Why are output-based questions asked in Java interviews?

Output-based questions test whether you truly understand Java's behavior — variable scoping, type promotion, autoboxing, static vs instance context, and more. They reveal gaps that syntax knowledge alone cannot.

What is the difference between a compilation error and a runtime exception?

Compilation errors are caught by the compiler before the program runs — like uninitialized local variables or type mismatches. Runtime exceptions occur while the program executes — like NullPointerException from unboxing null.

Why does byte + byte return int in Java?

Java promotes smaller types (byte, short, char) to int during arithmetic operations. This is called integer promotion. To store the result in a byte, an explicit cast is required.

What is autoboxing and unboxing in Java?

Autoboxing is automatic conversion of a primitive (int) to its wrapper (Integer). Unboxing is the reverse. Unboxing a null wrapper causes a NullPointerException at runtime.

What are number literal prefixes in Java?

0x means hexadecimal (base 16), 0b means binary (base 2), a leading 0 means octal (base 8), and underscores (_) are allowed as visual separators in numeric literals.

50 Java Output-Based Interview Questions with Answers | Core Java Tricky Programs

50 Java Output-Based Interview Questions with Answers

Welcome to one of the most important interview prep posts you'll ever read! 🎯

Output-based questions are the secret weapon of Java interviews. They don't just test whether you memorized syntax — they test whether you truly understand how Java works under the hood.

These 50 questions cover variables, data types, operators, type casting, static blocks, instance initializers, bitwise operations, and more. Every question here has appeared in real interviews at companies like TCS, Infosys, Wipro, Amazon, and product-based startups.

How to use this post: Read each question, guess the output in your head, then click "Show Answer" to check. Don't run the code first — that's cheating! 😄

💡 Important: Pay close attention to the difference between compilation errors, runtime exceptions, and actual outputs. Most interviewers love this trap!

Questions 1–11: Static vs Instance Context

Question 1

What is the output of the below program?

public class First {
    int i;
    public static void main(String[] args) {
        System.out.println(i);
    }
}

✅ Show Answer

Compilation Error. You cannot make a static reference to the non-static field i. Since main is static, it can't access instance variables directly.

💡 Interview Tip: Interviewers love this one — it tests if you understand the difference between static and instance context.

Question 2

What is the output?

public class First {
    int i;
    public static void main(String[] args) {
        int i;
        System.out.println(i);
    }
}

✅ Show Answer

Compilation Error. Variable i might not have been initialized. Local variables must be assigned before use — Java doesn't give default values to local variables.

Question 3

What is the output?

public class First {
    int i;
    static int i;
    public static void main(String[] args) {
        System.out.println(i);
    }
}

✅ Show Answer

Compilation Error. Duplicate field i. You cannot declare two variables with the same name in the same class — even if one is static and one is instance.

Question 4

What is the output?

public class First {
    int i = 100;
    static int j = i;
    public static void main(String[] args) {
        System.out.println(j);
    }
}

✅ Show Answer

Compilation Error. Cannot make a static reference to the non-static field i. Static variables cannot use instance variables in their initializer.

Question 5

What is the output?

public class First {
    int i = 100;
    static int j = 10;
    public static void main(String[] args) {
        int k = i + j;
        System.out.println(k);
    }
}

✅ Show Answer

Compilation Error. Cannot make a static reference to non-static field i from main (static context). Only j can be accessed directly here.

Question 6

What is the output?

public class First {
    public static void main(String[] args) {
        int i;
        System.out.println(i);
    }
}

✅ Show Answer

Compilation Error. Variable i might not have been initialized.

💡 Key Rule: Class-level variables get default values, but local variables do NOT.

Question 7

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 10, k;
        System.out.println(k);
    }
}

✅ Show Answer

Compilation Error. Variable k might not have been initialized. Declaring without assignment means it has no value.

Question 8

What is the output?

public class First {
    public static void main(String[] args) {
        int i, k = 10;
        System.out.println(i);
    }
}

✅ Show Answer

Compilation Error. Variable i might not have been initialized. Only k was assigned 10.

Question 9

What is the output?

public class First {
    static {
        System.out.println(i);
    }
    static int i = 109;
    public static void main(String[] args) {
    }
}

✅ Show Answer

Compilation Error. Cannot reference a field before it is defined — this is called an illegal forward reference.

💡 Why: Static blocks run in the order they appear. Since i is declared AFTER the static block, it doesn't exist yet when the block runs.

