Core Java Quiz

Filed Under: Java

Welcome to Core Java Quiz. Java is an object-oriented programming language.

Core Java Quiz

In this quiz, you will be tested on Core Java basics and OOPS concepts. There are some code snippets too to test your basic Java coding skills.

Some of the questions have multiple answers. You can click on the “Reveal Answer” button for the correct answer and explanation.

Give it a try and share it with others if you like it.

1. Which of the below is valid way to instantiate an array in java?

A. int myArray [] = {1, 3, 5}; 
B. int myArray [] [] = {1,2,3,4}; 
C. int [] myArray = (5, 4, 3); 
D. int [] myArray = {“1”, “2”, “3”};

Click to Reveal Answer

Correct Answer: A

int [] myArray = {“1”, “2”, “3”}; is invalid because String can’t be converted to an int.

int [] myArray = (5, 4, 3); is invalid because array elements should be defined in curly braces ({}).

int myArray [] [] = {1,2,3,4}; is invalid because myArray is a two-dimensional array whereas in this case it’s being defined as a one-dimensional array. The compiler will complain as Type mismatch: cannot convert from int to int[].

2. Which of the below are reserved keyword in Java?

A. array
B. goto
C. null
D. int

Click to Reveal Answer

Correct Answer: B, D

The goto and int are reserved keywords in java. array and null are not keywords in java.

3. What will happen if we try to compile and run below program?

interface Foo{ int x = 10;}

public class Test { 
    public static void main(String[] args) { 
        Foo.x = 20; 
        System.out.println(Foo.x); 
    }
}

A. Prints 10 
B. Prints 20 
C. Compile Time Error 
D. Runtime error because Foo.x is final.

Click to Reveal Answer

Correct Answer: C

By default, any field of the interface is public, static, and final. So we can’t change is, hence compile-time error at the statement Foo.x = 20;.

4. What will be the output of the below program?

public class Test {
	public static void main(String[] args) {
		char c = 65;
		System.out.println("c = " + c);
	}
}

A. Compile Time Error 
B. Prints “c = A” 
C. Runtime Error 
D. Prints “c = 65”

Click to Reveal Answer

Correct Answer: B

Java compiler tries to automatically convert int to char. Since 65 gets converted to A, hence output will be “c = A”. The char values range is from u0000 to uffff. So char c = 65535; is valid but char c = 65536; will give compile time error.

5. What will be output of below program?

public class Test { 
    public void main(String[] args) {
        int x = 10*20-20; 
        System.out.println(x); 
    }
}

A. Runtime Error
B. Prints 180
C. Prints 0
D. Compile-time error.

Click to Reveal Answer

Correct Answer: A

Runtime error because main method is not static. The error message will be Main method is not static in class Test, please define the main method as: public static void main(String[] args)

6. What are the valid statements for static keyword in Java?

A. We can have static block in a class. 
B. The static block in a class is executed every time an object of class is created.
C. We can have static method implementations in interface.
D. We can define static block inside a method.

Click to Reveal Answer

Correct Answers: A, C

We can have static block in a class, it gets executed only once when class loads. From java 8 onwards, we can have static method implementations in interfaces.

7. Select all the core concepts of OOPS.

A. Abstraction
B. Inheritance
C. Interface
D. Polymorphism
E. Generics

Click to Reveal Answer

Correct Answers: A, B, D

OOPS core concepts are;

  1. Abstraction
  2. Encapsulation
  3. Polymorphism
  4. Inheritance
  5. Composition
  6. Association
  7. Aggregation

Read more at OOPS Concepts

8. Which of the following statements are true for inheritance in Java?

A. The “extend” keyword is used to extend a class in java.
B. You can extend multiple classes in java.
C. Private members of the superclass are accessible to the subclass.
D. We can’t extend Final classes in java.

Click to Reveal Answer

Correct Answer: D

Inheritance is one of the core concepts in Java. You should be familiar with it. Please read the following articles to learn more about the answer choices – Inheritance in Java, Multiple Inheritance in Java.

