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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