Top 40+ String in Java Interview Questions with Answers 2026

Strings are one of the most heavily tested topics in Java interviews. Here are commonly asked String-related questions along with clear answers.

1. Why is String immutable in Java?

Once a String object is created, its value cannot be changed. This makes Strings safe to share across threads, safe to use as HashMap keys, and enables the JVM to optimize memory using the String pool.

2. What is the String pool?

The String pool is a special memory area in the heap where Java stores string literals, allowing identical string values to be reused instead of creating duplicate objects.

3. Difference between String, StringBuilder, and StringBuffer?

String is immutable. StringBuilder is mutable and not thread-safe, making it faster for single-threaded use. StringBuffer is mutable and thread-safe due to synchronized methods.

4. How do you compare two Strings in Java?

String a = "hello";
String b = new String("hello");
System.out.println(a == b);         // false, compares references
System.out.println(a.equals(b));    // true, compares content

5. How do you reverse a String in Java?

String str = "hello";
String reversed = new StringBuilder(str).reverse().toString();

6. How do you check if a String is a palindrome?

String str = "madam";
String reversed = new StringBuilder(str).reverse().toString();
boolean isPalindrome = str.equals(reversed);

7. What does the intern() method do?

It returns a reference to the string from the String pool, adding it to the pool if it isn't already present.

8. How do you count occurrences of a character in a String?

String str = "banana";
long count = str.chars().filter(c -> c == 'a').count();

9. What is the difference between == and equals() for Strings?

== compares object references, while equals() compares the actual character content of the strings.

10. How do you split a String in Java?

String csv = "a,b,c";
String[] parts = csv.split(",");

11. What is a StringTokenizer?

An older utility class used to break a string into tokens based on delimiters; split() and regex-based approaches are generally preferred now.

12. How do you check if two Strings are anagrams?

char[] a = "listen".toCharArray();
char[] b = "silent".toCharArray();
Arrays.sort(a);
Arrays.sort(b);
boolean isAnagram = Arrays.equals(a, b);