Java Inheritance and Visibility Modifiers
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Java Inheritance and Visibility Modifiers

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Questions and Answers

What term is used to refer to the original class from which a new class is derived?

  • Superclass (correct)
  • Interface
  • Child class
  • Derived class

    • Inheritance creates a relationship where a derived class is considered an object of its parent class.

    True

    What keyword is used in Java to establish an inheritance relationship?

    extends

    The _____ modifier means that the member can only be accessed within its own class.

    <p>private</p> Signup and view all the answers

    Match the visibility modifiers with their descriptions:

    <p>Public = Visible everywhere Protected = Accessed within its own package or by subclass Private = Only accessed by its own class</p> Signup and view all the answers

    Which of the following best describes 'overriding'?

    <p>Modifying an inherited method in the child class</p> Signup and view all the answers

    Inheritance helps in achieving better software reuse.

    <p>True</p> Signup and view all the answers

    What does the 'super' keyword do in Java?

    <p>It refers to the parent class and is used to invoke the parent's constructor.</p> Signup and view all the answers

    What does the final modifier do in a method?

    <p>The method cannot be overridden</p> Signup and view all the answers

    Siblings in programming are derived from a common parent class.

    <p>False</p> Signup and view all the answers

    What is inheritance called when it is continuously passed down?

    <p>Transitive</p> Signup and view all the answers

    An abstract method is defined as a method header without a ______.

    <p>method body</p> Signup and view all the answers

    Match the following concepts with their definitions:

    <p>Abstract class = Cannot be instantiated Polymorphism = To have many forms Interface = Collection of abstract methods Overloading = Multiple methods with the same name but different signatures</p> Signup and view all the answers

    Why do we typically override the toString() method?

    <p>To get the object's string representation</p> Signup and view all the answers

    An abstract class can be instantiated.

    <p>False</p> Signup and view all the answers

    What is one common feature that should be established in a class hierarchy?

    <p>As far up as they can be</p> Signup and view all the answers

    What does dynamic binding refer to?

    <p>Decisions cannot be made until runtime</p> Signup and view all the answers

    Polymorphism allows a reference variable to refer only to one specific type of object at any given time.

    <p>False</p> Signup and view all the answers

    What does the compareTo method do?

    <p>It compares two inputs against each other.</p> Signup and view all the answers

    A search pool is essentially a group of ______.

    <p>items</p> Signup and view all the answers

    Match the sorting algorithms with their strategies:

    <p>Selection Sort = Find the smallest element and swap it with the first unsorted element Insertion Sort = Pick any item and insert it into its proper place in a sorted sublist</p> Signup and view all the answers

    What is the purpose of casting in programming?

    <p>It allows an object reference to be treated as a different type</p> Signup and view all the answers

    Sorting is the process of arranging a list of items in random order.

    <p>False</p> Signup and view all the answers

    The Comparable interface is a part of the ______ package.

    <p>java.lang</p> Signup and view all the answers

    Which search method does not require an array to be sorted?

    <p>Linear Search</p> Signup and view all the answers

    An exception is always recoverable in a Java program.

    <p>False</p> Signup and view all the answers

    What does a call stack trace indicate?

    <p>It indicates the line where the exception occurred and the method call trail leading to it.</p> Signup and view all the answers

    Binary search eliminates one of the two subarrays because it knows the array is ______.

    <p>sorted</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Exception = An object that defines an unusual or erroneous situation Error = An unrecoverable situation represented as an object Try-catch statement = Used to handle exceptions in a program Call Stack Trace = Indicates the method call trail that leads to an exception</p> Signup and view all the answers

    What happens if an exception occurs and is not handled by the program?

    <p>The program will terminate and produce an error message.</p> Signup and view all the answers

    In binary search, if the target is smaller than the middle element, it is searched in the right subarray.

    <p>False</p> Signup and view all the answers

    What does linear search rely on to find a target element?

    <p>It sequentially checks each element in the search pool.</p> Signup and view all the answers

    What is the purpose of the try block in a try-catch statement?

    <p>To define a block of code to be tested for errors during execution</p> Signup and view all the answers

    The catch block allows you to handle exceptions that are thrown within the try block.

    <p>True</p> Signup and view all the answers

    What does the getMessage method return?

    <p>A string explaining the reason the exception was thrown</p> Signup and view all the answers

    If an exception is not caught, it continues to propagate until it is caught or handled, or until it is passed out of the ________ method.

    <p>main</p> Signup and view all the answers

    Which class do we extend to define our own exceptions?

    <p>Exception</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Throwable = The parent class of all exceptions and errors Checked Exception = Must be caught or listed in the throws clause Unchecked Exception = Does not require explicit handling Finally Clause = Executed no matter how the try block is exited</p> Signup and view all the answers

    The reserved word 'throw' is used to start exception propagation.

    <p>True</p> Signup and view all the answers

    What happens if no exception is thrown in a try-catch statement?

