Enums in Java Programming

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Questions and Answers

Which Java data type is used to represent an employee's age?

  • int (correct)
  • boolean
  • double
  • String

What method is used to display the current date in Java?

  • LocalDate.now() (correct)
  • LocalDate.display()
  • LocalDate.current()
  • LocalDate.getCurrentDate()

What method is used to retrieve the numeric representation of the month in a LocalDate object?

  • getMonth()
  • getMonthValue() (correct)
  • getDayOfMonth()
  • getYear()

Which of the following methods can be used to check if a file is writable?

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

Which class is used to represent both date and time in Java?

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

What is the purpose of the DateTimeFormatter class in Java?

<p>To parse date-time objects (A)</p> Signup and view all the answers

When formatting a date as 'Month Day', which pattern would you use with DateTimeFormatter?

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

What is the return type of the delete() method in the File class?

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

Which of the following is false about the boolean data type in employee details?

<p>It can hold decimal values. (C)</p> Signup and view all the answers

Which method will provide the absolute pathname of a file?

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

What class would you import to obtain only the current time in Java?

<p>java.time.LocalTime (D)</p> Signup and view all the answers

To create a new directory in Java, which method would you use?

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

What does the 'T' in the date-time representation signify?

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

In the employee details structure, which data type is used to store the salary?

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

What will the createNewFile() method return if the file already exists?

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

Which method can be used to retrieve the number of bytes in a file?

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

What is the correct syntax to create an enum in Java?

<p>enum Level { LOW, MEDIUM, HIGH } (A)</p> Signup and view all the answers

Which of the following statements about enum values is true?

<p>Enum values are conventionally written in uppercase letters. (D)</p> Signup and view all the answers

How can you access an enum constant in Java?

<p>With a dot notation such as Level.MEDIUM. (D)</p> Signup and view all the answers

In which scenario are enums often utilized in Java?

<p>Within switch statements to check for corresponding values. (B)</p> Signup and view all the answers

What will be printed when the code 'System.out.println(myVar);' is executed with myVar set to Level.MEDIUM?

<p>The output will be 'MEDIUM'. (D)</p> Signup and view all the answers

What is the correct syntax to create a Scanner object?

<p>Scanner myObj = new Scanner(System.in); (D)</p> Signup and view all the answers

Which method is used to read Strings from input?

<p>The nextLine() method (B)</p> Signup and view all the answers

What does the values() method return when called on an enum type?

<p>An array of all enum constants. (B)</p> Signup and view all the answers

Which of the following is NOT a characteristic of enums?

<p>Enums require a defined default value. (A)</p> Signup and view all the answers

Which method is used to read integers from input?

<p>The nextInt() method (B)</p> Signup and view all the answers

What will happen if you enter an incorrect input type when using nextInt()?

<p>The program will give an InputMismatchException error. (A)</p> Signup and view all the answers

What happens if two enum constants share the same name?

<p>Java produces a compile-time error due to duplicate names. (B)</p> Signup and view all the answers

In the Employee Management System, which data type is used for employee salary?

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

In the example provided, how do you read a continuous string input?

<p>By using the nextLine() method (A)</p> Signup and view all the answers

What type of input does the last prompt in the Employee Management System ask for?

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

What will be the output after entering 'John Doe', 30, 55000.75 for name, age, and salary respectively?

<p>Name: John Doe, Age: 30, Salary: 55000.75 (A)</p> Signup and view all the answers

What is returned by the method when a file is successfully created?

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

What must be managed with a try...catch block during file operations?

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

Which class is used to create a new file in the provided Java code?

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

What will happen if the createNewFile() method is called on an existing file?

<p>It returns false (C)</p> Signup and view all the answers

How should file paths be specified on Windows systems?

<p>Using double backslashes (\) (D)</p> Signup and view all the answers

What method from the FileWriter class is used to write text to the file?

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

What is the purpose of e.printStackTrace() within the catch block?

<p>To display the sequence of method calls that led to the error (C)</p> Signup and view all the answers

What will the absolute path print if a file is successfully created?

<p>The full path on the system (B)</p> Signup and view all the answers

What does the method myObj.canRead() return?

<p>True if the file is readable, false otherwise. (B)</p> Signup and view all the answers

Which of the following classes is NOT mentioned for file operations in Java?

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

What is printed when a file does not exist when using the File class?

<p>The file does not exist. (A)</p> Signup and view all the answers

Which method is used to delete a file in Java?

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

What will be the output if a user tries to delete a file that is currently open?

<p>Failed to delete the file. (C)</p> Signup and view all the answers

What type of information does myObj.length() provide?

<p>The size of the file in bytes. (C)</p> Signup and view all the answers

What will be the output if a user attempts to access a file that does not exist using the File class?

<p>The file does not exist. (A)</p> Signup and view all the answers

Which method is used to retrieve the name of the file represented by a File object?

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

What does the method myObj.canWrite() return if a file is writable?

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

What will the delete() method return if a file is successfully deleted?

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

Which of the following classes can be used to write data to files in Java?

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

What does myObj.length() provide when called on a File object?

<p>The size of the file in bytes (C)</p> Signup and view all the answers

Which condition must be met for the exists() method to return true for a File object?

<p>The file must be accessible on the filesystem (C)</p> Signup and view all the answers

What will happen if the delete() method is called on a folder that contains files?

<p>An error message is displayed (D)</p> Signup and view all the answers

Flashcards

Scanner object creation

Creates an object to read input from the console.

Import statement for Scanner

Imports the Scanner class from the Java util package

Reading strings from input

The nextLine() method reads a whole line of text as a string.

