No, we cannot declare a top-level class as private or protected. It can be either public or default (no modifier).
Why protected is not used for class?
class is defined protected —> it cannot be extended from outside package(not visible). And if it cannot be extended then it is meaningless to keep it as protected, because then it will become default access which is allowed.
Can I use protected class in Java?
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.
Can we declare protected method in public class?
Yes, you can declare an abstract method protected. If you do so you can access it from the classes in the same package or from its subclasses.
Can we use protected in subclass Java?
The protected Keyword
While elements declared as private can be accessed only by the class in which they’re declared, the protected keyword allows access from sub-classes and members of the same package.
Can constructor be private?
Yes, we can declare a constructor as private. If we declare a constructor as private we are not able to create an object of a class. We can use this private constructor in the Singleton Design Pattern.
Can a constructor be protected in Java?
Access specifiers/modifiers allowed with constructors
Modifiers public, protected and, private are allowed with constructors. We can use a private constructor in a Java while creating a singleton class. The Singleton’s purpose is to control object creation, limiting the number of objects to only one.
Can we call protected method from outside class Java?
The protected access modifier is accessible within the package. However, it can also accessible outside the package but through inheritance only. We can’t assign protected to outer class and interface. If you make any constructor protected, you cannot create the instance of that class from outside the package.
Can a private method be overridden?
No, we cannot override private or static methods in Java. Private methods in Java are not visible to any other class which limits their scope to the class in which they are declared.
Can we call a protected method in Java?
If a class is not final, you can use an anonymous class to call its protected method: new ClassWithProtectedMethod() { @Override protected void method() { super. method(); } }.
Can abstract method be public?
abstract methods have the same visibility rules as normal methods, except that they cannot be private .
Why protected modifier is used?
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.
Can static methods be private?
Yes, we can have private methods or private static methods in an interface in Java 9.
Can constructor be static?
Java constructor can not be static
One of the important property of java constructor is that it can not be static. We know static keyword belongs to a class rather than the object of a class. A constructor is called when an object of a class is created, so no use of the static constructor.
Can we use void with constructor?
Note that the constructor name must match the class name, and it cannot have a return type (like void ). Also note that the constructor is called when the object is created.
Can abstract methods have constructor?
Like any other classes in Java, abstract classes can have constructors even when they are only called from their concrete subclasses.
Is private method are final?
So, to answer question 2, yes, all compilers will treat private methods as final . The compiler will not allow any private method to be overridden. Likewise, all compilers will prevent subclasses from overriding final methods.
Is protected methods are final?
1) Private methods are final. 2) Protected members are accessible within a package and inherited classes outside the package. 3) Protected methods are final.
Can we overload main method?
Yes, we can overload the main method in Java, but When we execute the class JVM starts execution with public static void main(String[] args) method.
Can we overload final methods?
Can We Override a Final Method? No, the Methods that are declared as final cannot be Overridden or hidden. For this very reason, a method must be declared as final only when we’re sure that it is complete.
Can we have constructor in interface?
No, you cannot have a constructor within an interface in Java. You can have only public, static, final variables and, public, abstract, methods as of Java7.
Can we declare constructor as final?
No, a constructor can’t be made final. A final method cannot be overridden by any subclasses.
Can static method be abstract in Java?
In Java, a static method cannot be abstract. Doing so will cause compilation errors.
Can we declare local inner class as abstract?
Local Inner classes are not a member of any enclosing classes. They belong to the block they are defined within, due to which local inner classes cannot have any access modifiers associated with them. However, they can be marked as final or abstract.
Can we assign superclass object to subclass?
No. It makes zero sense to allow that. The reason is because subclasses generally define additional behavior. If you could assign a superclass object to a subclass reference, you would run into problems at runtime when you try to access class members that don’t actually exist.
Can instance variables be protected?
Protected variables are those data members of a class that can be accessed within the class and the classes derived from that class. In Python, there is no existence of “Public” instance variables. However, we use underscore ‘_’ symbol to determine the access control of a data member in a class.
Can a class be declared with a protected modifier?
Explanation: The protected access modifier is accessible within package and outside the package but only through inheritance. The protected access modifier can be used with data member, method and constructor. It cannot be applied in the class.
What is Polymorphism in Java?
In Java, polymorphism refers to the ability of a class to provide different implementations of a method, depending on the type of object that is passed to the method. To put it simply, polymorphism in Java allows us to perform the same action in many different ways.
