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

Which of the following options is correct?

i. The Serializable interface has 0 methods ii. The Serializable interface has 1 method iii. The Serializable interface has 2 methods iv. The Serializable interface has 3 methods

  1. i. is true

  2. ii. is true

  3. iii. is true

  4. iv. is true
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This answer is correct because Serializable interface is a marker interface and does not have any methods. This interface when implemented, tells the object serializable tools whether the class is serializable or not.

Multiple choice

What is true from the following options?

i. The Reader/Writer class is character oriented. ii. The Reader/Writer class is byte oriented. iii. The InputStream/OutputStream class is character oriented. iv. The InputStream/OutputStream class is byte oriented.

  1. i. and iii. are true

  2. i. and iv. are true

  3. ii. and iii. are true

  4. ii. and iv. are true.

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

The answer is correct.The Reader/Writer class is used when any manipulation needs to be done on characters whereas InputStream/OutputStream class is used when any manipulation needs to be done on bytes.

Multiple choice

Which of the following options is true?

i. When an object invokes yield() method, it will not return to ready state. ii. When an object invokes yield() method, it will return to ready state. iii. When an object invokes sleep() method, it will return to ready state. iv. When an object invokes sleep() method, it will not return to ready state.

  1. i. and iii. are true

  2. i. and iv. are true

  3. ii. and iii. are true

  4. ii. and iv. are true
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

This answer is correct. When an object invokes yield() method, the object will be ready to perform the next action and so it will be returned to the ready state. When the object calls sleep() method, it will not execute any further action and so it will not be ready to perform next action.

Multiple choice

Pick out what is true from the following options? i. Object instantiated from String Buffer is thread-safe. ii. Object instantiated from String Builder is thread-safe. iii. String Buffer has high and fast performance. iv. String Builder has high and fast performance.

  1. i. and iii. are true.

  2. i. and iv. are true

  3. ii. and iii. are true.

  4. ii. and iv. are true.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

This answer is correct. String Buffer is synchronized or thread-safe and String Builder has higher performance compared to String Buffer.

Multiple choice

What of the following statements is true about NoSuchMethodException?

i. NoSuchMethodException is caused when the method cannot be called. ii. NoSuchMethodException is caused when the method does not exist. iii. NoSuchMethodException is a Checked Exception. iv. NoSuchMethodException is a Unchecked Exception.

  1. i. and iv. are true

  2. i. and iii. are true

  3. ii. and iii. are true

  4. ii. and iv. are true
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

This answer is correct. NoSuchMethodException is caused when the method does not exist. NoSuchMethodException is a Checked Exception.

Multiple choice

Which method is not final in Object class?

  1. getClass()

  2. notify()

  3. notify all()

  4. hashCode()
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

This answer is correct. GetClass(), notify(), notify all() and wait() methods in Object class are declared as final. All other methods can be overridden. HashCode() can be overridden in any class.

Multiple choice

Which of the following is true about ClassNotFoundException?

i. ClassNotFoundException is caused when the class is not found. ii. ClassNotFoundException is caused when the class cannot instantiated. iii. ClassNotFoundException is a Checked Exception. iv. ClassNotFoundException is a Unchecked Exception.

  1. i. and iii. are true

  2. i. and iv. are true

  3. ii. and iii. are true

  4. ii. and iv. are true
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This answer is correct. ClassNotFoundException is caused when the class is not found and it is a checked exception.

Multiple choice

Which of the following methods is not present in the PreparedStatement interface in java database programming?

  1. addBatch()

  2. executeQuery()

  3. executeBatch()

  4. execute()

  5. getMetaData()
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

executeBatch() method is present in the Statement interface and not in PreparedStatement interface and it submits a batch of commands to the database for execution and if all commands execute successfully, returns an array of update counts. So, this answer is true.

Multiple choice

Which of the following methods is present in the Statement interface in java database programming?

  1. isCloseOnInsertion()

  2. isCloseOnCompletion()

  3. isCloseOnDeletion()

  4. isCloseAfterUpdate()

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

isCloseOnCompletion() method is present in the Statement interface. This method returns a value indicating whether this statement will be closed when all its dependent result sets are closed or not. So, this answer is correct.

Multiple choice

How many methods are defined in the Time class in java?

  1. 10

  2. 9

  3. 8

  4. 7

  5. 6
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

There are 10 methods present in the Time class in java. These are:- 1) getDate() 2) getDay() 3) getMonth() 4) getYear() 5) setDate(int i) 6) setMonth(int i) 7) setTime(int i) 8) setYear(int i) 9) toString():- Formats a time in JDBC time escape format 10) valueOf(String s):- Converts a string in JDBC time escape format to a Time value So, this is the correct answer.