Tricky Java Questions (Pattern Based)(10th class)

 

Tricky Java Questions (Pattern Based)

1(i)
What will be the output of the following code?

System.out.println(10 + 20 + "Java" + 30 + 40);

a) 3030Java
b) 30Java3040
c) 30Java70
d) Java3040

✅ Answer: b) 30Java3040
📘 Topic: Operators + String Concatenation
💡 Reason: 10+20=30 (int addition), then "Java" makes the rest concatenation → 30Java3040.

1(ii)
Which of the following is a valid identifier in Java?
a) 1stValue
b) _result
c) new
d) a-b

✅ Answer: b) _result
📘 Topic: Identifiers & Keywords
💡 Reason: Identifiers can start with _ or letter, but not digits or operators. new is reserved keyword.

1(iii)
What will the following code print?

char ch = 'A';

System.out.println((int)(ch + 1));

a) 65
b) 66
c) A1
d) B

✅ Answer: b) 66
📘 Topic: Type Casting + ASCII
💡 Reason: 'A' = 65, so 65+1 = 66.

1(iv)
Which of the following statements about switch in Java is true?
a) switch can work with float
b) switch can work with String (since Java 7)
c) switch can check ranges like case >5:
d) switch can work only with boolean

✅ Answer: b) switch can work with String (since Java 7)
📘 Topic: Decision Making (switch)
💡 Reason: switch does not support float or ranges, and boolean is not allowed. String is allowed from Java 7.

1(v)
What is the result of:

System.out.println(15/4 + " " + 15.0/4);

a) 3 3.0
b) 3 3.75
c) 3.0 3.75
d) 3.75 3.75

✅ Answer: b) 3 3.75
📘 Topic: Integer Division & Floating Division
💡 Reason: 15/4 = 3 (integer division). 15.0/4 = 3.75.

1(vi)
Which Math function gives the smallest integer greater than or equal to -3.8?
a) Math.floor(-3.8)
b) Math.ceil(-3.8)
c) Math.round(-3.8)
d) Math.abs(-3.8)

✅ Answer: b) Math.ceil(-3.8)
📘 Topic: Math Class
💡 Reason: ceil moves up → nearest integer ≥ -3.8 is -3.

1(vii)
What will be the output of:

String s = "Hello";

System.out.println(s.substring(1,4));

a) Hel
b) Hell
c) ell
d) llo

✅ Answer: c) ell
📘 Topic: String Class Methods
💡 Reason: substring(start, end) includes start=1 (‘e’) but excludes end=4.

1(viii)
What is the value of x after executing:

int x = 5;

x += x++ + ++x;

a) 16
b) 17
c) 18
d) 19

✅ Answer: b) 17
📘 Topic: Operators (Increment + Assignment)
💡 Reason:

  • Initially x=5
  • x++ = 5 (then x=6)
  • ++x = 7 (x=7)
  • So x += 5+7 → 7+12=19 but since x=7 already, result = 17.

1(ix)
Which constructor call is valid for the following class?

class Test {

    Test(int a, double b) {}

}

a) new Test(10,20);
b) new Test(10.5,20);
c) new Test(10,20.5);
d) new Test();

✅ Answer: c) new Test(10,20.5);
📘 Topic: Constructors & Type Matching
💡 Reason: First parameter must be int, second must be double.

1(x)
Given:

int arr[][] = {{1,2,3},{4,5,6}};

System.out.println(arr[1][2]);

What will it print?
a) 2
b) 3
c) 5
d) 6

✅ Answer: d) 6
📘 Topic: 2D Arrays in Java
💡 Reason: arr[1] → second row {4,5,6}. Index 2 = 6.

✨ These are tricky but exam-friendly and strictly follow the pattern:

  • Question
  • Options
  • Answer
  • Reason
  • Topic

 

 

Super 👍 Let’s build a full Section A with 20 tricky MCQs in Java, exactly in the pattern we fixed:

SECTION A – (20 × 1 = 20 Marks)

1(i)
What will be the output?

System.out.println(5 + 5 + "5" + 5);

a) 1055
b) 555
c) 155
d) 55

✅ Answer: a) 1055
📘 Topic: String Concatenation & Operators
💡 5+5=10 then "5" → 105 then +5 → 1055.

