You will always see some interview questions from Exception and Error handling in core Java Interviews. Exception handling is an important aspect of Java application development and its key to writing robust, stable Java programs, which makes it natural favorites on interviews. Questions from Error and Exception in Java mostly based on concept of Exception and Error in Java, How to handle Exception , best practices to follow during Exception handling etc. Though multithreading, garbage collection, JVM concepts and questions from object oriented design rules these interviews, you should always expect and prepare some questions on effective error handling. Some Interviewer also test debugging skill of programmers, as resolving Exceptions quickly is another trait of solid Java programming knowledge. If programmer is familiar with infamous and dodgy ClassNotFoundExceptionor OutOfMemoryError, there is a good chance that he has some good practical experience under his belt. In this article we will see some Java Error and Exception interview questions asked to fresher, experienced and senior Java developers in Java J2EE interviews.
Java Exception and Error Interview Questions
Java Exception and Error Interview Question AnswersHere is my list of frequently asked questions from Java Error and Exception topics in various programming interviews to Java and J2EE developers. I have also shared my answers for these questions for quick revision, and provided source for more in depth understanding. I have tried to include questions of various difficulty level, including simplest of simple for freshers and some tricky questions for senior Java developers. If you think, there is a good question, which is not included in this list, please feel free to share it via comment. You can also share error handling questions asked to you on interviews or any question, for which you don’t know the answer.
1) What is Exception in Java?
This is always been first interview question on Exception and mostly asked on fresher level interviews. I haven't seen anybody asking about what is Exception in senior and experienced level interviews, but this is quite popular at entry level. In simple word Exception is Java’s way to convey both system and programming errors. In Java Exception feature is implemented by using class like Throwable, Exception, RuntimeException and keywords like throw, throws, try, catch and finally. All Exception are derived form Throwable class. Throwable further divides errors in too category one is java.lang.Exception and other is java.lang.Error. java.lang.Error deals with system errors like java.lang.StackOverFlowError or Java.lang.OutOfMemoryError while Exception is mostly used to deal with programming mistakes, non availability of requested resource etc.
2) What is difference between Checked and Unchecked Exception in Java ?
This is another popular Java Exception interview question appears in almost all level of Java interviews. Main difference between Checked and Unchecked Exception lies in there handling. Checked Exception requires to be handled at compile time using try, catch and finally keywords or else compiler will flag error. This is not a requirement for Unchecked Exceptions. Also all exceptions derived from java.lang.Exception classes are checked exception, exception those which extends RuntimeException, these are known as unchecked exception in Java. You can also check next article for more differences between Checked and Unchecked Exception.
3) What is similarity between NullPointerException and ArrayIndexOutOfBoundException in Java?
This is Java Exception interview question was not very popular, but appears in various fresher level interviews, to see whether candidate is familiar with concept of checked and unchecked exception or not. By the way answer of this interview question is both of them are example of unchecked exception and derived form RuntimeException. This question also opens door for difference of array in Java and C programming language, as arrays in C are unbounded and never throw ArrayIndexOutOfBoundException.
4) What best practices you follow while doing Exception handling in Java ?
This Exception interview question in Java is very popular while hiring senior java developer of Technical Lead. Since exception handling is crucial part of project design and good knowledge of this is desirable. There are lot of best practices, which can help to make your code robust and flexible at same time, here are few of them:
1) Returning boolean instead of returning null to avoid NullPointerException at callers end. Since NPE is most infamous of all Java exceptions, there are lot of techniques and coding best practices to minimize NullPointerException. You can check that link for some specific examples.
2) Non empty catch blocks. Empty catch blocks are considered as one of the bad practices in Exception handling because they just ate Exception without any clue, at bare minimum print stack trace but you should do alternative operation which make sense or defined by requirements.
3) Prefer Unchecked exception over checked until you have a very good reason of not to do so. it improves readability of
code by removing boiler plate exception handling code
.
