Java File Handling and Exceptions Quiz
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Questions and Answers

What does the statement 'File inFile = new File("sample.dat");' accomplish?

  • It checks if the file sample.dat exists in the specified directory.
  • It opens an existing file named sample.dat in the current directory. (correct)
  • It creates a new file named sample.dat.
  • It deletes the file named sample.dat if it exists.

    • Which method is used to check if a File object refers to an actual file on the disk?

  • isDirectory()
  • canRead()
  • exists()
  • isFile() (correct)

    • What is the purpose of the method exists() when called on a File object?

  • To determine whether the file associated with the File object exists. (correct)
  • To rename the file represented by the File object.
  • To open the file for reading or writing.
  • To create a new file if it does not exist.

    • How do you create a File object that specifies a file located in a different directory?

    <p>File inFile = new File(&quot;C:/SamplePrograms/test.dat&quot;); (A)</p> Signup and view all the answers

    What does the isFile() method return if the File object is linked to a directory?

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

    What is the main purpose of exception handling in a program?

    <p>To prevent runtime errors from terminating the program abnormally (C)</p> Signup and view all the answers

    Which of the following describes unchecked exceptions?

    <p>They can occur during runtime without being explicitly handled (A)</p> Signup and view all the answers

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

    <p>To execute code regardless of whether an exception occurred (C)</p> Signup and view all the answers

    What are chained exceptions?

    <p>A process where one exception causes another exception to be thrown (A)</p> Signup and view all the answers

    What class is typically used for writing data to a file in Java?

    <p>PrintWriter (C)</p> Signup and view all the answers

    What is a checked exception?

    <p>An exception that must be either caught or declared in the method signature (D)</p> Signup and view all the answers

    Which statement is true regarding the Scanner class?

    <p>It can be used to read data from various input sources, including files. (B)</p> Signup and view all the answers

    What happens if the method cannot handle an exception?

    <p>The program must either handle the exception or terminate. (B)</p> Signup and view all the answers

    What type of exception is the program specifically handling?

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

    Why is 'input.nextLine()' called in the catch block?

    <p>To clear the scanner buffer for future inputs. (A)</p> Signup and view all the answers

    What is required in the main method to use Scanner in Java?

    <p>Import the java.util.Scanner package. (B)</p> Signup and view all the answers

    Which of the following is NOT a subclass of Throwable?

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

    In the program, what message is displayed if there is an InputMismatchException?

    <p>Try again Incorrect input (B)</p> Signup and view all the answers

    What will the program repeatedly ask for during execution?

    <p>An integer. (C)</p> Signup and view all the answers

    Which exception type indicates problems with class definitions at runtime?

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

    What is the result when a valid integer is entered in the program?

    <p>The number entered is displayed. (B)</p> Signup and view all the answers

    What exception is thrown when a negative radius is provided to the CircleWithCustomException class?

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

    Which method in the CircleWithCustomException class increases the number of objects created?

    <p>CircleWithCustomException(double newRadius) (A)</p> Signup and view all the answers

    What is the purpose of the getRadius() method in the CircleWithCustomException class?

    <p>To return the current radius (B)</p> Signup and view all the answers

    What is the value of the area calculated by the findArea() method when the radius is set to 1.0?

    <p>3.14159 (B)</p> Signup and view all the answers

    Which constructor overloads the default constructor in the CircleWithCustomException class?

    <p>CircleWithCustomException(double newRadius) (C)</p> Signup and view all the answers

    What does the constructor of InvalidRadiusException store as a private field?

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

    How is the number of objects created accessed from the CircleWithCustomException class?

    <p>CircleWithCustomException.getNumberOfObjects() (A)</p> Signup and view all the answers

    In the TestCircleWithCustomException class, what happens when a CircleWithCustomException is instantiated with a radius of -5?

    <p>An InvalidRadiusException is thrown. (D)</p> Signup and view all the answers

    What Java class serves as a wrapper class for filenames and directory paths?

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

    What type of exception is InvalidRadiusException a subclass of?

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

    What is the maximum number of finally blocks that can be associated with a try-catch block?

