Operator precedence in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Java code involving mixed operators?

Consider the following Java code snippet:

int result = 3 + 4 * 2 / (1 - 5) % 2;

What is the value of result after this code runs?

Java

int result = 3 + 4 * 2 / (1 - 5) % 2;
System.out.println(result);

A 1

B 3

C 0

D -1

💡 Hint

Remember the order: parentheses, multiplication/division/modulus, then addition/subtraction.

Step by step:
Parentheses: (1 - 5) = -4
4 * 2 = 8
8 / -4 = -2 (integer division)
-2 % 2 = 0
3 + 0 = 3

❓ Predict Output

intermediate

What is the output of this Java expression with logical and bitwise operators?

Given the code:

int a = 5; // binary 0101
int b = 3; // binary 0011
boolean result = a > 2 && b < 5 | a == 5;

What is the value of result?

Java

int a = 5;
int b = 3;
boolean result = a > 2 && b < 5 | a == 5;
System.out.println(result);

A true

B false

C Compilation error

D Runtime exception

💡 Hint

Check operator precedence between && and | in Java.

Operator precedence: && has higher precedence than | (bitwise OR).
So expression is evaluated as: (a > 2 && b < 5) | a == 5
a > 2: true (5>2)
b < 5: true (3<5)
a == 5: true
true && true = true
true | true = true

🔧 Debug

advanced

What error does this Java code produce due to operator precedence?

Examine this code snippet:

int x = 10;
int y = 20;
boolean check = x < y && x++ > 5 || y-- < 15;

What error or output does this code produce?

Java

int x = 10;
int y = 20;
boolean check = x < y && x++ > 5 || y-- < 15;
System.out.println(check);
System.out.println(x);
System.out.println(y);

A true, x=11, y=20

B true, x=11, y=19

C false, x=10, y=19

D Compilation error

💡 Hint

Remember the order of evaluation and side effects of post-increment and post-decrement.

Operator precedence: && higher than ||.
Expression: (x < y && x++ > 5) || (y-- < 15)
x=10, y=20
x < y: true
x++ > 5: post-increment uses 10 > 5 (true), then x=11
true && true = true
|| short-circuits (left true), so y-- not evaluated, y=20
Output: true, 11, 20

📝 Syntax

advanced

Which option causes a syntax error due to operator misuse in Java?

Which of the following Java code snippets will cause a syntax error?

A int d = 7 % 3 + 1;

B int b = (4 + 5) * 2;

C int c = 10 / 2 - 3;

D int a = 5 + * 3;

💡 Hint

Look for invalid operator combinations.

Option D has 5 + * 3 which is invalid syntax.
Options A, B, and C are valid arithmetic expressions.

🚀 Application

expert

How many items are in the resulting array after this Java expression?

Consider this Java code:

int[] arr = {1, 2, 3, 4, 5};
int[] result = new int[arr.length];
for (int i = 0; i < arr.length; i++) {
    result[i] = arr[i]++ * --arr[i];
}

How many elements in result are greater than 0 after this loop?

Java

int[] arr = {1, 2, 3, 4, 5};
int[] result = new int[arr.length];
for (int i = 0; i < arr.length; i++) {
    result[i] = arr[i]++ * --arr[i];
}
int count = 0;
for (int val : result) {
    if (val > 0) count++;
}
System.out.println(count);

A 4

B 2

C 5

D 3

💡 Hint

Understand how post-increment and pre-decrement affect the value used in multiplication.

For each i, arr[i]++ * --arr[i]:
- arr[i]++: uses original n, then arr[i] = n+1
- --arr[i]: arr[i] = n, uses n
- n * n = n² > 0 for all original values 1-5
Operations cancel out per element, result = [1,4,9,16,25], all >0, count=5

Practice

1. Which operator has the highest precedence in the expression 3 + 4 * 5?

easy

A. Subtraction (-)

B. Addition (+)

C. Division (/)

D. Multiplication (*)

Solution

1. Step 1: Identify operators in the expression

   The expression has addition (+) and multiplication (*).

2. Step 2: Recall operator precedence rules

   Multiplication (*) has higher precedence than addition (+), so it runs first.

