Operator precedence in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to correctly calculate the result using operator precedence.

Java

int result = 5 + 3 [1] 2;

Drag options to blanks, or click blank then click option'

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using + instead of * causes the addition to happen first, changing the result.

The multiplication operator (*) has higher precedence than addition, so 3 * 2 is calculated first, then added to 5.

2fill in blank

medium

Complete the code to correctly evaluate the expression considering operator precedence.

Java

int value = 10 - 4 [1] 2;

Drag options to blanks, or click blank then click option'

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using + instead of * changes the operation order and result.

The multiplication operator (*) has higher precedence than subtraction, so 4 * 2 is calculated first, then subtracted from 10.

3fill in blank

hard

Fix the error in the expression to respect operator precedence and get the correct result.

Java

int output = 20 / 4 [1] 2;

Drag options to blanks, or click blank then click option'

A/

B*

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using * or / again changes the order and result unexpectedly.

Division and multiplication have the same precedence and are evaluated left to right. Using subtraction (-) after division changes the result correctly.

4fill in blank

hard

Fill both blanks to create a map of numbers to their doubled values only if the number is greater than 3.

Java

Map<Integer, Integer> squares = IntStream.range(1, 6)
    .filter(n -> n [1] 3)
    .boxed()
    .collect(Collectors.toMap(n -> n, n -> n [2] 2));

Drag options to blanks, or click blank then click option'

A>

B*

C<

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of > in filter selects wrong numbers.

Using + instead of * does addition, not doubling.

The filter uses > to select numbers greater than 3. The map doubles each number using the * operator.

5fill in blank

hard

Fill all three blanks to create a map of uppercase strings to their lengths only if the length is greater than 4.

Java

Map<String, Integer> result = words.stream()
    .filter(word -> word.length() [1] 4)
    .collect(Collectors.toMap(word -> word.[2](), word -> word.[3]()));

Drag options to blanks, or click blank then click option'

A<

Blength

C>

DtoUpperCase

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of > in filter.

Using length instead of toUpperCase for keys.

Using toUpperCase instead of length for values.

The filter uses > to select words longer than 4 characters. The map uses toUpperCase() for keys and length() for values.

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