Java 8 | Generics | Enums | String Pool | Date API | SQL | Programming
Duration: 20 Minutes
Experience: 3–8 Years
This assessment evaluates Java fundamentals frequently encountered in enterprise applications, including Generics, Enums, String handling, Date/Time API, SQL, and problem-solving skills.
Section A – Java OCP Style MCQs (5 Questions)
Question 1 – String Immutability
What is the output?
public class Test {
public static void main(String[] args) {
String s = "Java";
s.concat("8");
System.out.println(s);
}
}
A. Java
B. Java8
C. 8Java
D. Compilation Error
Question 2 – String Pool
public class Test {
public static void main(String[] args) {
String s1 = "Java";
String s2 = "Java";
String s3 = new String("Java");
System.out.println(
(s1 == s2) + " "
+ (s1 == s3));
}
}
Output?
A.
true true
B.
true false
C.
false false
D.
Compilation Error
Question 3 – Generics
import java.util.*;
public class Test {
public static void main(String[] args) {
List<String> list = new ArrayList<>();
list.add("Java");
Object obj = list.get(0);
System.out.println(obj);
}
}
Output?
A.
Java
B.
Compilation Error
C.
Runtime Exception
D.
null
Question 4 – Enum
enum Status {
NEW,
PROCESSING,
COMPLETED
}
public class Test {
public static void main(String[] args) {
Status status =
Status.valueOf("NEW");
System.out.println(status);
}
}
Output?
A.
NEW
B.
new
C.
Compilation Error
D.
IllegalArgumentException
Question 5 – Java 8 Date API
import java.time.LocalDate;
public class Test {
public static void main(String[] args) {
LocalDate date =
LocalDate.of(2026,7,31);
System.out.println(
date.plusDays(5));
}
}
Output?
A.
2026-08-05
B.
2026-07-36
C.
Compilation Error
D.
Runtime Exception
Section B – SQL Challenge
Question 6
Table
| EMP_ID | NAME | SALARY |
|---|---|---|
| 1 | John | 5000 |
| 2 | Mary | 7000 |
| 3 | Steve | 6500 |
| 4 | David | 4500 |
| 5 | Tom | 8000 |
Query
SELECT *
FROM EMPLOYEE
WHERE SALARY =
(
SELECT MAX(SALARY)
FROM EMPLOYEE
);
Which statement is correct?
A. Returns Tom
B. Returns Mary
C. Returns John
D. Compilation Error
Section C – Programming Questions
Question 7 – Remove Duplicate Characters
Write a Java program to remove duplicate characters from a String while preserving the original order.
Example
programming
Expected Output
progamin
Bonus:
Solve using Java 8 Streams.
Question 8 – Map Sorting
Given
Map<String,Integer> map = Map.of(
"Java",5,
"Spring",8,
"AWS",7,
"Docker",6);
Write a Java 8 program to print the entries in descending order of value.
Expected Output
Spring=8
AWS=7
Docker=6
Java=5
Question 9 – Programming Logic
Write a Java program to determine whether two Strings are rotations of each other.
Example
ABCD
CDAB
Output
true
Example
ABCD
ACBD
Output
false
Answer Key & Detailed Explanations
Question 1
Correct Answer: A
Explanation
String objects are immutable.
The concat() method returns a new String, but the returned value is ignored.
s.concat("8");
does not modify s.
Output
Java
Interview Follow-up
How would the output change if StringBuilder were used instead?
Question 2
Correct Answer: B
Explanation
String s1 = "Java";
String s2 = "Java";
Both references point to the same object in the String Pool.
new String("Java")
always creates a new object on the heap.
Therefore
s1 == s2 → true
s1 == s3 → false
Interview Follow-up
- Difference between
==andequals() - What does
intern()do?
Question 3
Correct Answer: A
Explanation
list.get(0) returns a String.
Assigning it to an Object reference is valid because String is a subclass of Object.
Output
Java
Interview Follow-up
Why is the following not allowed?
List<Object> list =
new ArrayList<String>();
(Expected answer: Generics are invariant.)
Question 4
Correct Answer: A
Explanation
Status.valueOf("NEW") performs an exact lookup using the enum constant name.
Output
NEW
If "new" were used instead, an IllegalArgumentException would be thrown because the lookup is case-sensitive.
Question 5
Correct Answer: A
Explanation
LocalDate is immutable.
LocalDate.of(2026,7,31)
plus five days becomes
2026-08-05
The API automatically handles month boundaries.
Question 6
Correct Answer: A
Explanation
The subquery
SELECT MAX(SALARY)
FROM EMPLOYEE
returns
8000
The outer query returns the employee whose salary is 8000.
Output
Tom
Question 7 – Sample Solution
Traditional
String input = "programming";
Set<Character> seen = new LinkedHashSet<>();
for(char c : input.toCharArray()){
seen.add(c);
}
StringBuilder sb = new StringBuilder();
for(char c : seen){
sb.append(c);
}
System.out.println(sb);
Java 8
String result =
input.chars()
.distinct()
.collect(StringBuilder::new,
StringBuilder::appendCodePoint,
StringBuilder::append)
.toString();
Complexity
Time: O(n)
Space: O(n)
Question 8 – Sample Solution
map.entrySet()
.stream()
.sorted(Map.Entry
.<String,Integer>comparingByValue()
.reversed())
.forEach(System.out::println);
Concepts Tested
- Streams
- EntrySet
- Comparator
- Method References
- Sorting
Question 9 – Sample Solution
String s1 = "ABCD";
String s2 = "CDAB";
boolean result =
s1.length() == s2.length()
&& (s1 + s1).contains(s2);
System.out.println(result);
Explanation
A rotation of a string will always be a substring of the original string concatenated with itself.
Example
ABCDABCD
contains
CDAB
Complexity
Time: O(n)
Space: O(n)
Evaluation Guide
| Score | Recommendation |
|---|---|
| 9/9 | Excellent – Strong Java Backend Developer |
| 7–8 | Good – Recommended for Technical Round |
| 5–6 | Average – Needs Deeper Evaluation |
| Below 5 | Not Recommended |
Interviewer’s Notes
This set evaluates concepts that frequently appear in production code:
- String immutability and the String Pool
==vsequals()- Generic type safety and invariance
- Enum behavior and
valueOf() - Java 8 Date/Time API immutability
- Aggregate SQL functions
- Ordered duplicate removal
- Sorting Maps with Streams
- Rotation detection algorithms
For strong candidates, ask follow-up questions about why these APIs behave as they do, discuss alternative implementations, and ask for the time and space complexity of the programming solutions.