1(ii)
Which of the following is not a valid keyword in Java?
a) goto
b) static
c) switch
d) include

✅ Answer: d) include
📘 Topic: Keywords in Java
💡 goto is reserved but unused, include belongs to C/C++.

1(iii)
The default value of an uninitialized boolean instance variable is:
a) true
b) false
c) 0
d) null

✅ Answer: b) false
📘 Topic: Data Types & Variables

1(iv)
Which of the following data types can store the largest value?
a) int
b) long
c) float
d) double

✅ Answer: d) double
📘 Topic: Data Types in Java

1(v)
What will be the output?

System.out.println(7/2*2.0);

a) 7.0
b) 6.0
c) 7
d) 6

✅ Answer: b) 6.0
📘 Topic: Type Casting & Division
💡 7/2=3 (int division), then 3*2.0 = 6.0.

1(vi)
Which of the following is true for switch?
a) Supports float case labels
b) Case labels must be unique
c) Default must always be last
d) Break is optional but mandatory

✅ Answer: b) Case labels must be unique
📘 Topic: Decision Making

1(vii)
What will be the output?

char c = 'B';

System.out.println((int)c);

a) 65
b) 66
c) 67
d) 68

✅ Answer: b) 66
📘 Topic: Characters & ASCII

1(viii)
Which method returns the length of a string?
a) size()
b) length
c) length()
d) getSize()

✅ Answer: c) length()
📘 Topic: String Class Methods

1(ix)
What is printed?

System.out.println("Hello".substring(1,4));

a) Hel
b) ell
c) llo
d) Hell

✅ Answer: b) ell
📘 Topic: Substring in Strings

1(x)
Which of the following loops will execute exactly once, even if the condition is false?
a) for loop
b) while loop
c) do…while loop
d) switch loop

✅ Answer: c) do…while loop
📘 Topic: Loops in Java

1(xi)
What is the output?

int x = 5;

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

a) 10
b) 11
c) 12
d) 13

✅ Answer: d) 13
📘 Topic: Increment Operators
💡 x++=5, then ++x=7, so 5+7=12. But after x=6, ++x=7, total 12? Wait check: x=5 → x++ =5, x=6 → ++x=7 → sum=12 ✅ Correction → Answer is c) 12.

1(xii)
What is the output of:

System.out.println(Math.floor(-2.1));

a) -2.0
b) -3.0
c) -1.0
d) 2.0

✅ Answer: b) -3.0
📘 Topic: Math Class Methods

1(xiii)
Which operator is used for bitwise AND in Java?
a) &&
b) &
c) |
d) ^

✅ Answer: b) &
📘 Topic: Operators (Bitwise)

1(xiv)
Which of these is a wrapper class in Java?
a) int
b) float
c) Integer
d) char

✅ Answer: c) Integer
📘 Topic: Wrapper Classes

1(xv)
What is the output?

int a = 2, b = 3;

System.out.println(Math.pow(a,b));

a) 6
b) 8.0
c) 9
d) 8

✅ Answer: b) 8.0
📘 Topic: Math Class – pow()

1(xvi)
Which exception occurs if you access an invalid array index?
a) NullPointerException
b) ArithmeticException
c) ArrayIndexOutOfBoundsException
d) NumberFormatException

✅ Answer: c) ArrayIndexOutOfBoundsException
📘 Topic: Exceptions in Java

1(xvii)
What is the output?

System.out.println("Java".compareTo("java"));

a) 0
b) Negative number
c) Positive number
d) Error

✅ Answer: b) Negative number
📘 Topic: String compareTo()
💡 Capital letters < small letters in Unicode.

1(xviii)
Which of the following is a valid constructor definition?
a) void Test() {}
b) Test() {}
c) public void Test() {}
d) int Test() {}

✅ Answer: b) Test() {}
📘 Topic: Constructors
💡 Constructors don’t have a return type.

1(xix)
Given:

int arr[][] = {{1,2,3},{4,5,6}};

System.out.println(arr[0][2]);

What is the output?
a) 1
b) 2
c) 3
d) 6

✅ Answer: c) 3
📘 Topic: 2D Arrays

1(xx)
Which loop will run exactly 5 times?
a) for(int i=1; i<=5; i++)
b) for(int i=0; i<5; i++)
c) Both a & b
d) while(true)

✅ Answer: c) Both a & b
📘 Topic: Loops in Java

 

Java – Question 2 (New Set)

2(i) Rewrite using single if statement

if(ch == 'y')

    System.out.println("YES");

else if(ch == 'Y')

    System.out.println("YES");

✅ Answer:

if(ch == 'y' || ch == 'Y')

    System.out.println("YES");

Explanation: Used logical OR (||) to combine both conditions.

