modifiers.
Note: You cannot set the access modifier of getters methods.
Types of Access Modifier
Before you learn about types of access modifiers, make sure you know about Java Packages.
There are four access modifiers keywords in Java and they are:
| Modifier | Description |
| Default | declarations are visible only within the package (package private) |
| Private | declarations are visible within the class only |
| Protected | declarations are visible within the package or all subclasses |
| Public | declarations are visible everywhere |
Default Access Modifier
If we do not explicitly specify any access modifier for classes, methods, variables, etc, then by default the default access modifier is considered. For example,
package defaultPackage; class Logger < void message()< System.out.println("This is a message"); >>Here, the Logger class has the default access modifier. And the class is visible to all the classes that belong to the defaultPackage package. However, if we try to use the Logger class in another class outside of defaultPackage, we will get a compilation error.
Private Access Modifier
When variables and methods are declared private , they cannot be accessed outside of the class. For example,
class Data < // private variable private String name; >public class Main < public static void main(String[] main)< // create an object of Data Data d = new Data(); // access private variable and field from another class d.name = "Programiz"; >>In the above example, we have declared a private variable named name . When we run the program, we will get the following error:
Main.java:18: error: name has private access in Data d.name = "Programiz"; ^The error is generated because we are trying to access the private variable of the Data class from the Main class.
You might be wondering what if we need to access those private variables. In this case, we can use the getters and setters method. For example,
class Data < private String name; // getter method public String getName() < return this.name; >// setter method public void setName(String name) < this.name= name; >> public class Main < public static void main(String[] main)< Data d = new Data(); // access the private variable using the getter and setter d.setName("Programiz"); System.out.println(d.getName()); >>In the above example, we have a private variable named name . In order to access the variable from the outer class, we have used methods: getName() and setName() . These methods are called getter and setter in Java.
Here, we have used the setter method ( setName() ) to assign value to the variable and the getter method ( getName() ) to access the variable.
We have used this keyword inside the setName() to refer to the variable of the class. To learn more on this keyword, visit Java this Keyword.
Note: We cannot declare classes and interfaces private in Java. However, the nested classes can be declared private. To learn more, visit Java Nested and Inner Class.
Protected Access Modifier
When methods and data members are declared protected , we can access them within the same package as well as from subclasses. For example,
class Animal < // protected method protected void display() < System.out.println("I am an animal"); >> class Dog extends Animal < public static void main(String[] args) < // create an object of Dog class Dog dog = new Dog(); // access protected method dog.display(); >>In the above example, we have a protected method named display() inside the Animal class. The Animal class is inherited by the Dog class. To learn more about inheritance, visit Java Inheritance.
We then created an object dog of the Dog class. Using the object we tried to access the protected method of the parent class.
Since protected methods can be accessed from the child classes, we are able to access the method of Animal class from the Dog class.
Note: We cannot declare classes or interfaces protected in Java.
Public Access Modifier
When methods, variables, classes, and so on are declared public , then we can access them from anywhere. The public access modifier has no scope restriction. For example,
// Animal.java file // public class public class Animal < // public variable public int legCount; // public method public void display() < System.out.println("I am an animal."); System.out.println("I have " + legCount + " legs."); >> // Main.java public class Main < public static void main( String[] args ) < // accessing the public class Animal animal = new Animal(); // accessing the public variable animal.legCount = 4; // accessing the public method animal.display(); >>I am an animal. I have 4 legs.
- The public class Animal is accessed from the Main class.
- The public variable legCount is accessed from the Main class.
- The public method display() is accessed from the Main class.
Access Modifiers Summarized in one figure
Access modifiers are mainly used for encapsulation. It can help us to control what part of a program can access the members of a class. So that misuse of data can be prevented. To learn more about encapsulation, visit Java Encapsulation.
Table of Contents
Java Access Modifiers
Java provides four access modifiers to set access levels for classes, variables, methods and constructors i.e. public, private, protected and default. These access level modifiers determine whether other classes can use a particular field or invoke a particular method.
Let’s quickly compare these access modifiers in nutshell.
- public – accessible everywhere
- protected – accessible in the same package and subclasses outside the package
- default – accessible only in the same package
- private – accessible only in the same class
The access specifiers can be ordered based on their strictness as below. The public is the least restrictive, and the private is the most restrictive.
public > protected > package-private (or default) > private
The public members are accessible from everywhere. A public class, method, constructor, or interface could be accessed from any other class in the application. However, if the public class we are trying to access is in a different package, then we must import the class before using it.
public class Data < private String format; public String getFormat() < return this.format; >public void setFormat(String format) < this.format = format; >>In the above example, getFormat() and setFormat() methods are public so they can be accessed from any class.