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

    What happens if an exception is thrown but not caught in a try-catch statement?

    <p>The finally block is executed and then the program stops. (B)</p> Signup and view all the answers

    In which case is the finally block executed?

    <p>After the try block if an exception occurs, regardless of being caught. (C)</p> Signup and view all the answers

    What will occur after the finally block executes?

    <p>The program resumes execution with the next statement. (A)</p> Signup and view all the answers

    Which statement about the finally block is true?

    <p>It always executes regardless of exception handling. (C)</p> Signup and view all the answers

    What does the catch block do in a try-catch-finally structure?

    <p>It executes when an exception matching its type is thrown. (A)</p> Signup and view all the answers

    In case of no exceptions, what order do the blocks execute?

    <p>try -&gt; finally (A)</p> Signup and view all the answers

    If an exception occurs and is caught, which block executes last?

    <p>the finally block (C)</p> Signup and view all the answers

    What is the primary purpose of the finally block?

    <p>To clean up resources regardless of exceptions. (C)</p> Signup and view all the answers

    What is an outcome of using a finally block?

    <p>It ensures critical code runs no matter what. (B)</p> Signup and view all the answers

    Flashcards

    Runtime Error

    An unexpected event that occurs during program execution, causing the program to halt abnormally.

    Exception Handling

    A mechanism to handle runtime errors gracefully, preventing program termination and allowing it to continue running.

    Error Exception

    Exceptions categorized as fatal errors that usually indicate serious problems with the program, requiring termination.

    Exception Exception

    Exceptions categorized as non-fatal errors that can often be handled by the program to continue execution.

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    Try-Catch Block

    A section of code that executes when a specific exception occurs, allowing the program to handle the error and continue running.

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    Declaring Exceptions

    A method's declaration that specifies the types of exceptions it might throw, informing the calling code about potential errors.

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    Exception Propagation

    The process where an unhandled exception travels up the call stack until it's caught by a suitable try-catch block or causes program termination.

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    File Class

    A class in Java (java.io.File) used to represent files and directories in the file system, allowing for operations like checking existence, obtaining properties, and manipulation.

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    inFile.exists()

    The method used to check if a File object represents a file that actually exists on the filesystem.

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    inFile.isFile()

    A method used to determine if a File object represents a file (as opposed to a directory).

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    Creating a File Object

    The process of creating a new File object in Java. This involves providing the file path, which can be a relative path or an absolute path.

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    File Path

    A representation of the location of a file or directory within the file system. Can be absolute (complete path) or relative (partially-specified path based on the current directory).

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    InputMismatchException

    An exception that occurs when the user enters input that does not match the expected data type. For example, if the program expects an integer but the user enters a string, an InputMismatchException will be thrown.

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    RuntimeException

    A class of exceptions that occur during runtime, typically due to issues like incorrect input or invalid data manipulation.

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    ClassNotFoundException

    A class of exceptions that occur when the program attempts to access a non-existent class.

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    IOException

    A class of exceptions that occur during interactions with external resources, such as files, networks, or databases.

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    NullPointerException

    A class of exceptions that occur when an attempt is made to access an object that is null (has no value).

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    IndexOutOfBoundsException

    A class of exceptions that occur when an attempt is made to access an array element outside of its valid range (index).

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    IllegalArgumentException

    A class of exceptions that occur when the program attempts to access an object that is not properly initialized.

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    VirtualMachineError

    A class of errors that occur when the program encounters a situation that prevents it from executing correctly, often due to issues with the Java Virtual Machine (JVM).

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    LinkageError

    A class of errors that occur when there are problems with the program's structure or how it's linked with other parts of the system.

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    finally block

    A code block that will execute regardless of whether an exception is thrown or caught.

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    try block

    A code block that is used to handle unexpected situations during program execution.

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    catch block

    A code block that is used to catch and handle specific exception objects that are thrown within the try block.

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    Matching catch block

    The code block that is associated with a specific exception type. It will be executed if and only if the exception thrown in the try block matches the type specified in the catch block.

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    Uncaught exception

    Indicates that an exception was thrown and not caught in a previous try block. The program then terminates and displays an error message.