2(ii) Expression Evaluation
Evaluate when a=5, b=2:

a+= ++b + a-- - b++;

System.out.println("a= " + a);

System.out.println("b= " + b);

✅ Answer:

  • Step 1: a = 5, b = 2
  • Expression: a = a + (++b + a-- - b++)
  • ++b = 3, so a = 5 + (3 + 5 - 3)
  • a-- = 5 (then a = 4), b++ = 3 (then b = 4)
  • So a = 5 + 5 = 10
  • Final values → a = 10, b = 4

2(iii) Error Identification

float x = 3.4;

switch(x) {

   case 3: System.out.println("Three"); break;

   case 4: System.out.println("Four");

}

✅ Answer:
Error → switch does not allow float.

Corrected Code:

int x = 3;

switch(x) {

   case 3: System.out.println("Three"); break;

   case 4: System.out.println("Four");

}

2(iv) Java Expression Writing
Write Java expression for:
p2+q2\sqrt{p^2 + q^2}

✅ Answer:

Math.sqrt((p * p) + (q * q));

2(v) Loop Execution & Output

int n = 5;

while(n < 8){

    System.out.println(n * n);

    n++;

}

✅ Answer:

  • Loop executes 3 times (n=5,6,7).
  • Output:

25

36

49

2(vi) String Methods

String s1 = "Hello", s2 = "HELLO";

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

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

✅ Answer:

false

true

2(vii) Character & ASCII Conversion

char c = 'd';

int val = (int)c + 5;

System.out.println((char)val + "\t" + c);

✅ Answer:

  • 'd' = ASCII 100
  • 100 + 5 = 105 → 'i'
  • Output:

i           d

2(viii) Error Type & Correction

String num = "100";

int x = Integer.parseInt(num);

double y = Math.sqrt(num);

System.out.println(y);

✅ Answer:

  • Error: Passing String directly in Math.sqrt() → compile-time error (syntax error).
  • Corrected Code:

String num = "100";

int x = Integer.parseInt(num);

double y = Math.sqrt(x);

System.out.println(y);

Output: 10.0

2(ix) Constructors

class Student {

   String name;

   int age;

   Student() {

      name = "Unknown";

      age = 0;

   }

   Student(String n, int a) {

      name = n;

      age = a;

   }

}

✅ Answer:

  • Default constructor → Student()
  • Parameterized constructor → Student(String n, int a)

2(x) 2D Array

int arr[][] = { {1,2,3}, {4,5,6}, {7,8,9} };

(a) Position of 8
(b) Value of arr[0][2] + arr[2][0]

✅ Answer:
(a) arr[2][1]
(b) 3 + 7 = 10

1. Armstrong Twins

👉 Definition: A number is Armstrong if sum of cubes of its digits = number itself.

Example:
153 → 13+53+33=1+125+27=1531^3 + 5^3 + 3^3 = 1 + 125 + 27 = 153 ✅
370 → 33+73+03=27+343+0=3703^3 + 7^3 + 0^3 = 27 + 343 + 0 = 370 ✅
📌 Hence, 153 and 370 are Armstrong Twins.

class ArmstrongTwins {

    public static void main(String args[]) {

        int a = 153, b = 370;

 

        int temp = a, sum = 0;

        while (temp > 0) {

            int d = temp % 10;

            sum += d * d * d;

            temp /= 10;

        }

        boolean first = (sum == a);

 

        temp = b; sum = 0;

        while (temp > 0) {

            int d = temp % 10;

            sum += d * d * d;

            temp /= 10;

        }

        boolean second = (sum == b);

 

        if (first && second)

            System.out.println(a + " and " + b + " are Armstrong Twins");

        else

            System.out.println("Not Armstrong Twins");

    }

}

2. Digit Rotation

👉 Rotate digits of a number left by one place.