Question 10

What is the output?

public class First {
    int i = 10;
    static {
        System.out.println(i);
    }
    public static void main(String[] args) {
    }
}

✅ Show Answer

Compilation Error. Cannot make a static reference to the non-static field i. Static blocks cannot access instance variables.

Question 11

What is the output?

public class First {
    {
        System.out.println(i);
    }
    public static void main(String[] args) {
    }
    int i = 10;
}

✅ Show Answer

Compilation Error. Illegal forward reference. Instance initializer block cannot reference i before its declaration.

Questions 12–18: Increment & Type Promotion

Question 12

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 10;
        System.out.println(i++);
    }
}

✅ Show Answer

Output: 10

Post-increment: the original value (10) is returned first, then i becomes 11. But since we're printing the returned value, it prints 10.

Question 13

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 10;
        System.out.println(++i);
    }
}

✅ Show Answer

Output: 11

Pre-increment: i becomes 11 first, then the value is returned.

Question 14

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 10;
        System.out.println(++i + i++);
    }
}

✅ Show Answer

Output: 22

Step by step:

++i → i becomes 11, returns 11
i++ → returns 11, then i becomes 12
11 + 11 = 22

💡 Interview Tip: This is a favorite! Track each increment carefully.

Question 15

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 10;
        System.out.println(++i + "i++");
    }
}

✅ Show Answer

Output: 11i++

First ++i makes i = 11, then it's concatenated with the string "i++". Java concatenates when any operand is a String.

Question 16

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 1;
        char c = 1;
        System.out.println(i + c);
    }
}

✅ Show Answer

Output: 2

char is promoted to int (its ASCII/Unicode value). So 1 + 1 = 2.

Question 17

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 1;
        char c = 1 + 1;
        System.out.println(i + c);
    }
}

✅ Show Answer

Output: 3

char c = 1 + 1 is allowed because both operands are compile-time constants. c = 2. Then 1 + 2 = 3.

Question 18

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 1;
        char c = 1 + i;
        System.out.println(i + c);
    }
}

✅ Show Answer

Compilation Error. Cannot assign int to char without explicit cast. Since i is a variable, the expression is not a compile-time constant.

Fix: char c = (char)(1 + i);

Questions 19–24: byte, char & short Arithmetic

Question 19

What is the output?

public class First {
    public static void main(String[] args) {
        byte a = 1;
        byte b = 1;
        byte c = a + b;
        System.out.println(c);
    }
}

✅ Show Answer

Compilation Error. byte + byte results in int due to integer promotion. Requires explicit cast.

Fix: byte c = (byte)(a + b);

Question 20

What is the output?

public class First {
    public static void main(String[] args) {
        byte a = 1;
        byte b = 1;
        byte c = (byte)a + (byte)b;
        System.out.println(c);
    }
}

✅ Show Answer

Compilation Error. Casting each operand separately doesn't help — the result of addition is still promoted to int.

Fix: Cast the whole expression: byte c = (byte)(a + b);

Question 21

What is the output?

public class First {
    public static void main(String[] args) {
        byte a = 1;
        byte b = 1;
        byte c = (byte)(a + b);
        System.out.println(c);
    }
}

✅ Show Answer

Output: 2

The cast applies to the whole result — so int 2 becomes byte 2. Works perfectly.

Question 22

What is the output?

public class First {
    public static void main(String[] args) {
        byte a = 1;
        byte b = 1;
        short c = a + b;
        System.out.println(c);
    }
}

✅ Show Answer

Compilation Error. byte + byte = int. Cannot assign int to short without explicit cast.

Question 23

What is the output?

public class First {
    public static void main(String[] args) {
        byte a = 1;
        char b = 1;
        short c = a + b;
        System.out.println(c);
    }
}

✅ Show Answer

Compilation Error. byte + char = int. Cannot assign int to short without cast.

Question 24

What is the output?

public class First {
    public static void main(String[] args) {
        char a = 'a';
        char b = 'b';
        int k = a + b;
        System.out.println(k);
    }
}

✅ Show Answer

Output: 195

'a' = 97, 'b' = 98. So 97 + 98 = 195.

💡 Remember: 'a' = 97, 'A' = 65, '0' = 48 in ASCII.

Questions 25–32: Wrapper Classes & Autoboxing

Question 25

What is the output?

public class First {
    static float i = 10.0;
    public static void main(String[] args) {
        System.out.println(f);
    }
}

✅ Show Answer

Compilation Error. Two issues:

10.0 is a double literal — cannot assign to float without f suffix.
Variable f is never declared. Should be i.