9. What will be the output of below program?

package com.journaldev.java;

public class Test {
	public static void main(String[] args) {
		Super s = new Subclass();
		s.foo();
	}
}

class Super {
	void foo() {
		System.out.println("Super");
	}
}

class Subclass extends Super {
	static void foo() {
		System.out.println("Subclass");
	}
}

A. Compile time error
B. Super
C. Subclass
D. Runtime error

Click to Reveal Answer

Correct Answer: A

Subclass foo() method can’t be static, it will give compile time error This static method cannot hide the instance method from Super.

10. What will be the output of below program?

package com.journaldev.java;

public class Test {
	public static void main(String[] args) {
		Subclass s1 = new Subclass();
		s1.foo(); // line 6
		Super s = new Subclass();
		s.foo(); // line 8
	}
}

class Super {
	private void foo() {
		System.out.println("Super");
	}
}

class Subclass extends Super {
	public void foo() {
		System.out.println("Subclass");
	}
}

A. Compile time error at line 6
B. Compile time error at line 8
C. Compile time error at both line 6 and 8
D. Works fine and prints “Subclass” two times.

Click to Reveal Answer

Correct Answer: B

Compile time error at line 8 because Super class foo() method is private. The error message is The method foo() from the type Super is not visible.

11. What will be the output of below program?

import java.io.IOException;

public class Test {
	public static void main(String[] args) {
		try {
			throw new IOException("Hello");
		} catch (IOException | Exception e) {
			System.out.println(e.getMessage());
		}
	}
}

A. Compile-time error
B. Prints “Hello”
C. Runtime Error

Click to Reveal Answer

Correct Answer: A

Compile-time error as The exception IOException is already caught by the alternative Exception.

12. What will be the output of below program?

public class Test {
	public static void main(String[] args) {
		String x = "abc";
		String y = "abc";
		x.concat(y);
		System.out.print(x);
	}
}

A. abcabc
B. abc
C. null

Click to Reveal Answer

Correct Answer: B

x.concat(y); will create a new string but it’s not assigned to x, so the value of x is not changed.

13. Which of the below are unchecked exceptions in java?

A. RuntimeException
B. ClassCastException
C. NullPointerException
D. IOException

Click to Reveal Answer

Correct Answer: A, B, C

RuntimeException and its subclasses are unchecked exceptions. Unchecked exceptions do not need to be declared in a method or constructor’s throws clause.

14. What will be the output of below program?

package com.journaldev.java;

import java.io.IOException;

public class Test {
	public static void main(String[] args) {
		try {
			throw new Exception("Hello ");
		} catch (Exception e) {
			System.out.print(e.getMessage());
		} catch (IOException e) {
			System.out.print(e.getMessage());
		} finally {
			System.out.println("World");
		}
	}
}

A. Compile-time error
B. Hello
C. Hello World
D. Hello Hello World

Click to Reveal Answer

Correct Answer: A

Compile-time error Unreachable catch block for IOException. It is already handled by the catch block for Exception.

15. Which of the following statement(s) are true for java?

A. JVM is responsible for converting Byte code to the machine-specific code.
B. We only need JRE to run java programs.
C. JDK is required to compile java programs.
D. JRE doesn’t contain JVM

Click to Reveal Answer

Correct Answer: A, B, C

For a complete explanation, read JDK, JRE, and JVM.

16. Can we have two main methods in a java class?

A. Yes
B. No

Click to Reveal Answer

Correct Answer: A

This was a tricky question. We can have multiple methods having name as “main” in java through method overloading.

17. Which of the following statements are true about annotations in java?

A. @interface keyword is used to create custom annotation
B. @Override is a built-in annotation in java
C. Annotations can’t be applied to fields in a class.
D. @Retention is one of the meta annotation in java.
E. Java annotation information gets lost when class is compiled.

Click to Reveal Answer

Correct Answer: A, B, D

For a complete explanation, read Java Annotations.

18. Which of the following statements are true about Enum in java?

A. All java enum implicitly extends java.lang.Enum class.
B. Java enum can implement interfaces.
C. We can create instance of enum using new operator.
D. Enums can’t be used in switch statements.
E. Enum constants are implicitly static and final.

Click to Reveal Answer

Correct Answer: A, B, E

Read more at Enum in Java.

19. Which of the below are built-in class loaders in java?

A. Bootstrap Class Loader
B. Extensions Class Loader
C. Runtime Class Loader
D. System Class Loader

Click to Reveal Answer

Correct Answer: A, B, D

Read more at Classloaders in Java.

