5 inadequate Java job interview questions

Would you like to work for the company after such questions?

The questions were taken from the lecture on JPoint 2016.

Questions first, then answers and explanations. Try to ask questions on your own.

There may be multiple answers.

Question #1

Which line(s) will print false? 1, 2, or 3?

Question #2

Which method will be executed? 1, 2, 3, or Compile error?

Question #3

What string will be printed during the execution of run() method?

• My search engine:
• My search engine: http://www.google.com
• Program will freeze
• Compile error

Question #4

Which line(s) will print true? 1, 2, or 3?

Question #5

Which line(s) will print true? 1, 2, both, or none of them?

Answers and explanations

Question #1

equals() method implementation in String

Line #1 doesn’t even compile because there’s type mismatch between String and StringBuilder.

Line #2 gives false because the second object should be String as well.

Line #3 prints false as well because StringBuilder doesn’t have implemented equals() method.

Question #2

There’s just a rule: methods with vararg parameter have the least priority. And the number casting operation has more priority than boxing operation. That’s why the answer is 2.

Question #3

In Java we can create labels like label: . This feature helps us to break outer loops. Here’s a good and short explanation:

How to use labels in java code?

So, this code will run correctly and print us My search engine:.

Question #4

Line #1 will print true because when we initialized "hello" the first time in s1, the string gets to the string pool. And instead of creating a new string for s4, Java just takes the existing string from the string pool. And that’s why s1 and s4 link to the same object.

Line #2 will print false because when we have a non-final string in concatenation we create a new object.

Line #3 gives true because when we use only final strings and literals, concatenation happens during compile time.

Question #5

valueOf(..) implementation in Long.

Let’s go deeper into Java source code of Long class. As we know, Java uses valueOf(..) method to autobox primitive number values. And if we take a look at the implementation of the method, we can see that while autoboxing of 111L Java caches our number and doesn’t create a new object. In most wrapper classes Java caches numbers between -128 and 127.

That’s why 1st line prints true and 2nd - false .

These 5 questions tell us that Java is huge and it’s almost impossible to know everything.

Nevertheless, hope you’ve leveled up your Java knowledge a bit.

I have :)