Question 26

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 10;
        Float b = i;
        System.out.println(b);
    }
}

✅ Show Answer

Compilation Error. Cannot convert int to Float (wrapper class) without autoboxing or cast.

Fix: Float b = (float) i; or float b = i;

Question 27

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 10;
        Long b = i;
        System.out.println(b);
    }
}

✅ Show Answer

Compilation Error. Cannot convert int to Long directly. int → long works, but int → Long (wrapper) needs cast.

Fix: Long b = (long) i;

Question 28

What is the output?

public class First {
    public static void main(String[] args) {
        Long i = 10;
        System.out.println(i);
    }
}

✅ Show Answer

Compilation Error. 10 is an int literal. Cannot assign int to Long directly.

Fix: Long i = 10L;

Question 29

What is the output?

public class First {
    public static void main(String[] args) {
        Double i = 10.9f;
        System.out.println(i);
    }
}

✅ Show Answer

Compilation Error. Cannot assign float to Double (wrapper class).

Fix: Double i = 10.9; or double i = 10.9f;

Question 30

What is the output?

public class First {
    public static void main(String[] args) {
        Integer i = null;
        int k = i;
        System.out.println(k);
    }
}

✅ Show Answer

Runtime Exception: NullPointerException

Unboxing a null Integer to int throws NPE at runtime — compiles fine!

💡 Interview Tip: This is a classic autoboxing trap.

Question 31

What is the output?

public class First {
    static int i;
    static Integer j;
    public static void main(String[] args) {
        System.out.println(i + j);
    }
}

✅ Show Answer

Runtime Exception: NullPointerException

i is 0 (default), but j is null. Unboxing j for addition throws NPE.

Question 32

What is the output?

public class First {
    static int i = 10;
    static {
        i++;
    }
    {
        i++;
    }
    First() {
        i++;
    }
    static void get() {
        i++;
    }
    public static void main(String[] args) {
        new First();
        System.out.println(i);
    }
}

✅ Show Answer

Output: 13

Step-by-step trace:

Static variable init: i = 10
Static block runs: i = 11
main() starts
new First() triggers:
- Instance initializer block: i = 12
- Constructor: i = 13
Print i → 13

💡 Explanation: This tests your knowledge of initialization order — static → instance → constructor.

Questions 33–40: Number Literals

Question 33

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 1010;
        System.out.println(i);
    }
}

✅ Show Answer

Output: 1010

Decimal literal. Just a normal number.

Question 34

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 0101;
        System.out.println(i);
    }
}

✅ Show Answer

Output: 65

Leading 0 means octal (base 8). 0101 in octal = 1×64 + 0×8 + 1 = 65.

Question 35

What is the output?

public class First {
    public static void main(String[] args) {
        char c = 0101;
        System.out.println(c);
    }
}

✅ Show Answer

Output: A

0101 octal = 65 decimal. ASCII 65 = 'A'.

Question 36

What is the output?

public class First {
    public static void main(String[] args) {
        char a = 0101;
        char b = 101;
        char c = a + b;
        System.out.println(c);
    }
}

✅ Show Answer

Compilation Error. char + char = int. Cannot assign to char without cast.

Fix: char c = (char)(a + b); (would output char with ASCII 65+101=166)

Question 37

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 5_6;
        System.out.println(i);
    }
}

✅ Show Answer

Output: 56

Underscores in numeric literals are ignored by the compiler (Java 7+). Helps readability.

Question 38

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 0x1a;
        System.out.println(i);
    }
}

✅ Show Answer

Output: 26

0x prefix means hexadecimal. 0x1a = 1×16 + 10 = 26.

Question 39

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 0b11010;
        System.out.println(i);
    }
}

✅ Show Answer

Output: 26

0b prefix means binary. 11010 = 16+8+2 = 26.

Question 40

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 0x5a;
        int k = 10;
        System.out.println(i + k);
    }
}

✅ Show Answer

Output: 100

0x5a = 90 decimal. 90 + 10 = 100.

Questions 41–44: Bitwise Operators

Question 41

What is the output?

public class First {
    public static void main(String[] args) {
        System.out.println(9 | 8);
    }
}

✅ Show Answer

Output: 9

Bitwise OR: 9 = 1001, 8 = 1000. OR = 1001 = 9.

