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25 interview questions on Java and Craftsmanshipfor developers (2026)

Test your technical skills before an interview of Java and Craftsmanship with 25 corrected questions. Beginner, Intermediate or Expert level.

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25 questions
Easy
5 votes773 runs
1 comment

Write a function that returns the first character of a string in Java

Back-end developer
strings
exceptions
Clément Devos (W3D Team)at Jan 24, 2022
Hard
4 votes550 runs
3 comments

This code allows to randomly get numbers between 1 to 31 in results. Should have declard SimpleDateFormat in the Thread.

Back-end developer
java
thread
date
Clément Devos (W3D Team)at Jan 24, 2022
Expert
1 vote657 runs
2 comments

Java code that replaces keys in a template with their values.

Back-end developer
java
map
string
Clément Devos (W3D Team)at Jan 24, 2022
Easy
1 vote532 runs0 comment

Write a Java code that returns the integer 51

Back-end developer
optional
map
filter
Clément Devos (W3D Team)at Jan 24, 2022
Medium
1 vote508 runs0 comment

Which Java 7 feature was only usable in Java 8?

Back-end developer
java
invoke dynamic
Clément Devos (W3D Team)at Jan 24, 2022
Hard
1 vote497 runs0 comment

A Java class that converts Arabic numbers to Roman numerals.

Back-end developer
java
recursion
map
Clément Devos (W3D Team)at Jan 24, 2022
Medium
1 vote492 runs1 comment

What is the output of the following code? ```java try { return 42; } finally { return 1337; } ```

Back-end developer
exceptions
return
Clément Devos (W3D Team)at Sep 19, 2022
Medium
1 vote492 runs0 comment

Write a Java implementation of the FizzBuzz code kata.

Back-end developer
java
fizzbuzz
Clément Devos (W3D Team)at Jan 24, 2022
Easy
1 vote321 runs1 comment

A code kata is a small exercice thought to train a certain development competence

Back-end developer
code kata
Clément Devos (W3D Team)at Feb 6, 2024
Easy
1 vote171 runs0 comment

What does SRP stand for?

Back-end developer
SOLID principles
Anonymous authorat Nov 26, 2024
Medium
1 vote166 runs0 comment

What is the name of the design pattern used to structure complex applications by considering the problem domain?

Back-end developer
Anonymous authorat Nov 26, 2024
Medium
0 vote538 runs0 comment

Which of these lines compile and would return true?

Back-end developer
strings
intern
Clément Devos (W3D Team)at Jan 24, 2022
Easy
0 vote511 runs0 comment

Immutability mainly allows to avoid side effects and to have thread-safe behaviours.

Back-end developer
java
immutability
Clément Devos (W3D Team)at Jan 24, 2022
Hard
0 vote507 runs0 comment

Write a thread safe singleton in Java

Back-end developer
singleton
thread-safety
Clément Devos (W3D Team)at Sep 19, 2022
Medium
0 vote501 runs0 comment

Explain why the second code compiles but the first one doesn't.

Back-end developer
exceptions
java
Clément Devos (W3D Team)at Jan 24, 2022
Medium
0 vote495 runs0 comment

Calculate 2.00 - 0.99 in Java

Back-end developer
floating point
Clément Devos (W3D Team)at Jan 24, 2022
Medium
0 vote488 runs0 comment

Improve the maintainability of this code by using polymorphism for items.

Back-end developer
java
polymorphism
Clément Devos (W3D Team)at Jan 24, 2022
Medium
0 vote487 runs0 comment

Compare two Java classes with the same fields and methods.

Back-end developer
java
class
record
Clément Devos (W3D Team)at Sep 19, 2022
Easy
0 vote483 runs0 comment

In Java, enums can have methods and attributes.

Back-end developer
enums
Clément Devos (W3D Team)at Jan 24, 2022
Medium
0 vote438 runs0 comment

Find the maximum age of employees in a mall.

Back-end developer
java
stream
flatmap
Clément Devos (W3D Team)at Jan 24, 2022