Computer Knowledge

Java Core Classes and Threads

1,473 Questions

Java core classes and threads form the foundation of object oriented programming and are crucial for IT officer and programming exams. This includes concepts like string mutability, collections, and multithreading. Solve these questions to test your practical coding and theoretical knowledge.

String and StringBuffer classesThread execution methodsJava collections frameworkCharacter streams input outputVariable serialization rules

Java Core Classes and Threads Questions

Multiple choice

How many subclasses are there of the InputStream class?

  1. 9

  2. 8

  3. 7

  4. 6

  5. 5
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

This is the correct answer. There are 7 subclasses of the InputStream class. These are:

  1. FileInputStream for reading bytes from a file.
  2. ObjectInputStream for readin objects and primitive data types from input stream.
  3. SequenceInputStream for readin from a sequence of streams.
  4. ByteArrayInputStream for Stream that reads a byte array.
  5. pipedInputStream for reading from a piped stream.
  6. FilterInputStream for filtering input from Existing Stream.
  7. StringBufferInputStream for reading from a string.
Multiple choice

How many subclasses of the OutputStream Class are present in Java?

  1. 9

  2. 6

  3. 5

  4. 8

  5. 7
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

There five subclasses of the OutputStream class are:

  1. FileOutputStream for writing bytes into file
  2. ObjectOutputStream for writing objects and primitive data types to output stream.
  3. ByteArrayOutputStream for output stream that writes byte into array.
  4. pipedOutputStream for writing into a piped stream.
  5. FilterOutputStream for filtering output into an existing stream. So, this is the correct answer.
Multiple choice

Which of the following is/are not the subclasses of the Reader class?

  1. StringReader

  2. PipeReader

  3. InputReader

  4. Both (1) and (2)

  5. Both (1) and (3)
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

There is no subclass of Reader class named InputReader. The correct name is InputStreamReader used for reading a character stream. So, this is the correct answer according to the question.

Multiple choice

How many subclasses of the Reader Class are there in Java?

  1. 9

  2. 8

  3. 7

  4. 6

  5. 5
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

There are 6 subclasses of reader Class in Java. These are:

  1. BufferedReader for buffering other readers
  2. ChararrayReader for reading from char array
  3. FilterReader for reading filter streams
  4. InputStreamReader for reading a character stream
  5. PipedReader for reading from pipe
  6. StringReader for reading from a string So, this is the correct answer.
Multiple choice

How many subclasses of the Writer class are there in Java?

  1. 7

  2. 6

  3. 8

  4. 9

  5. 5
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

There are 7 subclasses of the Writer class in Java. These are:

  1. OutputStreamWrite for writing a character stream
  2. BufferedWriter for buffering other writers
  3. PrintWriter for writing formatted data
  4. PipedWriter for writing to a pipe
  5. CharArrayWriter for writing to a char array
  6. StringWriter for writing to a string
  7. FilterWriter for writing filtered streams. So, this is the correct answer.