Have an upcoming technical interview? Here are 37 Java Interview Questions for you to practice with!

1. 37 Java Interview
Practice Questions

2. What is the difference between String,
StringBuffer, and StringBuilder in
Java?
Question 1:

3. How do you run a Java application
on the command line and set the
classpath with multiple jars?
Question 2:

4. What is the difference between final,
finalize, and finally?
Question 3:

5. How does Garbage Collection
prevent a Java application from
going out of memory?
Question 4:

6. What is the difference between a
ClassNotFoundException a n d
NoClassDefFoundError?
Question 5:

7. Why isn't String's .length() accurate?
Question 6:

8. Given two double values d1, d2, why isn’t it reliable to
test their equality using:
Question 7:
d1 == d2

9. What is the problem with this code:
Question 8:
final byte[] bytes = someString.getBytes();

10. What is the JIT?
Question 9:

11. final double d = 1 / 2;
System.out.println(d);
Question 10:
Why does
Print 0? How can you make the code print
0.5 instead?

12. IntStream.range(0, 10).forEach(System.out::println);
Question 11:
In this code:
what is the inferred type of the method
reference System.out::println?

13. final Path path = Paths.get(...);
Files.lines(path).forEach(System.out::println);
Question 12:
What is the problem with this code:

14. What will be the contents of the list after this
operation and why?
Question 13:
final List<Integer> list = new ArrayList<>();
list.add(1);
list.add(2);
list.add(3);
list.remove(2);

15. Write a function to detect if two strings are
anagrams (for example, SAVE and VASE)
Question 14:

16. What is the contract between equals and
hashCode of an object?
Question 15:

17. Can an enum be extended?
Question 16:

18. How threadsafe is enum in Java?
Question 17:

19. How does a JVM handle storing local
variables vs storing objects?
Question 18:

20. Identify the problem in the following code:
Question 19:
public class Foo {
public Foo() {
doSomething();
}
public void doSomething() {
System.out.println("do something acceptable");
}
}
public class Bar extends Foo {
public void doSomething() {
System.out.println("yolo");
Zoom zoom = new Zoom(this);
}
}

21. When do you use volatile variables?
Question 20:

22. Why do you need to use synchronized
methods or blocks?
Question 21:

23. What is the difference between HashMap and
ConcurrentHashMap?
Question 22:

24. When do you need to override the equals
and hashCode methods in Java?
Question 23:

25. What is a service?
Question 24:

26. What is a good usecase of calling
System.gc()?
Question 25:

27. What is the marker interface in Java?
Question 26:

28. How are Annotations better than a Marker
Interfaces?
Question 27:

29. What are checked and unchecked
exceptions? When do you use them?
Question 28:

30. int a = 1L; Won’t compile and
int b = 0; b += 1L; compiles fine.
Why ?
Question 29:

31. Why aren’t you allowed to extend more than
one class in Java but are allowed to
implement multiple interfaces?
Question 30:

32. Question 31:
Test t = null;
t.someMethod();
public static void someMethod() {
...
}
Why doesn’t the following code generate a
NullPointerException even when the
instance is null?

33. Question 32:
public class Test
{
public static void main(String[] args)
{
Integer a = 1000, b = 1000;
System.out.println(a == b);
Integer c = 100, d = 100;
System.out.println(c == d);
}
}
why does the first case print false while the
second case prints true?

34. Question 33:
String s1="home";
String s2="mohe";
How do you check whether or not the following two
strings are anagrams?

35. How do you reverse String("Java
Programming") without using Iterations
and Recursions?
Question 34:

36. Give real world examples of when to use an
ArrayList and when to use LinkedList
Question 35:

37. What is the difference between an Iterator
and a ListIterator?
Question 36:

38. What is the advantage of a generic
collection?
Question 37:

39. Did you know how to answer all 37 questions?
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an experienced Java developer