Welcome to Core Java Quiz. Java is an object oriented programming language. In this quiz, you will be tested on core java basics and OOPS concepts. Give it a try and share with others if you like it. ๐
Core Java Quiz
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- Question 1 of 21
1. Question
Which of the below is valid way to instantiate an array in java?
Correctint [] myArray = {"1", "2", "3"};is invalid because String can’t be converted to int.int [] myArray = (5, 4, 3);is invalid because array elements are defined in curly braces ({}).int myArray [] [] = {1,2,3,4};is invalid because myArray is a two dimensional array whereas it’s being defined as one dimensional array. Compiler will complain asType mismatch: cannot convert from int to int[].Incorrectint [] myArray = {"1", "2", "3"};is invalid because String can’t be converted to int.int [] myArray = (5, 4, 3);is invalid because array elements are defined in curly braces ({}).int myArray [] [] = {1,2,3,4};is invalid because myArray is a two dimensional array whereas it’s being defined as one dimensional array. Compiler will complain asType mismatch: cannot convert from int to int[]. - Question 2 of 21
2. Question
Which of the below are reserved keyword in java?
Correctgotoandintare reserved keywords in java.arrayandnullare not keywords in java.Incorrectgotoandintare reserved keywords in java.arrayandnullare not keywords in java. - Question 3 of 21
3. Question
What will happen if we try to compile and run below program?
Copyinterface Foo{ int x = 10; } public class Test { public static void main(String[] args) { Foo.x = 20; System.out.println(Foo.x); } }CorrectBy default any field of interface is public, static and final. So we can’t change is, hence compile time error at line 8 statement
Foo.x = 20;.IncorrectBy default any field of interface is public, static and final. So we can’t change is, hence compile time error at line 8 statement
Foo.x = 20;. - Question 4 of 21
4. Question
What will be the output of below program?
Copypublic class Test { public static void main(String[] args) { char c = 65; System.out.println("c = "+c); } }CorrectJava compiler tries to automatically convert int to char. Since 65 gets converted to A, hence output will be “c = A”. Note that char are limited to values from \u0000 to \uffff. So
char c = 65535;is valid butchar c = 65536;will give compile time error.IncorrectJava compiler tries to automatically convert int to char. Since 65 gets converted to A, hence output will be “c = A”. Note that char are limited to values from \u0000 to \uffff. So
char c = 65535;is valid butchar c = 65536;will give compile time error. - Question 5 of 21
5. Question
What will be output of below program?
Copypublic class Test { public void main(String[] args) { int x = 10*20-20; System.out.println(x); } }CorrectRuntime error because main method is not static.
Copypankaj:bin pankaj$ java Test Error: Main method is not static in class Test, please define the main method as: public static void main(String[] args)IncorrectRuntime error because main method is not static.
Copypankaj:bin pankaj$ java Test Error: Main method is not static in class Test, please define the main method as: public static void main(String[] args) - Question 6 of 21
6. Question
What are the valid statements for
statickeyword in java?CorrectWe 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.
Further Reading:
IncorrectWe 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.
Further Reading:
- Question 7 of 21
7. Question
Select all the core concepts of OOPS programming.
CorrectOOPS core concepts are;
- Abstraction
- Encapsulation
- Polymorphism
- Inheritance
- Composition
- Association
- Aggregation
Read more at OOPS Concepts
IncorrectOOPS core concepts are;
- Abstraction
- Encapsulation
- Polymorphism
- Inheritance
- Composition
- Association
- Aggregation
Read more at OOPS Concepts
- Question 8 of 21
8. Question
Which of following statements are true for inheritance in java?
CorrectInheritance is one of the core concepts in Java. You should be familiar with it. Please read below articles to learn more about the answer choices.
IncorrectInheritance is one of the core concepts in Java. You should be familiar with it. Please read below articles to learn more about the answer choices.
- Question 9 of 21
9. Question
What will be the output of below program?