20. What will be the output of below program?

package com.journaldev.util;

public class Test {
	public static String toString() {
		System.out.println("Test toString called");
		return "";
	}

	public static void main(String args[]) {
		System.out.println(toString());
	}
}

A. “Test toString called”
B. Compile-time error
C. “Test@7fh2bd8” (Object class toString() method is being called)

Click to Reveal Answer

Correct Answer: B

We will get a compile-time error because we can’t have an Object class method overridden with the static keyword. The Object class has toString() method. You will get a compile-time error as “This static method cannot hide the instance method from Object”.

21. What will be the output of below program?

public class Test {
	public static void main(String[] args) {
		String s1 = "abc";
		String s2 = "abc";
		System.out.println("s1 == s2 is:" + s1 == s2);
	}
}

A. s1 == s2 is:true
B. false
C. s1 == s2 is:false
D. true

Click to Reveal Answer

Correct Answer: B

The given statements output will be “false” because in java + operator precedence is more than == operator. So the given expression will be evaluated to “s1 == s2 is:abc” == “abc” i.e false.

Conclusion

I hope you liked the Core Java Quiz. If you think I have missed some important areas, let me know and I will add some more tricky quiz questions here.

Next Quiz: Java String Quiz

Comments

  1. azin says:

    great work, thanks

  2. Dragos Todoroscean says:

    LOL , at first question , answer is wrong
    The correct will be int[] array={1,2,3};
    Not int array[] = {1,2,3};

    1. Pankaj says:

      Did you ever try to run it? I did and here it is from the Shell.

      jshell> int myArray [] = {1, 3, 5};
      myArray ==> int[3] { 1, 3, 5 }
      
      jshell> int[] array={1,2,3};
      array ==> int[3] { 1, 2, 3 }
      
      jshell> int array[] = {1,2,3};
      array ==> int[3] { 1, 2, 3 }
      
      1. Azin says:

        the page shows “There is no question” for me, in all the quizzes! why?

        1. Pankaj says:

          There was some issue, which has been fixed now.

          1. azin says:

            Thanks, for Question 5, there is no main method in the code, that be static or not

          2. Pankaj says:

            Ah, I mistakenly removed it while doing some editing. I have fixed it.

  3. joey says:

    The JRE includes the JVM, which is what actually interprets the byte code and runs your program. To do this the JVM uses libraries and other files provided by the JRE.

  4. Achyut says:

    in question 4 i have copy your code and getting out is ‘c = A’ i have selected that option only but it says wrong option

    1. Pankaj says:

      Sorry about that, some error happened when I was editing the question. I have fixed it.

  5. Naseem Ahamed says:

    Thanks for the quiz. 15th question blew my mind!

  6. Nate says:

    I’m not sure what java version this was written against, but you most certainly can use Enums in switch statements. You couldn’t use strings in switch statements before Java 7, but even before that you could use Enums. Even the link in the description for why “Enums can’t be used in switch statements.” says that they can be used in switch statements.

    1. Pankaj says:

      Yes, you are right and so does the question. You have to select statements that are true for Enum.

  7. Tom says:

    Java Runtime Environment (JRE) contains JVM, class libraries, and other supporting files.

  8. Khyn Harold Jay Antoque says:

    Do you have a source code when making this quiz, did you use php for this?

  9. nisha says:

    Hello Pankaj,
    Your site has some problem. I have attempted only 5 questions, and finished my quiz.but it showing all the questions are attempted. with incorrect answer.

    1. Pankaj says:

      Yes, when you finished the quiz. Any question you didn’t attempted will be considered as incorrectly answered. Just like any exams, if you won’t provide answer to a question, you won’t get any marks for it.

  10. Enrico says:

    Are you sure about question 8? I just copied and paste your code on IntelliJ and I got compilation error.

  11. Hubert says:

    Question 6>> WRONG>> My output is Super! I get an error, too, but the question was >> What will be the output of below program?