Please note that the fields in an interface are implicitly public static final and the methods in an interface are, by default, public .
The protected members are accessible by the classes of the same package and the subclasses outside the package.
In Data class, the method displayMessage() is declared protected, so it can be accessed by all the classes present in the same package where HelloWorld.java is present, as well as child classes present in other packages as well.
If we try to access the displayMessage() in another package without extending the Data class, we get the following compilation error:
'displayMessage()' has protected access in 'com.howtodoinjava.core.basic.accessModifiers.package1.Data'
When we inherit the Data class, then we can access the displayMessage() outside the current package.
public class Main extends Data < public static void main(String[] args) < Main main = new Main(); main.displayMessage(); >>The default access modifier means we do not explicitly declare an access modifier for a class, field, method, etc. The default members are accessible only by the classes in the same package.
Let us remove the protected access from the displayMessage() in the Data class. It changes the access to default.
Now when we try to access the displayMessage() in the child class outside the package, we will start getting the compilation error:
'displayMessage()' is not public in 'com.howtodoinjava.core.basic.accessModifiers.package1.Data'. Cannot be accessed from outside package
The private access modifier is the most restrictive access level. The topmost classes and interfaces cannot be private. The private members are accessible within the same class only. The private methods, variables, and constructors can only be accessed within the declared class itself.
We are modifying the previous example again by changing the default access to private access for the displayMessage() method.
Now the method is private so no other class can access it directly.
2. Levels of Access Control
There are two levels of access control.
- Class level access – allows modifiers to be public, or package-private (default).
- Method level access – allows modifiers to be public, private, protected, or package-private (default).
Local variables and formal parameters cannot take access specifiers. Since they are inherently inaccessible to the outside according to scoping rules, they are effectively private.
Both private and protected can be (and frequently are) applied to nested classes and interfaces, just never top-level classes and interfaces.
Access levels affect us in two ways.
- First, when you use classes that come from another source, access levels determine which members of those classes your own classes can use.
- Second, when you write a class, you must decide what access level every member variable and every method in your class should have.
If other programmers use your class, you want to ensure that errors from misuse cannot happen. Access levels can help you do this.
Controlling Access to Members of a Class
Access level modifiers determine whether other classes can use a particular field or invoke a particular method. There are two levels of access control:
- At the top level public , or package-private (no explicit modifier).
- At the member level public , private , protected , or package-private (no explicit modifier).
A class may be declared with the modifier public , in which case that class is visible to all classes everywhere. If a class has no modifier (the default, also known as package-private), it is visible only within its own package (packages are named groups of related classes you will learn about them in a later lesson.)
At the member level, you can also use the public modifier or no modifier (package-private) just as with top-level classes, and with the same meaning. For members, there are two additional access modifiers: private and protected . The private modifier specifies that the member can only be accessed in its own class. The protected modifier specifies that the member can only be accessed within its own package (as with package-private) and, in addition, by a subclass of its class in another package.
The following table shows the access to members permitted by each modifier.
| Modifier | Class | Package | Subclass | World |
|---|---|---|---|---|
| public | Y | Y | Y | Y |
| protected | Y | Y | Y | N |
| no modifier | Y | Y | N | N |
| private | Y | N | N | N |
The first data column indicates whether the class itself has access to the member defined by the access level. As you can see, a class always has access to its own members. The second column indicates whether classes in the same package as the class (regardless of their parentage) have access to the member. The third column indicates whether subclasses of the class declared outside this package have access to the member. The fourth column indicates whether all classes have access to the member.
Access levels affect you in two ways. First, when you use classes that come from another source, such as the classes in the Java platform, access levels determine which members of those classes your own classes can use. Second, when you write a class, you need to decide what access level every member variable and every method in your class should have.
Let’s look at a collection of classes and see how access levels affect visibility. The following figure shows the four classes in this example and how they are related.
Classes and Packages of the Example Used to Illustrate Access Levels
The following table shows where the members of the Alpha class are visible for each of the access modifiers that can be applied to them.
| Modifier | Alpha | Beta | Alphasub | Gamma |
|---|---|---|---|---|
| public | Y | Y | Y | Y |
| protected | Y | Y | Y | N |
| no modifier | Y | Y | N | N |
| private | Y | N | N | N |
If other programmers use your class, you want to ensure that errors from misuse cannot happen. Access levels can help you do this.
- Use the most restrictive access level that makes sense for a particular member. Use private unless you have a good reason not to.
- Avoid public fields except for constants. (Many of the examples in the tutorial use public fields. This may help to illustrate some points concisely, but is not recommended for production code.) Public fields tend to link you to a particular implementation and limit your flexibility in changing your code.