20 Tricky Java Output Questions Every Experienced Developer Should Know

Java interviews often contain tricky output-based questions that test your understanding of core Java concepts rather than your ability to memorize syntax.

These questions typically cover String Pool, Wrapper Classes, Method Overloading, Inheritance, Exception Handling, finally blocks, Increment Operators and Java Memory concepts.

Let's challenge your Java knowledge with 20 popular interview questions.

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Question 1

String s1 = "Java";
String s2 = "Java";

System.out.println(s1 == s2);

Output

true

Explanation

String literals are stored in the String Pool. Both variables point to the same memory location.

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Question 2

String s1 = new String("Java");
String s2 = new String("Java");

System.out.println(s1 == s2);

Output

false

Explanation

Two separate objects are created in heap memory. Therefore reference comparison returns false.

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Question 3

String s1 = new String("Java");
String s2 = new String("Java");

System.out.println(s1.equals(s2));

Output

true

equals() compares content, not memory references.

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Question 4

Integer a = 127;
Integer b = 127;

System.out.println(a == b);

Output

true

Explanation

Integer values from -128 to 127 are cached by Java. Both references point to the same cached object.

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Question 5

Integer a = 128;
Integer b = 128;

System.out.println(a == b);

Output

false

Explanation

128 falls outside Integer Cache range. Separate objects are created.

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Question 6

String str = null;

System.out.println(str instanceof String);

Output

false

Explanation

instanceof never throws NullPointerException. It simply returns false.

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Question 7

System.out.println(10 + 20 + "Java");

Output

30Java

Addition occurs before String concatenation.

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Question 8

System.out.println("Java" + 10 + 20);

Output

Java1020

Once a String appears, subsequent operations become concatenations.

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Question 9

int x = 10;

System.out.println(x++ + ++x);

Output

22

Explanation

x++ returns 10 then x becomes 11. ++x makes x 12 and returns 12. Result = 10 + 12.

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Question 10

int x = 5;

System.out.println(x+++x);

Output

11

Explanation

Compiler interprets this as:

x++ + x

Result becomes 5 + 6.

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Question 11

try {
    return;
}
finally {
    System.out.println("Finally");
}

Output

Finally

finally block executes before method exits.

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Question 12

try {
    System.exit(0);
}
finally {
    System.out.println("Finally");
}

Output

No Output

JVM terminates immediately.

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Question 13

StringBuilder sb =
        new StringBuilder("Java");

sb.append(" 8");

System.out.println(sb);

Output

Java 8

StringBuilder is mutable.

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Question 14

final StringBuilder sb =
        new StringBuilder("Java");

sb.append(" 21");

System.out.println(sb);

Output

Java 21

Explanation

final prevents reference reassignment, not object modification.

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Question 15

String s = "Java";

s.concat(" 8");

System.out.println(s);

Output

Java

String objects are immutable. concat() returns a new String.

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Question 16

System.out.println(Math.round(2.5));
System.out.println(Math.round(3.5));

Output

3
4

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Question 17

String s = null;

System.out.println(String.valueOf(s));

Output

null

String.valueOf() safely handles null references.

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Question 18

List<String> list =
        Arrays.asList("Java","Spring");

list.add("Kafka");

Output

UnsupportedOperationException

Explanation

Arrays.asList() returns a fixed-size list.

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Question 19

String s = "Java";

System.out.println(s.charAt(4));

Output

StringIndexOutOfBoundsException

Valid indexes are 0 to 3.

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Question 20

String s1 = "Ja" + "va";
String s2 = "Java";

System.out.println(s1 == s2);

Output

true

Explanation

Compiler performs String constant folding and uses the String Pool.

Most Common Topics Covered

• String Pool
• Wrapper Classes
• Integer Cache
• StringBuilder
• Exception Handling
• finally Block
• instanceof Operator
• Collection Framework
• Immutability
• Operators

Interview Tips

• Never assume == compares content.
• Know Integer cache behaviour.
• Understand String Pool concepts.
• Remember finally block execution rules.
• Practice output-based questions regularly.
• Focus on Java memory concepts and object references.

Conclusion

Output-based Java questions reveal how well a developer understands JVM behavior, String Pool, Collections, Wrapper Classes and Exception Handling. Mastering these questions can significantly improve interview performance for both mid-level and senior Java developers.

Keywords

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