Performance testing interviews often include programming questions to validate that you can script, automate, and debug under real-world scenarios.
This guide compiles 50 common questions with answers — covering strings, arrays, algorithms, file handling, JSON/XML, random data, and concurrency — in Java, Groovy (JMeter), and C (LoadRunner).
Use this as a refresher before interviews.
📌 Section 1: Strings (Q1–Q10)
Q1. Reverse a String
Java
String str = "performance";
String rev = new StringBuilder(str).reverse().toString();
System.out.println(rev);
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Groovy
groovy
def str = "performance"
println str.reverse()
C
c
char str[] = "performance";
int i, len = strlen(str);
for(i=len-1; i>=0; i--) printf("%c", str[i]);
Q2. Check Palindrome
java
String str="madam";
System.out.println(str.equals(new StringBuilder(str).reverse().toString()));
groovy
def str="madam"
println str == str.reverse()
c
char str[]="madam"; int i=0, j=strlen(str)-1, flag=1;
while(i<j) if(str[i++]!=str[j--]) flag=0;
printf(flag?"Palindrome":"Not Palindrome");
Q3. Find Substring
java
System.out.println("hello".contains("ell"));
groovy
println "hello".contains("ell")
c
printf(strstr("hello","ell")?"Found":"Not Found");
Q4. Count Vowels
java
String s="performance"; long count=s.chars().filter(c->"aeiou".indexOf(c)!=-1).count();
System.out.println(count);
groovy
println "performance".count{ it in ['a','e','i','o','u'] }
c
char s[]="performance"; int c=0;
for(int i=0;i<strlen(s);i++) if(strchr("aeiou",s[i])) c++;
printf("%d",c);
Q5. Remove Whitespace
java
System.out.println("a b c".replaceAll("\\s",""));
groovy
println "a b c".replaceAll("\\s","")
c
// copy only non-space chars
Q6. Find Duplicate Characters
java
String s="testing";
Map<Character,Integer> map=new HashMap<>();
for(char c:s.toCharArray()) map.put(c,map.getOrDefault(c,0)+1);
map.forEach((k,v)->{if(v>1)System.out.println(k);});
Q7. String Compression
Input: aaabbc → Output: a3b2c1
java
String s="aaabbc"; StringBuilder sb=new StringBuilder();
for(int i=0;i<s.length();) {
int j=i; while(j<s.length() && s.charAt(i)==s.charAt(j)) j++;
sb.append(s.charAt(i)).append(j-i); i=j;
}
System.out.println(sb);
Q8. Anagram Check
java
char[] a="listen".toCharArray(), b="silent".toCharArray();
Arrays.sort(a); Arrays.sort(b);
System.out.println(Arrays.equals(a,b));
Q9. Extract Tokens from URL
java
String url="https://site.com?id=123&user=john";
String[] parts=url.split("\\?");
System.out.println(parts[1]); // id=123&user=john
Q10. Replace Words
java
System.out.println("LoadRunner vs JMeter".replace("vs","and"));
📌 Section 2: Arrays & Collections (Q11–Q20)
Q11. Find Duplicates
java
int[] arr={1,2,3,2,1};
Set<Integer> set=new HashSet<>();
for(int n:arr) if(!set.add(n)) System.out.println("Dup:"+n);
Q12. Find Missing Number (1..N)
java
int[] arr={1,2,4,5}; int n=5, sum=n*(n+1)/2, s=0;
for(int x:arr) s+=x;
System.out.println("Missing:"+(sum-s));
Q13. Max/Min
java
int[] arr={3,5,1};
System.out.println(Arrays.stream(arr).max().getAsInt());
Q14. Reverse an Array
java
int[] arr={1,2,3};
for(int i=0,j=arr.length-1;i<j;i++,j--){
int tmp=arr[i]; arr[i]=arr[j]; arr[j]=tmp;
}
Q15. Rotate Array
java
Collections.rotate(Arrays.asList(arr),2);
Q16. Check Sorted
java
boolean sorted=IntStream.range(1,arr.length).allMatch(i->arr[i]>=arr[i-1]);
Q17. Common Elements
java
Set<Integer> s1=new HashSet<>(Arrays.asList(1,2,3));
Set<Integer> s2=new HashSet<>(Arrays.asList(2,3,4));
s1.retainAll(s2);
System.out.println(s1);
Q18. Merge Two Sorted Arrays
java
// classic merge procedure
Q19. Remove Duplicates