Copypackage 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"); } }CorrectSubclass foo() method can’t be static, it will give compile time error
This static method cannot hide the instance method from Super.IncorrectSubclass foo() method can’t be static, it will give compile time error
This static method cannot hide the instance method from Super. - Question 10 of 21
10. Question
What will be the output of below program?
Copypackage com.journaldev.java; public class Test { public static void main(String[] args) { Subclass s1 = new Subclass(); s1.foo(); //line 7 Super s = new Subclass(); s.foo(); // line 10 } } class Super { private void foo() { System.out.println("Super"); } } class Subclass extends Super { public void foo() { System.out.println("Subclass"); } }CorrectCompile time error at line 10 because Super class foo() method is private. Below code snippet shows the compilation error for Java 9.
Copy$javac Test.java Test.java:10: error: foo() has private access in Super s.foo(); ^ 1 error $IncorrectCompile time error at line 10 because Super class foo() method is private. Below code snippet shows the compilation error for Java 9.
Copy$javac Test.java Test.java:10: error: foo() has private access in Super s.foo(); ^ 1 error $ - Question 11 of 21
11. Question
What will be the output of below program?
Copyimport 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()); } } }CorrectCompile time error as
The exception IOException is already caught by the alternative ExceptionIncorrectCompile time error as
The exception IOException is already caught by the alternative Exception - Question 12 of 21
12. Question
What will be the output of below program?
Copypublic class Test { public static void main(String[] args) { String x = "abc"; String y = "abc"; x.concat(y); System.out.print(x); } }Correctx.concat(y);will create a new string but it’s not assigned to x, so value of x is not changed.Incorrectx.concat(y);will create a new string but it’s not assigned to x, so value of x is not changed. - Question 13 of 21
13. Question
Which of the below are unchecked exceptions in java?
CorrectRuntimeException and its subclasses are unchecked exceptions. Unchecked exceptions do not need to be declared in a method or constructor’s throws clause. Read more at Exception Handling in Java
IncorrectRuntimeException and its subclasses are unchecked exceptions. Unchecked exceptions do not need to be declared in a method or constructor’s throws clause. Read more at Exception Handling in Java
- Question 14 of 21
14. Question
What will be the output of below program?
Copypackage 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"); } } }CorrectCompile time error
Unreachable catch block for IOException. It is already handled by the catch block for Exception.IncorrectCompile time error
Unreachable catch block for IOException. It is already handled by the catch block for Exception. - Question 15 of 21
15. Question
Which of the following statement(s) are true for java?
- Question 16 of 21
16. Question
Can we have two main methods in a java class?
CorrectThis was a tricky question. We can have multiple main methods in java through method overloading.
IncorrectThis was a tricky question. We can have multiple main methods in java through method overloading.
- Question 17 of 21
17. Question
Which of the following statements are true about annotations in java?
- Question 18 of 21
18. Question
Which of the following statements are true about Enum in java?
- Question 19 of 21
19. Question
Which of the below are built-in class loaders in java?
- Question 20 of 21
20. Question
What will be the output of below program?
Copypackage 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()); } }CorrectWe will get compile time error because we canโt have an Object class method overridden with static keyword. Note that Object class has
toString()method. You will get compile time error as โThis static method cannot hide the instance method from Objectโ.IncorrectWe will get compile time error because we canโt have an Object class method overridden with static keyword. Note that Object class has
toString()method. You will get compile time error as โThis static method cannot hide the instance method from Objectโ. - Question 21 of 21
21. Question
What will be the output of below program?
Copypublic class Test { public static void main(String[] args) { String s1 = "abc"; String s2 = "abc"; System.out.println("s1 == s2 is:" + s1 == s2); } }CorrectThe 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.
IncorrectThe 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.
Naseem Ahamed says
January 4, 2019 at 1:32 pmThanks for the quiz. 15th question blew my mind!
Nate says
December 12, 2018 at 7:04 amI’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.
Pankaj says
December 13, 2018 at 6:02 amYes, you are right and so does the question. You have to select statements that are true for Enum.
Tom says
October 9, 2018 at 8:18 amJava Runtime Environment (JRE) contains JVM, class libraries, and other supporting files.