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    finalStatements

    The statements that will be executed after either a catch block or directly after the try block, depending on whether an exception was caught or not.

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    Single catch block

    A code block that is used to specify a single exception type to catch. There can be multiple catch blocks for different exception types within a try block.

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    finally block execution order

    A way to ensure that certain parts of the code are executed, regardless of whether an exception occurred or not.

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    Program continues

    The normal path of program execution. It occurs when no exceptions are encountered in the try block.

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    InvalidRadiusException

    A built-in Java exception that is thrown to signal that a method has been called with an invalid radius value. It is used to handle errors related to the radius of a circle.

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    Radius

    The value that determines the size of a circle. A negative radius value is considered invalid in this context.

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    CircleWithCustomException Constructor (with radius)

    This constructor takes a double value representing the radius of the circle. It sets the radius to the given value and initializes the number of objects created. It also includes error handling, throwing an InvalidRadiusException if the radius is negative.

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    CircleWithCustomException Constructor (default)

    This constructor is designed to create a CircleWithCustomException object with a default radius of 1.0. It calls the other constructor with the default radius, effectively setting up a basic circle. It also initializes the count of objects created.

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    setRadius Method

    This method stores the provided newRadius value as the radius of the circle. However, it includes validation to ensure the radius is non-negative. If the newRadius is negative, an InvalidRadiusException is thrown, indicating an invalid radius.

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    getRadius Method

    This method retrieves the current radius stored in the CircleWithCustomException object. This enables access to the circle's size.

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    findArea Method

    This method calculates and returns the area of the circle based on the stored radius. It utilizes the mathematical formula (radius * radius * pi) to compute the area.

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    getNumberOfObjects Method

    This static method provides access to the number of CircleWithCustomException objects created so far. It allows tracking how many circle instances have been created during the execution of the program.

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    CircleWithCustomException Class

    This class defines a CircleWithCustomException type. It's used to create circle objects with custom exception handling for invalid radii. It includes methods for setting and getting the radius, calculating the area, and tracking the number of objects created.

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    Study Notes

    Chapter 12 Exception Handling and Text IO

    • Exception handling is the mechanism for dealing with runtime errors in a program.
    • Runtime errors cause a program to terminate abruptly.
    • Exception handling allows programs to continue running or terminate gracefully.
    • This chapter covers exception handling in Java.

    Motivations

    • Programs terminate abnormally when encountering runtime errors.
    • Exception handling allows programs to keep running, or to terminate in a controlled manner.

    Objectives

    • Understand exceptions and exception handling.
    • Appreciate the advantages of using exception handling.
    • Distinguish between error (fatal) and exception (nonfatal) types, including checked and unchecked exceptions.
    • Declare exceptions in method headers.
    • Throw exceptions within methods.
    • Use try-catch blocks to handle exceptions.
    • Understand how exceptions are propagated.
    • Retrieve information from exception objects.
    • Develop applications with exception handling.
    • Employ the finally clause in try-catch blocks.
    • Use exceptions solely for unexpected errors.
    • Re-throw exceptions in a catch block.
    • Create chained exceptions.
    • Define custom exception classes.
    • Utilize the java.io.File class to handle files and directories.
    • Use the PrintWriter class to write data to files.
    • Use the Scanner class to read data from files.
    • Understand how the Scanner class reads data.
    • Understand the different types of exceptions in Java (e.g., ArithmeticException, NullPointerException, ArrayIndexOutOfBoundsException).

    Exceptions

    • Runtime errors are signaled using exceptions.
    • The statement int y = x/0; will throw an ArithmeticException.
    • The statement System.out.println(x[5]); will throw an ArrayIndexOutOfBoundsException.
    • Accessing a null object will throw a NullPointerException.

    Exception Handling Overview

    • Programs can handle potential runtime exceptions using if statements.
    • A method can be written to handle potential exceptions using an if statement within the method.
    • Using a method to handle specific scenarios allows for cleaner program logic and prevents premature program termination.

    Exception Advantages

    • Exception handling enables a method to throw an exception to its caller.
    • This feature empowers methods to offload exception handling to the calling code.