3. Final Answer:

   Multiplication (*) -> Option D

4. Quick Check:

   Multiplication > Addition [OK]

Hint: Multiplication and division run before addition and subtraction [OK]

Common Mistakes:

• Thinking addition runs before multiplication
• Ignoring operator precedence
• Assuming left to right always applies

2. Which of the following expressions is syntactically correct in Java?

easy

A. int result = 5 + (3 * 2);

B. int result = 5 + * 3;

C. int result = 5 + 3 *;

D. int result = 5 + 3 * 2))

Solution

1. Step 1: Check each expression for syntax errors

   int result = 5 + * 3; has an invalid operator sequence '+ *'. int result = 5 + 3 *; ends with '*;' which is incomplete. int result = 5 + 3 * 2)) has unmatched parentheses.

2. Step 2: Validate correct syntax

   int result = 5 + (3 * 2); uses parentheses properly and valid operators, so it is correct.

3. Final Answer:

   int result = 5 + (3 * 2); -> Option A

4. Quick Check:

   Valid syntax uses proper operators and balanced parentheses [OK]

Hint: Check for balanced parentheses and valid operator placement [OK]

Common Mistakes:

• Leaving operators without operands
• Unbalanced parentheses
• Using invalid operator sequences

3. What is the output of the following Java code?

int x = 2 + 3 * 4 - 6 / 2;
System.out.println(x);

medium

A. 12

B. 10

C. 11

D. 14

Solution

1. Step 1: Apply operator precedence to the expression

   Multiplication and division run before addition and subtraction:
   3 * 4 = 12
   6 / 2 = 3

2. Step 2: Calculate the expression left to right

   Expression becomes: 2 + 12 - 3
   2 + 12 = 14
   14 - 3 = 11

3. Final Answer:

   11 -> Option C

4. Quick Check:

   2 + (3*4) - (6/2) = 11 [OK]

Hint: Do multiplication/division first, then addition/subtraction [OK]

Common Mistakes:

• Adding before multiplying
• Ignoring division precedence
• Calculating left to right without precedence

4. The following code throws a compilation error. What is the cause?

int a = 5;
int b = 10;
int c = a + * b;

medium

A. Incorrect variable declaration

B. Missing operand between + and * operators

C. Missing semicolon at the end

D. Using undeclared variable

Solution

1. Step 1: Analyze the expression syntax

   The expression 'a + * b' has two operators '+' and '*' without a number or variable between them, which is invalid.

2. Step 2: Identify the compilation error cause

   Java expects an operand between operators. The missing operand causes a syntax error.

3. Final Answer:

   Missing operand between + and * operators -> Option B

4. Quick Check:

   Operators must have operands between them [OK]

Hint: Check for missing operands between operators [OK]

Common Mistakes:

• Assuming multiple operators can be together
• Ignoring syntax errors
• Confusing variable declaration with expression errors

5. Consider the expression:

int result = 10 - 2 * 3 + 4 / 2;

How can you change the expression using parentheses to make addition happen before multiplication and subtraction?

hard

A. int result = 10 - (2 * (3 + 4 / 2));

B. int result = (10 - 2) * (3 + 4) / 2;

C. int result = 10 - ((2 * 3) + (4 / 2));

D. int result = 10 - (2 * 3 + 4) / 2;

Solution

1. Step 1: Understand original precedence

   Original expression evaluates multiplication and division first:
   2 * 3 = 6
   4 / 2 = 2
   Then subtraction and addition left to right:
   10 - 6 + 2 = 6

2. Step 2: Use parentheses to make addition happen before multiplication and subtraction

   To add before multiplication, group inside parentheses:
   3 + 4 / 2
   Since division has higher precedence, 4 / 2 = 2, so 3 + 2 = 5
   Expression becomes:
   10 - (2 * 5) = 10 - 10 = 0

3. Final Answer:

   int result = 10 - (2 * (3 + 4 / 2)); -> Option A

4. Quick Check:

   Parentheses change order to add before multiply [OK]

Hint: Use parentheses to group operations you want first [OK]

Common Mistakes:

• Misplacing parentheses changing meaning
• Ignoring division precedence inside parentheses
• Assuming parentheses don't affect order