Khyn Harold Jay Antoque says
September 24, 2018 at 5:54 amDo you have a source code when making this quiz, did you use php for this?
nisha says
May 3, 2018 at 12:06 amHello 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.
Pankaj says
May 3, 2018 at 12:47 amYes, 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.
Enrico says
April 17, 2018 at 5:53 pmAre you sure about question 8? I just copied and paste your code on IntelliJ and I got compilation error.
Hubert says
April 3, 2018 at 6:21 amQuestion 6>> WRONG>> My output is Super! I get an error, too, but the question was >> What will be the output of below program?
Pankaj says
April 3, 2018 at 9:32 amDid 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
Ram Sharan says
April 19, 2018 at 11:04 amLooks 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.
Eswar says
March 25, 2018 at 9:12 pmOne 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.
Pankaj says
March 26, 2018 at 2:45 amThanks for letting us know, i have fixed it.
kaka says
March 22, 2018 at 7:18 amThis is a good warm up quiz. I realised I still have so many things to do
Raviraj BK says
March 11, 2018 at 3:40 amIt was very good quiz!! ๐ Awesome work
koreanOppa says
February 16, 2018 at 5:45 amThis was an interesting quiz for me. I just found out I need more practice in Java.
Yannick loic says
January 18, 2018 at 10:52 amVery instructive
java reader says
January 17, 2018 at 10:46 pmGood questions
Jawad Ali says
November 29, 2017 at 7:08 pmThanks 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.
Sujoy says
October 15, 2017 at 1:47 amGood questions. The best part was the explanation of the quiz answers at the end for review.
Anita says
October 12, 2017 at 5:57 amNice to learn via Quiz!
Rhushikesh says
September 16, 2017 at 3:41 amWhere to start quiz. I am not able to see any link
Pankaj says
September 16, 2017 at 4:43 amI was editing the Quiz questions, so it was unavailable for some time. It’s back up again now, please give it a try. Thanks.
Peter Alexay says
September 2, 2017 at 7:25 amGood questions! Thanks for your quiz.
Svetik says
August 23, 2017 at 2:55 pmThanks for this great test! It showed me a lot of gaps in my knowledge! It would be great to have some more ! ๐
Luis Bravo says
August 22, 2017 at 11:11 amGreetings from Venezuela, good job
vikash says
August 19, 2017 at 8:48 pmdoing good job sir
Niranjan Kumaar says
August 19, 2017 at 2:13 amHi
I need SQL program like many to one, one to one, one to many on different different kind. who has been asked in interview …
Alex says
August 18, 2017 at 3:49 amDescription of answer to question 11 about multiple exceptions handling depends on language level, although it’s ัompile time error in any case.
java multi-catch statement is not supported in -source 1.6
Pankaj says
August 18, 2017 at 8:32 amHi 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.
Aly says
August 17, 2017 at 11:09 amGood 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?)
Pankaj says
August 17, 2017 at 1:26 pmI think you didn’t checked the question properly, you are iterating the same thing in the question explanation.
rahul malgujar says
August 17, 2017 at 9:45 amgood job…a very good medium for begineers .
Miguel Torres says
August 17, 2017 at 8:40 amExcellent JAVA Core quiz. I realized that I need to practice more the basic topics, We apreciate all your efforts. Thanks
Regards
Yevgeny says
August 17, 2017 at 8:03 amThe 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;
^
Pankaj says
August 17, 2017 at 10:02 amnull is not a reserved keyword, please check below link.
https://docs.oracle.com/javase/tutorial/java/nutsandbolts/_keywords.html
pa1 says
August 17, 2017 at 8:31 pmtrue, false, and null might seem like keywords, but they are actually literals; you cannot use them as identifiers in your programs.
Williams Ramos Horizonte says
August 17, 2017 at 5:46 amexcelent
Unamuno says
August 17, 2017 at 5:03 amEven 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.
Pankaj says
August 17, 2017 at 5:38 amThe question and answers for java keywords are correct, let me drop you an email for this.