    Handling InputMismatchException

    • The InputMismatchException is thrown when a method expects input of a certain data type, but receives an input of a different type.
    • It can be handled by enclosing potentially problematic code within a try...catch block.

    Exception Types

    • Hierarchy of exception classes in Java.
    • Runtime exceptions: Errors caught during runtime, often due to programmer logic. Examples: ArithmeticException, NullPointerException, ArrayIndexOutOfBoundsException.
    • Checked exceptions: Exceptions that must be declared or handled by the method that may throw them. Examples: IOException, FileNotFoundException.
    • Errors: Not typically handled by the programmer, indicating serious system errors. Examples: VirtualMachineError, OutOfMemoryError.

    System Errors

    • Error class represents internal system errors that are usually difficult to recover from.

    Exception

    • Exceptions represent errors that occur during program execution.
    • External factors or programming errors can cause exceptions.

    Runtime Exceptions

    • Examples of runtime exceptions: ArithmeticException, NullPointerException, IndexOutOfBoundsException.
    • These exceptions are often ignored by the programmer rather than handled.

    Checked Exceptions vs. Unchecked Exceptions

    • Runtime exceptions are not recoverable by the programmer or code.
    • Checked exceptions need to be handled, thus a try and catch block or throws statement is mandatory.

    Unchecked Exceptions

    • Unchecked exceptions frequently arise from programmer errors (e.g., NullPointerException, ArrayIndexOutOfBoundsException).
    • Unchecked exceptions usually indicate a bug in the program.

    Catching Exceptions

    • A try...catch block is used to handle exceptions
    • Exception-handling blocks include a try block, containing potentially problematic code, and one or more catch blocks, outlining handlers for specific exception types. The optional final block ensures important code runs whether the try block succeeds or not.

    Example: Declaring, Throwing, and Catching Exceptions

    • Code example of declaring, throwing, and catching a custom exception related to invalid radius in a Circle class.

    Throwing Exceptions Example

    • Code demonstrating how to correctly throw exceptions in Java.

    Why Study Exceptions?

    • Handling unchecked exceptions enhances program reliability.
    • Handling checked exceptions is often essential in robust programs.
    • Many Java API methods throw checked exceptions (e.g., file I/O, network connections, database interactions).

    Declaring your own Exceptions

    • Creating custom exception classes enables the programmer to pass data specific to an exception to the exception handler.

    Custom Exception Class Circle Example

    • Creating a custom exception class for handling invalid radius values.

    Text I/O Processing

    • Performing input and output operations on files requires input/output (I/O) classes.
    • The Java File class provides access to file and directory properties.

    The File Class

    • The File class is used to represent files and directories.
    • Methods for checking existence, reading, writing, etc., are provided.

    Some File Methods

    • Methods on the File class such as exists, isFile, isDirectory
    • Methods to retrieve file/directory information, such as getName(), getPath(), getAbsolutePath(), and lastModified().

    Text I/O

    • Details about reading and writing data to/from text files using Scanner and PrintWriter classes.

    Reading Data Using Scanner

    • Methods in the Scanner class for reading data from various sources.

    Class Scanner

    • How to use the Scanner class to read data from files.

    Example: Reading data using Class Scanner

    • A program example that reads data from a file using Scanner.

    Writing Data Using PrintWriter

    • How to use the PrintWriter class to write data to files.

    Writing Data Using PrintWriter

    • Explains creating and using a PrintWriter object to write data to a file.

    Example: Writing data using PrintWriter Example

    • A program example that writes data into a file using PrintWriter.

    Testing before Reading

    • Essential to test for the availability of more data or tokens in a file before attempting to read further data from a file.
    • hasNextDouble and other similar methods can be used to check for the presence of more data in a file before attempting to read further data if possible.

    Rewriting Previous program

    • A revised program to read the entire file, regardless of the number of values it contains.

    Testing Exception Handling

    • The program example uses a try-catch block approach to handling exceptions in the main method, demonstrating exception handling practices.

    Exception Handling - General Form

    • The general structure for handling exceptions.

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