java
Arrays.stream(arr).distinct().toArray();
Q20. Frequency Count
java
Map<Integer,Long> freq=Arrays.stream(arr).boxed()
.collect(Collectors.groupingBy(i->i,Collectors.counting()));
📌 Section 3: Numbers & Algorithms (Q21–Q30)
Q21. Fibonacci
java
int a=0,b=1;
for(int i=0;i<10;i++){System.out.print(a+" "); int c=a+b; a=b;b=c;}
Q22. Factorial
java
int f=1,n=5;
for(int i=1;i<=n;i++) f*=i;
Q23. Prime Check
java
int n=17; boolean prime=IntStream.range(2,n).noneMatch(i->n%i==0);
Q24. Armstrong Number
java
int n=153,sum=0,t=n;
while(t>0){int d=t%10; sum+=d*d*d; t/=10;}
System.out.println(sum==n);
Q25. Sum of Digits
java
int n=1234,sum=0;
while(n>0){sum+=n%10;n/=10;}
Q26. Swap Numbers (No Temp)
java
a=a+b; b=a-b; a=a-b;
Q27. GCD
java
int gcd(int a,int b){return b==0?a:gcd(b,a%b);}
Q28. Binary Search
java
int bs(int arr[],int x){
int l=0,h=arr.length-1;
while(l<=h){int m=(l+h)/2;
if(arr[m]==x)return m;
if(arr[m]<x) l=m+1; else h=m-1;}
return -1;
}
Q29. Bubble Sort
java
for(int i=0;i<n-1;i++)for(int j=0;j<n-i-1;j++)
if(arr[j]>arr[j+1]){int t=arr[j];arr[j]=arr[j+1];arr[j+1]=t;}
Q30. Quick Sort
java
// standard partition-based algorithm
📌 Section 4: Data Structures (Q31–Q35)
Q31. Stack
java
Stack<Integer> st=new Stack<>();
st.push(1); st.pop();
Q32. Queue
java
Queue<Integer> q=new LinkedList<>();
q.add(1); q.remove();
Q33. Reverse Linked List
java
// iterative reversal
Q34. Word Count
java
String s="this is test this";
Map<String,Long> map=Arrays.stream(s.split(" "))
.collect(Collectors.groupingBy(w->w,Collectors.counting()));
Q35. Balanced Parentheses
java
// use stack to check if '(' matches ')'
📌 Section 5: File Handling (Q36–Q40)
Q36. Read File
java
Files.lines(Paths.get("file.txt")).forEach(System.out::println);
Q37. Write File
java
Files.write(Paths.get("out.txt"), "hello".getBytes());
Q38. Count Lines
java
long lines=Files.lines(Paths.get("file.txt")).count();
Q39. Search Keyword
java
Files.lines(Paths.get("file.txt")).filter(l->l.contains("error")).forEach(System.out::println);
Q40. Parse CSV
java
Files.lines(Paths.get("data.csv")).map(l->l.split(",")).forEach(arr->System.out.println(arr[0]));
📌 Section 6: JSON & XML (Q41–Q45)
Q41. Parse JSON
java
import org.json.*;
JSONObject obj=new JSONObject("{\"user\":\"john\",\"token\":\"xyz\"}");
System.out.println(obj.getString("token"));
Q42. Convert Object to JSON
java
JSONObject obj=new JSONObject();
obj.put("id",123); obj.put("name","test");
Q43. Parse XML
java
Document doc=DocumentBuilderFactory.newInstance().newDocumentBuilder().parse("file.xml");
Q44. Count XML Nodes
java
NodeList list=doc.getElementsByTagName("user");
System.out.println(list.getLength());
Q45. Validate JSON Contains Key
java
System.out.println(obj.has("token"));
📌 Section 7: Random Data (Q46–Q48)
Q46. Random Number
java
int n=new Random().nextInt(100);
Q47. UUID
java
String id=UUID.randomUUID().toString();
Q48. Shuffle
java
List<Integer> list=Arrays.asList(1,2,3,4,5);
Collections.shuffle(list);
📌 Section 8: Concurrency (Q49–Q50)
Q49. Threads
java
for(int i=0;i<5;i++){
new Thread(()->System.out.println("Hello "+Thread.currentThread().getId())).start();
}
Q50. Synchronization
java
class Counter{int c=0; synchronized void inc(){c++;}}
Counter ct=new Counter();
✅ Final Takeaway
Performance testers/engineers don’t need to be full-time developers — but being comfortable with strings, arrays, file I/O, JSON/XML parsing, and multithreading basics makes you stand out.
These 50 questions cover the most common interview checks across JMeter, LoadRunner, and real-world scripting.
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