Operator precedence in Java - Mini Project: Build & Apply

Operator precedence

📖 Scenario: You are creating a simple calculator program that evaluates an expression using different operators. Understanding the order in which Java applies these operators is important to get the correct result.

🎯 Goal: Build a Java program that calculates the value of an expression using operator precedence rules and prints the correct result.

📋 What You'll Learn

Create variables with given values

Use a configuration variable for a multiplier

Calculate an expression using operator precedence

Print the final result

💡 Why This Matters

🌍 Real World

Understanding operator precedence helps you write correct calculations in programs like calculators, financial software, or games.

💼 Career

Many programming jobs require you to write expressions that combine multiple operations correctly, so knowing operator precedence is essential.

1

Create initial variables

Create three integer variables called a, b, and c with values 5, 10, and 2 respectively.

Java

// Your code here

Hint

Use the syntax int variableName = value; to create each variable.

2

Add a multiplier variable

Create an integer variable called multiplier and set it to 3.

Java

int a = 5;
int b = 10;
int c = 2;
// Your code here

Hint

Remember to end the line with a semicolon.

3

Calculate expression with operator precedence

Create an integer variable called result and assign it the value of the expression a + b * c * multiplier. Use the exact variable names and operators as shown.

Java

int a = 5;
int b = 10;
int c = 2;
int multiplier = 3;
// Your code here

Hint

Remember that multiplication happens before addition in operator precedence.

4

Print the result

Write a line to print the value of result using System.out.println.

Java

int a = 5;
int b = 10;
int c = 2;
int multiplier = 3;
int result = a + b * c * multiplier;
// Your code here

Hint

Use System.out.println(result); to display the value.

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