Five Java String Interview Questions with Answers and Memory Analysis

The article presents five common Java String interview questions, explains the expected output, and provides detailed analysis of string equality, object creation, and memory behavior.

Question 1: Determine whether two literals st1 and st2 are equal using == and equals.

package string;
public class Demo2_String {
    public static void main(String[] args) {
        String st1 = "abc";
        String st2 = "abc";
        System.out.println(st1 == st2);
        System.out.println(st1.equals(st2));
    }
}

Output:

true

true

Explanation: literals share the same object in the string pool, so == returns true; equals compares content and also returns true.

Question 2: How many objects are created by new String("abc")? String st1 = new String("abc"); Answer: two objects – one in the heap and one in the string pool (the pool object is copied into the heap object).

Question 3: Compare a new String("abc") with a literal "abc".

String st1 = new String("abc");
String st2 = "abc";
System.out.println(st1 == st2);
System.out.println(st1.equals(st2));

Output:

false

true

Explanation: new creates a distinct heap object, so reference comparison fails; content comparison succeeds.

Question 4: Compare concatenated literals "a" + "b" + "c" with literal "abc".

String st1 = "a" + "b" + "c";
String st2 = "abc";
System.out.println(st1 == st2);
System.out.println(st1.equals(st2));

Output:

true

true

Explanation: The compiler folds the concatenation at compile time, producing the same pool object.

Question 5: Compare runtime concatenation "ab" + "c" with literal "abc".

String st1 = "ab";
String st2 = "abc";
String st3 = st1 + "c";
System.out.println(st2 == st3);
System.out.println(st2.equals(st3));

Output:

false

true

Explanation: The + operation creates a new StringBuilder at runtime, producing a new heap object; thus reference comparison fails while content comparison succeeds.

Conclusion: Mastering the Java string pool, the difference between == and equals, and compiler optimizations for constant strings is essential for Java interview preparation.