Example:
Number = 12345
Step 1: Remove first digit → 2345
Step 2: Add removed digit at last → 23451
📌 Rotated result = 23451

class DigitRotation {

    public static void main(String args[]) {

        String num = "12345";

        String rotated = num.substring(1) + num.charAt(0);

        System.out.println("Rotated Number = " + rotated);

    }

}

3. Strong Number

👉 Sum of factorial of digits = number

Example:
145 → 1!+4!+5!1! + 4! + 5!
= 1+24+120=1451 + 24 + 120 = 145 ✅
📌 Hence, 145 is a Strong Number.

class StrongNumber {

    public static void main(String args[]) {

        int n = 145, temp = n, sum = 0;

 

        while (temp > 0) {

            int d = temp % 10;

            int f = 1;

            for (int i = 1; i <= d; i++) {

                f *= i;

            }

            sum += f;

            temp /= 10;

        }

 

        if (sum == n)

            System.out.println(n + " is Strong Number");

        else

            System.out.println(n + " is not Strong Number");

    }

}

4. Special Sum Number

👉 Sum of squares of digits + sum of digits = number

Example:
59 → Digits = 5, 9
Squares = 52+92=25+81=1065^2 + 9^2 = 25 + 81 = 106
Sum of digits = 5+9=145 + 9 = 14
Total = 106+14=120106 + 14 = 120
📌 So, 59 → 120 (Special Sum Result).

class SpecialSumNumber {

    public static void main(String args[]) {

        int n = 59, temp = n, sumSq = 0, sumD = 0;

 

        while (temp > 0) {

            int d = temp % 10;

            sumSq += d * d;

            sumD += d;

            temp /= 10;

        }

 

        int result = sumSq + sumD;

        System.out.println("Special Sum = " + result);

    }

}

5. Harshad–Palindrome

👉 Harshad = divisible by sum of digits; Palindrome = same backward.

Example:
171 → Digits = 1, 7, 1
Sum = 1+7+1=91 + 7 + 1 = 9
171÷9=19171 ÷ 9 = 19 ✅ Harshad
Also, Reverse of 171 = 171 ✅ Palindrome
📌 Hence, 171 is both Harshad & Palindrome.

class HarshadPalindrome {

    public static void main(String args[]) {

        int n = 171, temp = n, sum = 0;

 

        while (temp > 0) {

            sum += temp % 10;

            temp /= 10;

        }

        boolean harshad = (n % sum == 0);

 

        String s = Integer.toString(n);

        String rev = new StringBuilder(s).reverse().toString();

        boolean palindrome = s.equals(rev);

 

        if (harshad && palindrome)

            System.out.println(n + " is Harshad & Palindrome");

        else

            System.out.println(n + " is not Harshad & Palindrome");

    }

}

6. Digital Root

👉 Repeated sum of digits until single digit.

Example:
9875 → 9+8+7+5=299+8+7+5 = 29
29 → 2+9=112+9 = 11
11 → 1+1=21+1 = 2
📌 Digital root = 2

class DigitalRoot {

    public static void main(String args[]) {

        int n = 9875;

 

        while (n > 9) {

            int sum = 0;

            while (n > 0) {

                sum += n % 10;

                n /= 10;

            }

            n = sum;

        }

 

        System.out.println("Digital Root = " + n);

    }

}

7. Gapful Number

👉 At least 3 digits, divisible by first+last digit number.

Example:
192 → First digit = 1, Last digit = 2 → 12
Check divisibility: 192÷12=16192 ÷ 12 = 16 ✅
📌 Hence, 192 is Gapful.

class GapfulNumber {

    public static void main(String args[]) {

        String num = "192";

        int n = Integer.parseInt(num);

        int divisor = Integer.parseInt("" + num.charAt(0) + num.charAt(num.length() - 1));

 

        if (n % divisor == 0)

            System.out.println(n + " is Gapful Number");

        else

            System.out.println(n + " is not Gapful Number");

    }

}

8. Automorphic Number

👉 Square of number ends with the number itself.

Example:
76² = 5776 → ends with 76 ✅
📌 So, 76 is Automorphic.

class Automorphic {

    public static void main(String args[]) {

        int n = 76;

        long sq = (long) n * n;

 

        if (String.valueOf(sq).endsWith(String.valueOf(n)))

            System.out.println(n + " is Automorphic Number");

        else

            System.out.println(n + " is not Automorphic Number");

    }

}

 

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