Computer Knowledge

Java Core Classes and Threads

1,935 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 methods of a String class is used to compare the given string “str1” to another string “str2” by ignoring the case consideration?

  1. str1.equals(str2);

  2. str1.equalsIgnoreCase(str2)

  3. str1.equalignoreCase(str2)

  4. str1.equalsIgnorecase(str2)
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The method equlaIgnoreCase() is used to compare the given string to another string by ignoring the case consideration. Hence, to compare str1 and str2, the statement will be as follows: str1.equalsIgnorecase(str2);

Multiple choice

Which of the following methods is used to get the index within the given string “str” at the first occurrence of the specified substring “str1”?

  1. str1.indexOf(int ch,int from Index)

  2. str1.indexOf(String str)

  3. str.indexOf(string str1)

  4. str.indexOf(String str1)
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The method indexOf() is used to get the index within the given string “str” at the first occurrence of the specified substring “str1”. Hence, the statement will be str.indexOf(String str1);

Multiple choice

What is the method used to convert String variable to primitive integer

  1. Integer.parseInt(String str)

  2. Integer.convertInt(String str)

  3. Integer.valueOf(String str)

  4. Integer.toInteger(String str)
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This answer is correct. To convert a String to a primitive integer, static method parseInt(String str) is executed. This will take the String variable and convert to primitive integer

Multiple choice

Which method is not overridden by Annotation interface?

  1. hashCode()

  2. equals()

  3. clone()

  4. toString()
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

This answer is correct. Annotation interface overrides only three methods hashCode(), toString() and equals() methods. All the methods in Object class other than hashCode(), toString() and equals() are not overridden by the Annotation interface.

Multiple choice

Which two statements are true about properly overridden hashCode() and equals() methods?

  1. hashCode() doesn't have to be overridden if equals() is.
  2. equals() doesn't have to be overridden if hashCode() is.
  3. hashCode() can always return the same value, regardless of the object that invoked it.
  4. equals() can be true even if it's comparing different objects.

  1. 1 and 2

  2. 2 and 3

  3. 3 and 4

  4. 1 and 3
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Statements (3) and (4) are correct. Statements (1) and (2) are incorrect because hashCode() and equals() can't be overridden.

Multiple choice

Which of the following are true regarding dynamic method dispatch? i. Dynamic method dispatch is a process in which a call to an overridden method is resolved at runtime rather than at compile time. ii. Dynamic method dispatch is a process in which a call to an overridden method is resolved at compile time rather than at runtime. iii. In Dynamic method dispatch process, a reference variable calls the overridden method of a superclass. iv. In Dynamic method dispatch process, a reference variable calls the overridden method of a subclass.

  1. i. and iv. are correct

  2. i. and iii. are correct

  3. ii. and iii. are correct

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

The dynamic dispatch process is a process which is applicable when  a call to the overridden method is resolved at runtime rather than at compile time. This will be used as part of polymorphism concept. In the dynamic dispatch process, a reference variable calls the overridden method of the superclass but not the subclass because it doesn't know anything about subclass.