    1. Pankaj says:

      Did you run the code in Eclipse, use command line and you will see that output is correct? Check this thread to understand why you got the output.
      https://stackoverflow.com/questions/49633887/compiler-error-but-program-executes-fine

    2. Ram Sharan says:

      Looks like Pankaj sir has made some changes to this set of questions. Earlier I was completely correct, but now the marked answers are showing as the wrong answer but explanation is correct. I also did google and tried output code in eclipse. I am double sure about this mistake.
      Pankaj sir plz cross check this issue. The explanation shows correct answers and I have marked same answer but it’s highlighted by red color.

  12. Eswar says:

    One of the questions were to select java core concepts from the options. One of the options were ‘Generics’ which was actually a link to Generics page. When I accidentally clicked on it, it took me to another page. Due to this, I could not complete the quiz. Please remove that link so that it won’t happen again for others.

    1. Pankaj says:

      Thanks for letting us know, i have fixed it.

  13. kaka says:

    This is a good warm up quiz. I realised I still have so many things to do

  14. Raviraj BK says:

    It was very good quiz!! 🙂 Awesome work

  15. koreanOppa says:

    This was an interesting quiz for me. I just found out I need more practice in Java.

  16. Yannick loic says:

    Very instructive

  17. java reader says:

    Good questions

  18. Jawad Ali says:

    Thanks a lot for the effort put to make this quiz. Really helped refresh all the basics.

    Now that I have got a taste for a quality quiz, I would love to see similar quiz for more advanced topics like Collections and Threads.

    Once again, Great work! Thanks.

  19. Sujoy says:

    Good questions. The best part was the explanation of the quiz answers at the end for review.

  20. Anita says:

    Nice to learn via Quiz!

  21. Rhushikesh says:

    Where to start quiz. I am not able to see any link

    1. Pankaj says:

      I was editing the Quiz questions, so it was unavailable for some time. It’s back up again now, please give it a try. Thanks.

  22. Peter Alexay says:

    Good questions! Thanks for your quiz.

  23. Svetik says:

    Thanks for this great test! It showed me a lot of gaps in my knowledge! It would be great to have some more ! 🙂

  24. Luis Bravo says:

    Greetings from Venezuela, good job

  25. vikash says:

    doing good job sir

  26. Niranjan Kumaar says:

    Hi
    I need SQL program like many to one, one to one, one to many on different different kind. who has been asked in interview …

  27. Alex says:

    Description of answer to question 11 about multiple exceptions handling depends on language level, although it’s сompile time error in any case.
    java multi-catch statement is not supported in -source 1.6

    1. Pankaj says:

      Hi Alex,

      Any programming test always assume the latest version. For example, if you have a lambda program, you shouldn’t say that output depends on whether you are on java 8 or lower.

  28. Aly says:

    Good job! Thanks.
    Only one remark:
    question ” Can we have two main methods in a java class?” The answer no is incorrect.
    Because yes, we can have 2 methods, for example:
    public class A {
    public static void main( Stting [] args) {}
    public void main( int[] args) {}
    }
    Why not?)

    1. Pankaj says:

      I think you didn’t checked the question properly, you are iterating the same thing in the question explanation.

  29. rahul malgujar says:

    good job…a very good medium for begineers .

  30. Miguel Torres says:

    Excellent JAVA Core quiz. I realized that I need to practice more the basic topics, We apreciate all your efforts. Thanks

    Regards

  31. Yevgeny says:

    The quiz is very good but IMO it contains mistakes. “null” cannot be used as a name of variable.Therefore, it is a reserved word in Java. This is output from javac.

    test.java: error: expected
    String null;
    ^

      1. pa1 says:

        true, false, and null might seem like keywords, but they are actually literals; you cannot use them as identifiers in your programs.

      2. Rita says:

        Hi Pankaj,
        Goto statement is not applicable in JAVA so how goto is keyword for JAVA

  32. Williams Ramos Horizonte says:

    excelent

  33. Unamuno says:

    Even if you use a multiple choice approach, the answer may not be true or false.
    Example given: You asked for java keywords, and rated my answer incorrect. But null is no keyword, nbut the null literal. I noticed several of such things but did’nt took the time to write everything down.
    I’ll visit again and try to give more comments.
    Thanks for your efforts, it helps in preparing very simple tasks.
    But they’re far away from what I excpect fromwhat I expect students at my university to master once they have terminated their bachelor courses.

    1. Pankaj says:

      The question and answers for java keywords are correct, let me drop you an email for this.

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