When Abstract methods are used?

Java Programming Language > Fundamentals of Object-Oriented Programming > Object-Oriented Paradigm

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Answer:

If you want a class to contain a particular method but you want the actual implementation of that method to be determined by child classes, you can declare the method in the parent class as abstract.

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100. What is Encapsulation?

Answer:

It is the technique of making the fields in a class private and providing access to the fields via public methods. If a field is declared private, it cannot be accessed by anyone outside the class, thereby hiding the fields within the class. Therefore encapsulation is also referred to as data hiding.

Encapsulation is one of the four fundamental concepts of Object-Oriented Programming (OOP) and is a mechanism that binds together code and data, hiding the implementation details and making them inaccessible to other objects outside the encapsulated object. In Java, encapsulation is achieved through the use of classes and access modifiers (public, private, protected) which control the visibility of class members (methods and variables). This allows data to be protected from outside influences, promotes code reusability, and enhances security by ensuring that data can only be accessed or modified in a controlled manner.

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101. What is the primary benefit of Encapsulation?

Answer:

The main benefit of encapsulation is the ability to modify our implemented code without breaking the code of others who use our code. With this Encapsulation gives maintainability, flexibility and extensibility to our code.

The primary benefit of encapsulation is data hiding and protection. It helps to restrict access to the internal workings of a class and protect the data from accidental or intentional corruption. Encapsulation also promotes the modularity of code and encourages the design of reusable and maintainable software. By encapsulating data and behavior within objects, encapsulation provides the foundation for building robust and secure software systems.

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102. What is an Interface?

Answer:

An interface is a collection of abstract methods. A class implements an interface, thereby inheriting the abstract methods of the interface.

In Java, an interface is a blueprint of a class that contains only abstract methods (methods without a body) and constant fields. An interface is used to define a common behavior for multiple classes, allowing them to work together. Interfaces provide a way to achieve abstraction in Java and are used to define a contract that must be implemented by concrete classes. By implementing an interface, a class agrees to perform the behavior specified in the interface. Interfaces can also be extended by other interfaces, making it possible to define a hierarchy of behaviors.

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103. Give some features of Interface?

Answer:

Interface cannot be instantiated

An interface does not contain any constructors.

All of the methods in an interface are abstract.

In Java, some of the features of an interface include:

Abstract methods: Interfaces can only contain abstract method declarations, and they cannot contain method implementations.
No Constructors: Interfaces cannot contain constructor methods.
100% abstraction: Interfaces are 100% abstract, which means that they only contain abstract methods and constants.
Multiple inheritance: Interfaces allow multiple inheritance, which means that a class can implement more than one interface.
Strong typing: Interfaces enforce strong typing, which means that variables declared as an interface type must only be assigned reference values that implement that interface.
Accessibility: Interface methods are public by default and cannot be declared as private or protected.
Constants: Interfaces can contain constant declarations, which are public, static, and final by default.
Marker interfaces: An interface that does not contain any methods or constants is known as a marker interface, such as Serializable, Cloneable, and Remote.

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104. Define Packages in Java?

Answer: A Package can be defined as a grouping of related types(classes, interfaces, enumerations and annotations ) providing access protection and name space management.

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105. Why Packages are used?

Answer: Packages are used in Java in-order to prevent naming conflicts, to control access, to make searching/locating and usage of classes, interfaces, enumerations and annotations, etc., easier.

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106. What do you mean by Multi-threaded program?

Answer: A multithreaded program contains two or more parts that can run concurrently. Each part of such a program is called a thread, and each thread defines a separate path of execution.

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107. What are the two ways in which Thread can be created?

Answer: Thread can be created by: implementing Runnable interface, extending the Thread class.

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108. What is an applet?

Answer: An applet is a Java program that runs in a Web browser. An applet can be a fully functional Java application because it has the entire Java API at its disposal.

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109. An applet extend which class?

Answer: An applet extends java.applet.Applet class.

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