SWE211 Java I/O Quiz

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Questions and Answers

What mode allows both reading and writing when creating a RandomAccessFile object?

  • r+
  • w
  • r
  • rw (correct)

In the RandomAccessFile, which number corresponds to the initial position of the file?

  • 1
  • 9
  • 555
  • 0 (correct)

If the current file length is 800 and new data increases the length to 804, how many bytes were added?

  • 8
  • 4 (correct)
  • 6
  • 2

Which method can be implemented to check if a specific line exists in a file using RandomAccessFile?

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

What is the purpose of the file pointer in a random access file?

<p>To indicate where the next read or write operation occurs. (C)</p> Signup and view all the answers

What happens to the file pointer when data is read from a random access file?

<p>It moves forward to the next data location. (A)</p> Signup and view all the answers

What is the primary purpose of a RandomAccessFile?

<p>To allow random access for reading and writing (A)</p> Signup and view all the answers

How many bytes are referenced by the line representing the eleventh number in the RandomAccessFile?

<p>555 (B)</p> Signup and view all the answers

Which method in RandomAccessFile is used to set the file pointer to a specific position?

<p>seek(long pos) (A)</p> Signup and view all the answers

Which statement about the method writeChars(String s) is true?

<p>It writes a string as a sequence of characters. (D)</p> Signup and view all the answers

Which mode would you use to create a RandomAccessFile for read-only access?

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

What feature is provided by the RandomAccessFile to count the occurrence of a word in a file?

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

How is the length of a random access file obtained?

<p>By calling the length() method. (A)</p> Signup and view all the answers

What does the method getFilePointer() return?

<p>The current offset from the beginning of the file. (C)</p> Signup and view all the answers

Which of the following methods can also be found in DataInputStream and DataOutputStream?

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

When the RandomAccessFile is opened, where is the file pointer initially positioned?

<p>At the beginning of the file. (C)</p> Signup and view all the answers

What is a key characteristic of data stored in binary files?

<p>It is designed for programs to read and process efficiently. (C)</p> Signup and view all the answers

How does a text file represent the decimal integer 199?

<p>As a sequence of characters '1', '9', '9'. (D)</p> Signup and view all the answers

What is the primary advantage of binary files over text files?

<p>They offer more efficient processing. (C)</p> Signup and view all the answers

What encapsulates the properties of a file or a path in Java?

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

Which of the following statements about binary files is correct?

<p>They contain data in a format primarily for machine processing. (C)</p> Signup and view all the answers

What do you need to create in order to perform I/O operations in Java?

<p>Objects from appropriate Java I/O classes. (C)</p> Signup and view all the answers

What does a File object in Java NOT contain?

<p>Methods for reading and writing data (C)</p> Signup and view all the answers

When saving the integer 199 in a binary file, what form does it take?

<p>As a byte-type value C7. (B)</p> Signup and view all the answers

Flashcards

File Pointer

A special marker within a random access file that indicates the current reading or writing position.

Random Access File

A file that allows data to be accessed in any order, regardless of its physical location within the file.

seek(long pos)

A method that moves the file pointer to a specified position within a RandomAccessFile.

getFilePointer()

A method that returns the current position of the file pointer within a RandomAccessFile.

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length()

A method that returns the length, in bytes, of a RandomAccessFile.

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writeChar(int v)

A method that writes a character to a RandomAccessFile as a two-byte Unicode value.

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writeChars(String s)

A method that writes a string to a RandomAccessFile as a sequence of characters.

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RandomAccessFile

A class that allows both reading and writing of data to a file in any order.

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What is a Random Access File?

A file that allows data to be accessed in any order, regardless of its physical location within the file.

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What is the purpose of RandomAccessFile raf = new RandomAccessFile("test.dat", "rw");?

Creates a new RandomAccessFile object, opening the file test.dat for both reading and writing.

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What is the purpose of RandomAccessFile raf = new RandomAccessFile("test.dat", "r");?

Creates a new RandomAccessFile object, opening the file test.dat for read-only access.

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How does the file pointer work in a RandomAccessFile?

The file pointer is positioned within the file, allowing you to access data sequentially by moving the pointer.

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What is the purpose of the seek(long pos) method?

This method moves the file pointer to a specific byte position within a RandomAccessFile.

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What purpose does the getFilePointer() method serve?

A method that returns the current position, in bytes, of the file pointer within a RandomAccessFile.

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What is the purpose of the length() method?

This method returns the length, in bytes, of a RandomAccessFile.

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How does the writeChar(int v) method work?

This method writes a character to a RandomAccessFile as a two-byte Unicode value.

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Scanner Class

A Java class that represents a file's properties and provides methods for reading data from it.

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PrintWriter Class

A Java class that writes data to files, often in a human-readable format.

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Text Files

Files that store data in a format recognizable by humans, using characters to represent information.

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Binary Files

Files that store data in binary format, using a series of bits to represent information. They are not directly readable by humans.

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Input

The process of getting data from a file or other source.

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Output

The process of sending data to a file or other destination.

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Input/Output Stream

A stream of data representing a file that is being read or written.

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File Object

An object that represents an open file, acting as a bridge between the program and the file system.

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Study Notes

Object-Oriented Programming (SWE211) - Java I/O

  • I/O Handling in Java: A File object stores file properties but not I/O methods. To read/write, use Java I/O classes (e.g., Scanner, PrintWriter).

  • Text File vs. Binary File: Text files store data in human-readable form (e.g., "199"). Binary files store data in binary form (e.g., 'C7'). Binary files are more efficient to process. Text files are readable by text editors.

  • Binary I/O Classes: Java provides classes (FileInputStream, DataInputStream, FileOutputStream, DataOutputStream) for efficient binary I/O. The hierarchy includes InputStream, OutputStream, FilterInputStream, FilterOutputStream, and BufferedInputStream, BufferedOutputStream.

  • Input Streams (java.io.InputStream):

    • read(): Reads a byte as an integer (0-255); returns -1 at end of stream.
    • read(byte[] b): Reads up to b.length bytes; returns actual count or -1.
    • read(byte[] b, int off, int len): Reads bytes into b[off] to b[off+len-1]; returns number read or -1 at end.
    • available(): Returns number of bytes readable.
    • close(): Releases resources associated with the stream.
    • skip(long n): Skips n bytes of data(discards).

  • Output Streams (java.io.OutputStream):

    • write(int b): Writes a byte (integer representation).
    • write(byte[] b): Writes the entire byte array.
    • write(byte[] b, int off, int len): Writes b[off] to b[off+len-1].
    • close(): Releases resources.
    • flush(): Writes buffered bytes to the stream.

  • FileInputStream/FileOutputStream: Connects to a file as an input or output stream.

  • FileInputStream Constructors: FileInputStream(String filename), FileInputStream(File file).

  • FileOutputStream Constructors: FileOutputStream(String filename), FileOutputStream(File file), FileOutputStream(String filename, boolean append), FileOutputStream(File file, boolean append).

  • DataInputStream: Reads primitive data types (e.g., integers, characters) from a byte stream

  • DataOutputStream: Writes primitive data types (e.g., integers, characters) to a byte stream

  • ObjectInputStream/ObjectOutputStream: Handle object serialization to files.

  • Serializable Interface: Classes that implement this interface allow Java to serialize object instances.

  • BufferedInputStream, BufferedOutputStream: Use buffers to improve I/O performance.

  • RandomAccessFile: Enables random access read/write operations to files.

  • File Pointer: A marker indicating the current location in a file during read/write operations in RandomAccessFile.

  • RandomAccessFile Methods: seek, getFilePointer, length.

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