Java Programming - Classes and Access Specifiers

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Questions and Answers

What is the scope of the private access specifier in Java?

  • Only for public classes
  • Within a package and its subclasses
  • Throughout the entire package
  • Only within the class (correct)

Which access specifier is used to allow visibility only within a package?

  • Default (correct)
  • Public
  • Private
  • Protected

What concept in Java is used to bind data and methods together?

  • Polymorphism
  • Encapsulation (correct)
  • Inheritance
  • Abstraction

What type of polymorphism is achieved through method overloading?

<p>Compile Time Polymorphism (B)</p> Signup and view all the answers

In Java, which keyword is used to prevent runtime polymorphism?

<p>final (D)</p> Signup and view all the answers

What is the purpose of a helper class in Java?

<p>To contain utility functions for reuse (A)</p> Signup and view all the answers

What does the qualified name of a class include?

<p>Package name and class name (C)</p> Signup and view all the answers

Which of the following is NOT a type of access specifier in Java?

<p>Global (A)</p> Signup and view all the answers

Which access specifier allows visibility within a class and its subclasses only?

<p>Protected (A)</p> Signup and view all the answers

What is the main characteristic of runtime polymorphism?

<p>Class type is determined at runtime (D)</p> Signup and view all the answers

Which keyword is used in Java to define a method that cannot be overridden to prevent runtime polymorphism?

<p>final (B)</p> Signup and view all the answers

Which access specifier can be applied without an explicit keyword?

<p>Default (B)</p> Signup and view all the answers

What does encapsulation in Java primarily achieve?

<p>Hiding of data (C)</p> Signup and view all the answers

Compile time polymorphism is also known by which of the following terms?

<p>Early binding (B), Static binding (C)</p> Signup and view all the answers

What is the primary role of a helper class in Java?

<p>To provide reusable functionalities (D)</p> Signup and view all the answers

Which keyword is used to make a variable or method accessible throughout different packages?

<p>public (B)</p> Signup and view all the answers

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Flashcards

Access Specifiers in Java

A mechanism in Java to control the accessibility of classes, methods, and variables.

Method Overloading

The ability to have multiple methods with the same name but different parameters. This allows the same method name to behave differently based on the type and number of arguments passed.

Compile Time Polymorphism

A type of polymorphism where the method to be executed is determined at compile time based on the method signature.

Runtime Polymorphism

A type of polymorphism where the method to be executed is determined at runtime based on the object type.

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Encapsulation

A technique used to hide data within a class, protecting it from direct access.

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Polymorphism

The ability to execute code differently based on the context. It enables methods to have multiple behaviors.

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Helper Class

A class that assists other classes, often containing utility functions or reusable code.

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Access Specifiers

A way to restrict access to class members (methods, variables) from outside the class.

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Private Access Specifier

A security level that allows access only within the same class. It's the most restrictive level.

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Default Access Specifier

Access is restricted to the same package. It's the default access level if no other specifier is used.

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Protected Access Specifier

Allows access within the same package and also by subclasses outside the package.

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Public Access Specifier

Provides the highest access level. Accessible from anywhere.

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Study Notes

Package Classes

  • To compile package classes, use the command javac -d FileName.java. This saves the compiled class files to the specified directory.
  • To use classes from other packages, use the package keyword with the qualified name (package + class name). Example: a.b.c.d.e.Demo.

Access Specifiers

  • Access specifiers control the visibility of classes or elements within a class.
  • Types of access specifiers:
    • private: Accessible only within the class.
    • default: Accessible within the same package. No keyword needed, it's implicit.
    • protected: Accessible within the package and by subclasses, even if in different packages.
    • public: Accessible throughout the program.

Encapsulation

  • Encapsulation hides data inside a class.
  • Also known as data binding or wrapping of a class.

Interfaces and Abstract Classes

  • Interfaces: Used for multiple inheritance, as blueprints, achieving loosely coupled code, and strong abstraction.
  • Abstract classes: Used for achieving abstraction.

Helper Classes

  • Helper classes provide functions to assist the main program.
  • To avoid redundant code implementation.

Polymorphism

  • Polymorphism allows code execution with different behaviors.
  • Enables code to adapt to requirements.

Types of Polymorphism

  • Compile-time (early/static binding):
    • Achieved through method overloading.
    • Executes methods based on parameters.
    • Useful for end-users
    • Unpreventable
  • Runtime (late/dynamic binding):
    • Achieved through method overriding.
    • Executes methods based on the object type.
    • Useful for developers
    • Preventable using the final keyword.

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