Question 42

What is the output?

public class First {
    public static void main(String[] args) {
        System.out.println(9 & 8);
    }
}

✅ Show Answer

Output: 8

Bitwise AND: 9 = 1001, 8 = 1000. AND = 1000 = 8.

Question 43

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 19;
        i = i >> 2;
        System.out.println(i);
    }
}

✅ Show Answer

Output: 4

Right shift by 2 = divide by 4. 19 / 4 = 4 (integer division).

Question 44

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 19;
        i = i << 2;
        System.out.println(i);
    }
}

✅ Show Answer

Output: 76

Left shift by 2 = multiply by 4. 19 × 4 = 76.

Questions 45–50: Equality & Reference Comparison

Question 45

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 10;
        char j = 10;
        System.out.println(i == j);
    }
}

✅ Show Answer

Output: true

char is promoted to int for comparison. 10 == 10 → true.

Question 46

What is the output?

public class First {
    public static void main(String[] args) {
        int i = 97;
        char j = 'a';
        System.out.println(i == j);
    }
}

✅ Show Answer

Output: true

'a' = 97 in ASCII. 97 == 97 → true.

Question 47

What is the output?

public class First {
    public static void main(String[] args) {
        int i = (Integer)null;
        char j = 'a';
        System.out.println(i == j);
    }
}

✅ Show Answer

Runtime Exception: NullPointerException

Casting null to Integer and then auto-unboxing to int causes NPE at runtime.

Question 48

What is the output?

public class First {
    public static void main(String[] args) {
        Integer i = null;
        char j = 'a';
        System.out.println(i == j);
    }
}

✅ Show Answer

Output: false

No NPE here! i is Integer (object), j is char (primitive). Java unboxes i to compare, but since i is null and j is a primitive, it uses reference comparison — null != anything → false.

💡 Tricky: This compiles and runs — no exception! Because the comparison doesn't force unboxing when types differ.

Question 49

What is the output?

public class First {
    public static void main(String[] args) {
        Integer i = null;
        Character j = 'a';
        System.out.println(i == j);
    }
}

✅ Show Answer

Output: false

Both are objects (wrapper types). Reference comparison. null != any object → false.

Question 50

What is the output?

public class First {
    public static void main(String[] args) {
        Integer i = 97;
        Character j = 'a';
        System.out.println(i + j);
    }
}

✅ Show Answer

Output: 194

Both are unboxed to int for addition. i = 97, j = 97 (ASCII 'a'). 97 + 97 = 194.

Final Thoughts

Congratulations on completing all 50 questions! 🎉

If you got most of them right, you're well on your way to cracking Java interviews. If some caught you off guard, don't worry — that's exactly why output-based questions are so valuable. They reveal gaps in your understanding that syntax alone can't fix.

🔑 Key Takeaways from This Post

Static vs Instance: Static methods can't access instance variables directly.
Default Values: Class fields get defaults (0, null, false), local variables don't.
Integer Promotion: byte + byte = int, char + char = int.
Type Casting: Widening is automatic, narrowing needs explicit cast.
Autoboxing/Unboxing: Watch out for NullPointerException on null wrappers.
Number Literals: 0x = hex, 0b = binary, 0 = octal, _ = separator.
Bitwise Operators: &, |, <<, >> work on binary representations.

📚 Practice More

Try to modify these programs and predict new outputs. The more you practice, the sharper your Java intuition becomes.

Want the next level? Check out:

Java 8 Stream API interview questions
Java collections output-based questions
Multithreading tricky programs
Exception handling output questions

If this post helped you, share it with a friend preparing for interviews!

Pages

Java Data Type Questions

Questions 1–11: Static vs Instance Context

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11

Questions 12–18: Increment & Type Promotion

Question 12

Question 13

Question 14

Question 15

Question 16

Question 17

Question 18

Questions 19–24: byte, char & short Arithmetic

Question 19

Question 20

Question 21

Question 22

Question 23

Question 24

Questions 25–32: Wrapper Classes & Autoboxing

Question 25

Question 26

Question 27

Question 28

Question 29

Question 30

Question 31

Question 32

Questions 33–40: Number Literals

Question 33

Question 34

Question 35

Question 36

Question 37

Question 38

Question 39

Question 40

Questions 41–44: Bitwise Operators

Question 41

Question 42

Question 43

Question 44

Questions 45–50: Equality & Reference Comparison

Question 45

Question 46

Question 47

Question 48

Question 49

Question 50

Final Thoughts

🔑 Key Takeaways from This Post

📚 Practice More

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