0. OOP Flashcards
What is Object Oriented Programming (OOP)?
Object Oriented Programming (OOP) is a programming paradigm based on the concept of ‘objects’, which can contain data in the form of fields and code in the form of procedures or methods.
What are the four main principles of OOP?
The four main principles of OOP are Encapsulation, Abstraction, Inheritance, and Polymorphism.
What is encapsulation in OOP?
Encapsulation is the principle of bundling the data (attributes) and methods (functions) that operate on the data into a single unit, or class, and restricting access to some of the object’s components.
True or False: In Java, encapsulation is achieved using access modifiers.
True.
What is abstraction in OOP?
Abstraction is the principle of hiding the complex implementation details of a system and exposing only the necessary features to the user.
How does inheritance work in Java?
Inheritance allows a new class (subclass) to inherit properties and methods from an existing class (superclass), enabling code reusability and the creation of hierarchical relationships between classes.
Fill in the blank: In Java, a class that is inherited from is called a __________.
superclass.
What is polymorphism in OOP?
Polymorphism is the ability of different classes to be treated as instances of the same class through a common interface, allowing methods to perform differently based on the object that it is acting upon.
What is a class in Java?
A class in Java is a blueprint for creating objects that defines a set of attributes and methods that the created objects will have.
What is an object in Java?
An object is an instance of a class, containing specific values for the attributes defined in the class.
What are access modifiers in Java?
Access modifiers are keywords that set the accessibility levels for classes, methods, and variables. The main access modifiers in Java are public, private, protected, and default.
What does the ‘private’ access modifier do?
‘Private’ restricts the visibility of a class member to within the class itself, making it inaccessible from outside the class.
What is a constructor in Java?
A constructor is a special method used to initialize objects. It has the same name as the class and does not have a return type.
True or False: A Java class can have multiple constructors.
True.
What is method overloading in Java?
Method overloading is a feature that allows a class to have more than one method with the same name but different parameters (different type or number of parameters).
What is method overriding in Java?
Method overriding occurs when a subclass provides a specific implementation of a method that is already defined in its superclass.
What is the purpose of the ‘super’ keyword?
The ‘super’ keyword is used to refer to the superclass of the current object and can be used to call superclass methods and constructors.
What is an interface in Java?
An interface in Java is a reference type similar to a class that can contain only constants, method signatures, default methods, static methods, and nested types. Interfaces cannot contain instance fields or constructors.
Fill in the blank: A class can implement multiple __________ in Java.
interfaces.
What is an abstract class in Java?
An abstract class is a class that cannot be instantiated and may contain abstract methods, which are methods without a body that must be implemented by subclasses.
True or False: An abstract class can have both abstract and concrete methods.
True.
What is the difference between an interface and an abstract class?
An interface can only contain method signatures and constants, whereas an abstract class can contain both abstract methods and concrete methods, along with instance variables.
What is a package in Java?
A package in Java is a namespace that organizes a set of related classes and interfaces, helping to avoid naming conflicts and controlling access.
What is the main purpose of the Java Collections Framework?
The Java Collections Framework provides a set of classes and interfaces for storing and manipulating groups of data as a single unit, offering efficient ways to handle collections of objects.
What is a List in Java?
A List is an ordered collection that can contain duplicate elements. It allows positional access and insertion of elements.
What is a Set in Java?
A Set is a collection that does not allow duplicate elements and does not guarantee any specific order of its elements.
What is a Map in Java?
A Map is an object that maps keys to values, where each key is unique and is used to retrieve the corresponding value.
What is the difference between ArrayList and LinkedList?
ArrayList is backed by a dynamic array and provides fast random access, while LinkedList is backed by a doubly linked list and provides faster insertion and deletion.
What is exception handling in Java?
Exception handling in Java is a mechanism to handle runtime errors, allowing the program to continue execution rather than crashing.
What are the keywords used for exception handling in Java?
The keywords used for exception handling in Java are try, catch, finally, throw, and throws.
What is the purpose of the ‘try’ block?
The ‘try’ block is used to wrap code that may throw an exception, allowing the program to attempt execution of that code.