    <p>Processing continues after the try block.</p> Signup and view all the answers

    Study Notes

    Classes and Inheritance

    • A class is a blueprint for an object and represents the concept of an object.
    • Inheritance is a fundamental object-oriented design technique used to create and organize reusable classes.
    • The superclass (parent class, base class) is extended by the subclass (child class).
    • Inheriting classes inherit variables and methods, creating an is-a relationship.
    • Inheritance benefits include software reuse and reduced space requirements.
    • The extends keyword establishes an inheritance relationship in Java.

    Visibility Modifiers

    • public: Member is visible everywhere.
    • protected: Member can be accessed within its own package and by subclasses in other packages.
    • private: Member can only be accessed by its own class.

    Inheritance Concepts

    • super: Refers to the parent class and is often used to invoke the parent's constructor.
    • Overriding: A child class can replace an inherited method with its own definition.
    • Overloading: Multiple methods with the same name, but different signatures, can exist in the same class.
    • final: Prevents a method from being overridden.

    Relationships and Inheritance

    • Classes with the same parent are siblings. They share inherited traits but do not have an inheritance relationship.
    • Common features should be established as high up as possible in a class hierarchy.
    • Inheritance is transitive, meaning traits are continuously passed down through the hierarchy.
    • The toString() method is often overridden to provide a custom string representation of an object.

    Java Interfaces

    • An interface is a collection of abstract methods and constants.
    • Interfaces declare the methods a class must implement.
    • An abstract method has a header but no implementation.
    • The interface and implements keywords are used to define and implement interfaces.

    Abstract Classes

    • Abstract classes are placeholders in a class hierarchy representing generic concepts.
    • Abstract classes cannot be instantiated.

    Polymorphism

    • Meaning "many forms," polymorphism allows messages to be displayed in different forms.
    • It enables one interface with multiple implementations.
    • Polymorphism can change method invocations from one call to the next, through a polymorphic reference.
    • There are two types: compile-time polymorphism and runtime polymorphism.

    Compile-time vs. Runtime Polymorphism

    • Binding refers to how a method invocation connects to its definition.
    • Compile-time binding decides the specific method implementation during compilation.
    • Dynamic binding (late binding) decides the method invocation at runtime.

    Polymorphism with Interfaces

    • Interface reference variables can refer to any object of a class that implements that interface.

    Casting

    • Casting converts a reference to a more specific type.
    • It's used when you know the actual object type, but the compiler needs explicit information.

    Sorting

    • Sorting arranges items in a specific order.
    • Selection sort repeatedly finds the minimum element and swaps it with the current position.
    • Insertion sort inserts each element into its correct place in a sorted sublist.

    The Comparable Interface

    • The Comparable interface is used to compare objects of the same class.
    • Objects implementing Comparable can be compared for sorting purposes.

    The compareTo Method

    • The compareTo method compares two objects. It returns:
      • A negative value if input1 < input2.
      • 0 if input1 == input2.
      • A positive value if input1 > input2.

    Searching

    • Linear Search examines items sequentially in the search pool.
    • Binary search requires a sorted array. It repeatedly halves the search range, eliminating half of the remaining elements with each step.

    ### Exceptions

    • Exceptions represent problems or unusual situations that occur during program execution.
    • An exception is an object defining an unusual or erroneous situation.
    • An error is a usually unrecoverable situation and shouldn't be caught.

    Exception Handling

    • Scenarios causing exceptions:
      • Attempting to access an array element outside its bounds
      • Attempting to divide by zero
      • Attempting to open a file that doesn't exist
    • If an exception is not handled, the program terminates with an error message.
    • Ignoring an exception results in program termination with a message.

    Exception Handling with try-catch Statements

    • try block: Specifies a block of code to be checked for errors.
    • catch block: Defines code to be executed if an exception occurs in the try block.
    • finally clause: Code that runs regardless of whether an exception was thrown or caught.
    • Each catch clause is a catch handler.
    • Exception variables are used to capture the thrown exception within the catch block.
    • The getMessage() method explains the reason for the exception.

    Exception Propagation

    • Exceptions propagate until they are caught or passed out of the main method, causing program termination.

    Creating Custom Exceptions

    • Create custom exceptions by extending the Exception class.

    Throwable Class

    • The Throwable class is the parent of both Error and Exception classes.
    • It provides the foundation for all descendant classes, including throw for exception propagation.

    Checked vs. Unchecked Exceptions

    • Checked exceptions: Must be either caught or listed in the throws clause of any method that might throw them.
    • Unchecked exceptions: Are a subclass of RuntimeException and are not required to be caught or declared in the throws clause.
    • throw keyword: Explicitly throws an exception, starting exception propagation.

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    Description

    Explore the foundational concepts of classes and inheritance in Java. This quiz covers visibility modifiers and how inheritance enhances software reuse through is-a relationships. Test your understanding of key terms like super, overriding, and overloading.

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