Can we create immutable class in Java?
Immutable class in java means that once an object is created, we cannot change its content. In Java, all the wrapper classes (like Integer, Boolean, Byte, Short) and String class is immutable. We can create our own immutable class as well.
Why constructor have no return type?
So the reason the constructor doesn’t return a value is because it’s not called directly by your code, it’s called by the memory allocation and object initialization code in the runtime. Its return value (if it actually has one when compiled down to machine code) is opaque to the user – therefore, you can’t specify it.
Can we use private in interface?
An interface can have private methods since Java 9 version. These methods are visible only inside the class/interface, so it’s recommended to use private methods for confidential code. That’s the reason behind the addition of private methods in interfaces.
Can we overload private method in Java?
Yes, we can overload private methods in Java but, you can access these from the same class.
Can constructor return a value?
No, constructor does not return any value.
Why factory method is static?
The constructors are marked private, so they cannot be called except from inside the class, and the factory method is marked as static so that it can be called without first having an object.
Why constructor is private in Singleton?
In singleton class, we use private constructor so that any target class could not instantiate our class directly by calling constructor, however, the object of our singleton class is provided to the target class by calling a static method in which the logic to provide only one object of singleton class is written/ …
What is a singleton in Java?
In Java, Singleton is a design pattern that ensures that a class can only have one object. To create a singleton class, a class must implement the following properties: Create a private constructor of the class to restrict object creation outside of the class.
What is the role of destructor in class?
Destructors are usually used to deallocate memory and do other cleanup for a class object and its class members when the object is destroyed. A destructor is called for a class object when that object passes out of scope or is explicitly deleted.
What is a static constructor?
A static constructor is used to initialize any static data, or to perform a particular action that needs to be performed only once. It is called automatically before the first instance is created or any static members are referenced.
Can we pass parameter in abstract class?
Even though A is abstract, you can receive parameters of type A (which, in this case, would be objects of type B ). You cannot really pass an object of class A , though, since A is abstract and cannot be instantiated.
Can we create object of interface?
Like abstract classes, interfaces cannot be used to create objects (in the example above, it is not possible to create an “Animal” object in the MyMainClass) Interface methods do not have a body – the body is provided by the “implement” class. On implementation of an interface, you must override all of its methods.
Can return type change in overriding?
From Java 5 onwards, we can override a method by changing its return type only by abiding the condition that return type is a subclass of that of overridden method return type.
Can private methods be overridden?
You cannot override a private or static method in Java. If you create a similar method with same return type and same method arguments in child class then it will hide the super class method; this is known as method hiding. Similarly, you cannot override a private method in sub class because it’s not accessible there.
What is private void in Java?
The private keyword is an access modifier used for attributes, methods and constructors, making them only accessible within the declared class.
Can we declare method as private in Java?
Yes, we can declare the main method as private in Java. It compiles successfully without any errors but at the runtime, it says that the main method is not public.
Can a constructor be protected in Java?
Access specifiers/modifiers allowed with constructors
Modifiers public, protected and, private are allowed with constructors. We can use a private constructor in a Java while creating a singleton class. The Singleton’s purpose is to control object creation, limiting the number of objects to only one.
Can we call protected method from outside class Java?
The protected access modifier is accessible within the package. However, it can also accessible outside the package but through inheritance only. We can’t assign protected to outer class and interface. If you make any constructor protected, you cannot create the instance of that class from outside the package.
How do I access a protected 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.
Can constructors and destructors be inherited?
Constructors and destuctors are not members of the class and not inherited but instead automatically invoked if the sub class has no constructor.
Can we use void with constructor?
Note that the constructor name must match the class name, and it cannot have a return type (like void ). Also note that the constructor is called when the object is created.
Can constructor be static?
Java constructor can not be static
One of the important property of java constructor is that it can not be static. We know static keyword belongs to a class rather than the object of a class. A constructor is called when an object of a class is created, so no use of the static constructor.
Can singleton class have multiple constructors?
EDIT: IF you have a singleton-class you won´t need both constructor. All your initializations can be done by the default one, where you set all important members of that instance whereas the static one can be omitted.
Can static method be overloaded?
As per Java coding convention, static methods should be accessed by class name rather than an object. In short, a static method can be overloaded, but can not be overridden in Java.