- What is protected access java
- Controlling Access to Members of a Class
- What is protected access java
- 1) Private
- Role of Private Constructor
- Note: A class cannot be private or protected except nested class.
- 2) Default
- 3) Protected
- 4) Public
- Java Access Modifiers with Method Overriding
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What is protected access java
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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.
What is protected access java
1) Private
The private access modifier is accessible only within the class.
Simple example of private access modifier
In this example, we have created two classes A and Simple. A class contains private data member and private method. We are accessing these private members from outside the class, so there is a compile-time error.
Role of Private Constructor
If you make any class constructor private, you cannot create the instance of that class from outside the class. For example:
Note: A class cannot be private or protected except nested class.
2) Default
If you don’t use any modifier, it is treated as default by default. The default modifier is accessible only within package. It cannot be accessed from outside the package. It provides more accessibility than private. But, it is more restrictive than protected, and public.
Example of default access modifier
In this example, we have created two packages pack and mypack. We are accessing the A class from outside its package, since A class is not public, so it cannot be accessed from outside the package.
In the above example, the scope of class A and its method msg() is default so it cannot be accessed from outside the package.
3) Protected
The protected access modifier is accessible within package and outside the package but through inheritance only.
The protected access modifier can be applied on the data member, method and constructor. It can’t be applied on the class.
It provides more accessibility than the default modifer.
Example of protected access modifier
In this example, we have created the two packages pack and mypack. The A class of pack package is public, so can be accessed from outside the package. But msg method of this package is declared as protected, so it can be accessed from outside the class only through inheritance.
4) Public
The public access modifier is accessible everywhere. It has the widest scope among all other modifiers.
Example of public access modifier
Java Access Modifiers with Method Overriding
If you are overriding any method, overridden method (i.e. declared in subclass) must not be more restrictive.
The default modifier is more restrictive than protected. That is why, there is a compile-time error.
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Java protected Keyword
The Student subclass accesses a Person class with protected attributes:
class Person < protected String fname = "John"; protected String lname = "Doe"; protected String email = "john@doe.com"; protected int age = 24; > class Student extends Person < private int graduationYear = 2018; public static void main(String[] args) < Student myObj = new Student(); System.out.println("Name: " + myObj.fname + " " + myObj.lname); System.out.println("Email: " + myObj.email); System.out.println("Age: " + myObj.age); System.out.println("Graduation Year: " + myObj.graduationYear); >> Definition and Usage
The protected keyword is an access modifier used for attributes, methods and constructors, making them accessible in the same package and subclasses.
Related Pages
Read more about modifiers in our Java Modifiers Tutorial.
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Java protected Keyword
The Student subclass accesses a Person class with protected attributes:
class Person < protected String fname = "John"; protected String lname = "Doe"; protected String email = "john@doe.com"; protected int age = 24; > class Student extends Person < private int graduationYear = 2018; public static void main(String[] args) < Student myObj = new Student(); System.out.println("Name: " + myObj.fname + " " + myObj.lname); System.out.println("Email: " + myObj.email); System.out.println("Age: " + myObj.age); System.out.println("Graduation Year: " + myObj.graduationYear); >> Definition and Usage
The protected keyword is an access modifier used for attributes, methods and constructors, making them accessible in the same package and subclasses.
Related Pages
Read more about modifiers in our Java Modifiers Tutorial.
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If you want to report an error, or if you want to make a suggestion, do not hesitate to send us an e-mail:
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