80 interview questions on Java for developers (2026)

Hard

17 votes3605 runs

1 comment

How many times is the condition `(a++ < 15)` evaluated in the following code? ```java int a = 3; while (a++ < 15) { if ((a++ % 5) == 0) break; } ```

Back-end developer

loops

control flow

Thomas De verdièreat Dec 16, 2021

Hard

14 votes3624 runs1 comment

Serialization can be customized with the Externalizable interface

Back-end developer

serialization

interface

Thomas De verdièreat Jan 4, 2022

Hard

14 votes3554 runs0 comment

A monitor in Java

Back-end developer

java

thread

Thomas De verdièreat Jan 4, 2022

Easy

14 votes3506 runs0 comment

What does the final keyword mean in front of a method in Java?

Back-end developer

java

methods

Thomas De verdièreat Jan 4, 2022

Hard

14 votes3445 runs0 comment

How many instance of Integer cannot be freed from memory?

Back-end developer

array

memory

Thomas De verdièreat Dec 16, 2021

Hard

12 votes3645 runs0 comment

A Customer class has the com.company.model package.

Back-end developer

inheritance

package

Thomas De verdièreat Jan 4, 2022

Hard

12 votes3606 runs

1 comment

What is the error message when you try to serialize a class that does not implement Serializable?

Back-end developer

java

serialization

Thomas De verdièreat Dec 2, 2021

Hard

11 votes3600 runs0 comment

A “synchronized” method

Back-end developer

java

method

Thomas De verdièreat Jan 4, 2022

Hard

11 votes3501 runs0 comment

What "design pattern" makes it possible to offer a means of treating the elements of a tree without worrying about the course?

Back-end developer

design pattern

tree

Thomas De verdièreat Jan 4, 2022

Easy

9 votes3422 runs0 comment

Which of these classes is the most suitable for composing a character string from several elements concatenated to each other?

Back-end developer

string

java

Thomas De verdièreat Jan 4, 2022

Medium

9 votes3392 runs2 comments

What does the following code show?

Back-end developer

java

variable

Thomas De verdièreat Jan 4, 2022

Hard

8 votes3588 runs0 comment

Write a finalizer in Java.

Back-end developer

java

finalizer

Thomas De verdièreat Dec 16, 2021

Easy

8 votes3456 runs0 comment

What is the classpath for?

Back-end developer

java

classpath

Thomas De verdièreat Jan 4, 2022

Easy

8 votes3401 runs0 comment

Java 5: where to place the "@Override" tag and why?

Back-end developer

java

annotations

Thomas De verdièreat Jan 4, 2022

Easy

7 votes3509 runs

2 comments

What package contains the HashMap class in Java?

Back-end developer

java

hashmap

Thomas De verdièreat Jan 4, 2022

Easy

7 votes3481 runs0 comment

Create an instance of ArrayList in Java

Back-end developer

array

list

Thomas De verdièreat Jan 4, 2022

Hard

7 votes3474 runs1 comment

What is the superclass of Integer, Long, Byte, BigDecimal and Short in Java?

Back-end developer

java

superclass

Thomas De verdièreat Jan 4, 2022

Easy

7 votes3415 runs0 comment

What design pattern will you use to dynamically add capabilities to an object in Java?

Back-end developer

design patterns

object

Thomas De verdièreat Jan 4, 2022

Hard

6 votes3611 runs

3 comments

How to write a portable Java program

Back-end developer

java

native

Thomas De verdièreat Jan 4, 2022

Hard

6 votes3557 runs0 comment

How to create a thread in Java

Back-end developer

threads

java

Thomas De verdièreat Jan 4, 2022

80 interview questions on Javafor developers (2026)

Test your technical skills before an interview of Java with 80 corrected questions. Beginner, Intermediate or Expert level.

How many times is the condition `(a++ < 15)` evaluated in the following code? ```java int a = 3; while (a++ < 15) { if ((a++ % 5) == 0) break; } ```

Serialization can be customized with the Externalizable interface

A monitor in Java

What does the final keyword mean in front of a method in Java?

How many instance of Integer cannot be freed from memory?

A Customer class has the com.company.model package.

What is the error message when you try to serialize a class that does not implement Serializable?

A “synchronized” method

What "design pattern" makes it possible to offer a means of treating the elements of a tree without worrying about the course?

Which of these classes is the most suitable for composing a character string from several elements concatenated to each other?

What does the following code show?

Write a finalizer in Java.

What is the classpath for?

Java 5: where to place the "@Override" tag and why?

What package contains the HashMap class in Java?

Create an instance of ArrayList in Java

What is the superclass of Integer, Long, Byte, BigDecimal and Short in Java?

What design pattern will you use to dynamically add capabilities to an object in Java?

How to write a portable Java program

How to create a thread in Java