Reading integers from input

The nextInt() method reads an integer from input.

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InputMismatchException

An exception that occurs when incorrect data type is entered for an input.

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Input int data type

Stores whole numbers without decimal points (e.g. 10, 0 , -5).

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Input double data type

Stores numbers with decimals (e.g., 3.14, -2.5, 0.0).

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Input boolean data type

Stores true/false values.

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Enum

A special class representing a group of constants (unchangeable variables).

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Enum Creation

Create an enum using the enum keyword, separating constants with commas. Constants are typically in uppercase.

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Enum Access

Access enum constants using a dot (.) notation, e.g., Level.MEDIUM.

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Enum in a Class

An enum can be defined inside a class.

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Enum in Switch

Enums can be used in switch statements to check for different values.

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Enum values() method

Returns an array containing all the constants of the enum defined.

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Enum Purpose

Enums in programming improve code clarity and maintainability. They define named constants.

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Enum Convention

Enum constant names are typically in uppercase.

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Java LocalDate

Represents a date (year, month, day).

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Java LocalTime

Represents a time (hour, minute, second, nanosecond).

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Java LocalDateTime

Represents both a date and a time.

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LocalDate.now()

Retrieves the current date.

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LocalTime.now()

Retrieves the current time.

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LocalDateTime.now()

Retrieves the current date and time.

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DateTimeFormatter

Formats and parses date-time objects.

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Date-Time API Package

Allows working with dates and times in Java.

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LocalDate

A class in Java used to represent a date.

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getMonth()

Gets the month as an enum (e.g., NOVEMBER).

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getMonthValue()

Gets the month as a number (1-12).

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getDayOfMonth()

Gets the day of the month (e.g., 28).

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File (java.io)

A class in Java for working with files and directories.

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createNewFile()

Creates a new file.

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delete()

Deletes an existing file.

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Creating a file

Using Java's File class to create a new file. The method returns true if successful, false if the file already exists.

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IOException

A checked exception type in Java, to handle potential errors that occur during file operations, such as problems with file creation or access.

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File.createNewFile()

A method of the File class. Returns true if the file was successfully created; false if it already exists.

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try...catch block

A block of code in Java that handles potential exceptions (like IOException).

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File object

Represents a file or directory path.

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Absolute path

A complete path to the file, starting with the root directory.

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Error Handling (IOException)

Using a try-catch block to gracefully manage potential errors that can arise during operations like file creation.

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Escaping backslashes

Using double backslashes (\) in file paths in Java to represent a single backslash, especially for paths on Windows systems.

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File information

Methods to get details about a file, such as its name, path, size, and read/write permissions.

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File existence check

Verifies if a file exists before trying to perform operations on it.

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File name retrieval

Obtains the name of a file, excluding the path.

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File path retrieval

Retrieves the complete path of a file from its location in the file system.

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File readability

Determines if a program can read data from a file.

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File deletability

Check if file can be deleted.

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File deletion

Method to remove a file from the file system.

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File size

Retrieves the size of a file in bytes.

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Study Notes

Enums

  • Enums are special classes representing a group of constants (unchangeable variables).
  • Use the enum keyword instead of class or interface.
  • Separate constants with commas.
  • Constants should be in uppercase.

Accessing Enum Constants

  • Access enum constants using a "dot" syntax.
  • Example: Level myVar = Level.MEDIUM;

Enums Inside a Class

  • Enums can be defined within a class.
  • The output of an enum inside a class depends on the code used to access it.

Enums in Switch Statements

  • Enums are commonly used in switch statements to check for corresponding values.
  • Example: switch (myVar)

Looping Through an Enum

  • Use the values() method to loop through enum constants.
  • Example: for (Level myVar : Level.values()) { ... }

Difference Between Enums and Classes

  • Enums can have attributes and methods, like classes.
  • Enum constants are public, static, and final (unchangeable and cannot be overridden).
  • Enums cannot be used to create objects or extend other classes, but can implement interfaces.

Java User Input (Scanner)

  • The Scanner class is used to get user input.
  • To use, create a Scanner object: Scanner myObj = new Scanner(System.in);
  • Use methods like nextLine(), nextInt(), nextDouble(), nextBoolean() to read different data types.

Input Types (Scanner)

  • nextBoolean(): Reads a boolean value.
  • nextByte(): Reads a byte value.
  • nextDouble(): Reads a double value.
  • nextFloat(): Reads a float value.
  • nextInt(): Reads an integer value.
  • nextLine(): Reads a string value.
  • nextLong(): Reads a long value.
  • nextShort(): Reads a short value.

Integer Input from the User

  • The nextInt() method is used to take integer input from the user.

Java Dates and Times

  • Java uses the java.time package for date and time handling.
  • LocalDate: Represents a date (year, month, day).
  • LocalTime: Represents a time (hour, minute, second, nanoseconds).
  • LocalDateTime: Represents both date and time.
  • DateTimeFormatter: Formats date and time objects.

Formatting Date and Time

  • Use DateTimeFormatter.ofPattern() to format dates and times in a specific way.

File Handling

  • Java's java.io package provides classes for file handling (e.g., creating, reading, updating, deleting).
  • The File class represents a file or directory path, allows file and directory interactions.
  • The createNewFile() method attempts to create a new file.
  • The delete() method deletes a file or directory.

Actions on Files

  • Methods like canRead(), canWrite(), exists(), getName(), getAbsolutePath(), length(), list(), mkdir() are used for various file and folder interactions.
  • The FileWriter class writes content to a file.
  • The FileReader class and the Scanner class read content from a file.

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