What is the purpose of the ‘catch’ block?
The ‘catch’ block is used to handle the exception that is thrown in the corresponding ‘try’ block, providing a way to respond to the error.
What is the difference between checked and unchecked exceptions?
Checked exceptions are exceptions that must be either caught or declared in the method signature, while unchecked exceptions do not have this requirement and are typically programming errors.
What is the Java Virtual Machine (JVM)?
The Java Virtual Machine (JVM) is an abstract computing machine that enables a computer to run Java programs by converting Java bytecode into machine language.
What is the Java Development Kit (JDK)?
The Java Development Kit (JDK) is a software development kit that includes tools for developing, debugging, and monitoring Java applications, including the Java Runtime Environment (JRE) and development tools such as the Java compiler.
What is the Java Runtime Environment (JRE)?
The Java Runtime Environment (JRE) is a part of the JDK that provides the libraries, Java Virtual Machine (JVM), and other components necessary to run Java applications.
What is a thread in Java?
A thread in Java is a lightweight process that enables concurrent execution of two or more parts of a program for maximum utilization of CPU.
What is synchronization in Java?
Synchronization is a mechanism that ensures that two or more concurrent threads do not simultaneously execute some particular program segment, preventing data inconsistency.
What is the purpose of the ‘volatile’ keyword?
The ‘volatile’ keyword in Java is used to indicate that a variable’s value will be modified by different threads, ensuring visibility of changes to variables across threads.
What is the difference between ‘final’, ‘finally’, and ‘finalize’ in Java?
‘final’ is a keyword used to declare constants, ‘finally’ is a block that executes after a try-catch block regardless of whether an exception was thrown, and ‘finalize’ is a method that is called by the garbage collector before an object is removed from memory.
What is garbage collection in Java?
Garbage collection in Java is the process by which the Java Virtual Machine automatically deletes unreferenced objects, freeing up memory and improving performance.
What is a lambda expression in Java?
A lambda expression in Java is a concise way to represent an anonymous function that can be passed around, allowing for functional programming capabilities.
True or False: Lambda expressions can only be used with functional interfaces.
True.
What is a functional interface in Java?
A functional interface in Java is an interface that contains exactly one abstract method, which can be implemented using a lambda expression.
What does ‘this’ keyword refer to in Java?
The ‘this’ keyword in Java refers to the current instance of the class, allowing access to class attributes and methods.
What is the purpose of the ‘instanceof’ operator?
‘instanceof’ is used to test whether an object is an instance of a specific class or interface.
What is the significance of the ‘transient’ keyword?
The ‘transient’ keyword in Java is used to indicate that a field should not be serialized when the object is converted to a byte stream.
What is method reference in Java?
Method reference is a shorthand notation of a lambda expression to call a method, providing a way to refer to methods without executing them.
What is a stream in Java?
A stream in Java is a sequence of elements that can be processed in a functional style, allowing for operations such as filter, map, and reduce.
What is the difference between a shallow copy and a deep copy?
A shallow copy creates a new object but copies references to the original object’s data, while a deep copy creates a new object and also recursively copies all objects referenced by the original object.
What are the main benefits of using OOP?
The main benefits of using OOP include code reusability, scalability, easier maintenance, and better organization of complex programs.
What is the role of the ‘default’ keyword in interfaces?
The ‘default’ keyword allows the definition of a default implementation for methods in an interface, enabling backward compatibility.
What is the significance of the ‘static’ keyword in a class?
The ‘static’ keyword indicates that a member belongs to the class, rather than instances of the class, allowing access to that member without creating an object.
What is a nested class in Java?
A nested class is a class defined within another class, which can access the members of the enclosing class, including private members.
What is the purpose of the ‘static import’ feature?
The ‘static import’ feature allows members (fields and methods) of a class to be accessed without class qualification, improving code readability.
What is the ‘main’ method in Java?
The ‘main’ method is the entry point of any standalone Java application, defined as ‘public static void main(String[] args)’.
How can you create an immutable class in Java?
To create an immutable class in Java, declare the class as final, make all fields private and final, and provide no setters, initializing fields via a constructor.