4) Never let your database Exception flowing till client error. since most of application deal with database and SQLException is a checked Exception in Java you should consider handling any database related errors in DAO layer of your application and only returning alternative value or something meaningful RuntimeException which client can understand and take action.
5) calling close() methods for connections, statements, and streams on finally block in Java.
I have already shared lot of these in my post Top 10 Java exception handling best practices, you can also refer that for more knowledge on this topic.
Java Exception and Error Interview Questions
Java Exception and Error Interview Question AnswersHere is my list of frequently asked questions from Java Error and Exception topics in various programming interviews to Java and J2EE developers. I have also shared my answers for these questions for quick revision, and provided source for more in depth understanding. I have tried to include questions of various difficulty level, including simplest of simple for freshers and some tricky questions for senior Java developers. If you think, there is a good question, which is not included in this list, please feel free to share it via comment. You can also share error handling questions asked to you on interviews or any question, for which you don’t know the answer.
1) What is Exception in Java?
This is always been first interview question on Exception and mostly asked on fresher level interviews. I haven't seen anybody asking about what is Exception in senior and experienced level interviews, but this is quite popular at entry level. In simple word Exception is Java’s way to convey both system and programming errors. In Java Exception feature is implemented by using class like Throwable, Exception, RuntimeException and keywords like throw, throws, try, catch and finally. All Exception are derived form Throwable class. Throwable further divides errors in too category one is java.lang.Exception and other is java.lang.Error. java.lang.Error deals with system errors like java.lang.StackOverFlowError or Java.lang.OutOfMemoryError while Exception is mostly used to deal with programming mistakes, non availability of requested resource etc.
2) What is difference between Checked and Unchecked Exception in Java ?
This is another popular Java Exception interview question appears in almost all level of Java interviews. Main difference between Checked and Unchecked Exception lies in there handling. Checked Exception requires to be handled at compile time using try, catch and finally keywords or else compiler will flag error. This is not a requirement for Unchecked Exceptions. Also all exceptions derived from java.lang.Exception classes are checked exception, exception those which extends RuntimeException, these are known as unchecked exception in Java. You can also check next article for more differences between Checked and Unchecked Exception.
3) What is similarity between NullPointerException and ArrayIndexOutOfBoundException in Java?
This is Java Exception interview question was not very popular, but appears in various fresher level interviews, to see whether candidate is familiar with concept of checked and unchecked exception or not. By the way answer of this interview question is both of them are example of unchecked exception and derived form RuntimeException. This question also opens door for difference of array in Java and C programming language, as arrays in C are unbounded and never throw ArrayIndexOutOfBoundException.
4) What best practices you follow while doing Exception handling in Java ?
This Exception interview question in Java is very popular while hiring senior java developer of Technical Lead. Since exception handling is crucial part of project design and good knowledge of this is desirable. There are lot of best practices, which can help to make your code robust and flexible at same time, here are few of them:
1) Returning boolean instead of returning null to avoid NullPointerException at callers end. Since NPE is most infamous of all Java exceptions, there are lot of techniques and coding best practices to minimize NullPointerException. You can check that link for some specific examples.
2) Non empty catch blocks. Empty catch blocks are considered as one of the bad practices in Exception handling because they just ate Exception without any clue, at bare minimum print stack trace but you should do alternative operation which make sense or defined by requirements.
3) Prefer Unchecked exception over checked until you have a very good reason of not to do so. it improves readability of
code by removing boiler plate exception handling code
.
4) Never let your database Exception flowing till client error. since most of application deal with database and SQLException is a checked Exception in Java you should consider handling any database related errors in DAO layer of your application and only returning alternative value or something meaningful RuntimeException which client can understand and take action.
5) calling close() methods for connections, statements, and streams on finally block in Java.
I have already shared lot of these in my post Top 10 Java exception handling best practices, you can also refer that for more knowledge on this topic.
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