Which type of access modifier members are not accessible outside the class?

In object-oriented programming, the concept of 'Encapsulation' is used to make class members public or private i.e. a class can control the visibility of its data members. This is done using access modifiers.

There are three types of access modifiers in TypeScript: public, private and protected.

public

By default, all members of a class in TypeScript are public. All the public members can be accessed anywhere without any restrictions.

Example: public

class Employee {
    public empCode: string;
    empName: string;
}

let emp = new Employee();
emp.empCode = 123;
emp.empName = "Swati";

In the above example, empCode and empName are declared as public. So, they can be accessible outside of the class using an object of the class.

Please notice that there is not any modifier applied before empName, as TypeScript treats properties and methods as public by default if no modifier is applied to them.

private

The private access modifier ensures that class members are visible only to that class and are not accessible outside the containing class.

Example: private

class Employee {
    private empCode: number;
    empName: string;
}

let emp = new Employee();
emp.empCode = 123; // Compiler Error
emp.empName = "Swati";//OK

In the above example, we have marked the member empCode as private. Hence, when we create an object emp and try to access the emp.empCode member, it will give an error.

protected

The protected access modifier is similar to the private access modifier, except that protected members can be accessed using their deriving classes.

Example: protected

class Employee {
    public empName: string;
    protected empCode: number;

    constructor(name: string, code: number){
        this.empName = name;
        this.empCode = code;
    }
}

class SalesEmployee extends Employee{
    private department: string;
    
    constructor(name: string, code: number, department: string) {
        super(name, code);
        this.department = department;
    }
}

let emp = new SalesEmployee("John Smith", 123, "Sales");
emp.empCode; //Compiler Error

In the above example, we have a class Employee with two members, public empName and protected property empCode. We create a subclass

class Employee {
    private empCode: number;
    empName: string;
}

let emp = new Employee();
emp.empCode = 123; // Compiler Error
emp.empName = "Swati";//OK

error TS2445: Property 'empCode' is protected and only accessible within class 'Employee' and its subclasses.

In addition to the access modifiers, TypeScript provides two more keywords: readOnly and static. Learn about them next.

Java provides a number of access modifiers to set access levels for classes, variables, methods, and constructors. The four access levels are −

• Visible to the package, the default. No modifiers are needed.
• Visible to the class only (private).
• Visible to the world (public).
• Visible to the package and all subclasses (protected).

Default Access Modifier - No Keyword

Default access modifier means we do not explicitly declare an access modifier for a class, field, method, etc.

A variable or method declared without any access control modifier is available to any other class in the same package. The fields in an interface are implicitly public static final and the methods in an interface are by default public.

Example

Variables and methods can be declared without any modifiers, as in the following examples −

String version = "1.5.1";

boolean processOrder() {
   return true;
}

Private Access Modifier - Private

Methods, variables, and constructors that are declared private can only be accessed within the declared class itself.

Private access modifier is the most restrictive access level. Class and interfaces cannot be private.

Variables that are declared private can be accessed outside the class, if public getter methods are present in the class.

Using the private modifier is the main way that an object encapsulates itself and hides data from the outside world.

Example

The following class uses private access control −

public class Logger {
   private String format;

   public String getFormat() {
      return this.format;
   }

   public void setFormat(String format) {
      this.format = format;
   }
}

Here, the format variable of the Logger class is private, so there's no way for other classes to retrieve or set its value directly.

So, to make this variable available to the outside world, we defined two public methods: getFormat(), which returns the value of format, and setFormat(String), which sets its value.

Public Access Modifier - Public

A class, method, constructor, interface, etc. declared public can be accessed from any other class. Therefore, fields, methods, blocks declared inside a public class can be accessed from any class belonging to the Java Universe.

However, if the public class we are trying to access is in a different package, then the public class still needs to be imported. Because of class inheritance, all public methods and variables of a class are inherited by its subclasses.

Example

The following function uses public access control −

public static void main(String[] arguments) {
   // ...
}

The main() method of an application has to be public. Otherwise, it could not be called by a Java interpreter (such as java) to run the class.

Protected Access Modifier - Protected

Variables, methods, and constructors, which are declared protected in a superclass can be accessed only by the subclasses in other package or any class within the package of the protected members' class.

The protected access modifier cannot be applied to class and interfaces. Methods, fields can be declared protected, however methods and fields in a interface cannot be declared protected.

Protected access gives the subclass a chance to use the helper method or variable, while preventing a nonrelated class from trying to use it.

Example

The following parent class uses protected access control, to allow its child class override openSpeaker() method −

class AudioPlayer {
   protected boolean openSpeaker(Speaker sp) {
      // implementation details
   }
}

class StreamingAudioPlayer extends AudioPlayer {
   boolean openSpeaker(Speaker sp) {
      // implementation details
   }
}

Here, if we define openSpeaker() method as private, then it would not be accessible from any other class other than AudioPlayer. If we define it as public, then it would become accessible to all the outside world. But our intention is to expose this method to its subclass only, that’s why we have used protected modifier.

Access Control and Inheritance

The following rules for inherited methods are enforced −

• Methods declared public in a superclass also must be public in all subclasses.

• Methods declared protected in a superclass must either be protected or public in subclasses; they cannot be private.

  Which modifiers can not used with outer class?

  Private: The access level of a private modifier is only within the class. It cannot be accessed from outside the class.

  Which access specifier does not allow class members directly outside class?

  In C++, there are three access specifiers: public - members are accessible from outside the class. private - members cannot be accessed (or viewed) from outside the class. protected - members cannot be accessed from outside the class, however, they can be accessed in inherited classes.

  Which modifiers are not allowed in front of class?

  The Java access modifiers private and protected cannot be assigned to a class.

  Which of the following access modifier does not allow a variable to be accessed by classes in the same package?

  Protected Access Modifier - Protected Variables, methods, and constructors, which are declared protected in a superclass can be accessed only by the subclasses in other package or any class within the package of the protected members' class. The protected access modifier cannot be applied to class and interfaces.