Operator precedence in Java - Step-by-Step Execution

Concept Flow - Operator precedence

Start Expression

↓

Identify Operators

↓

Check Precedence Levels

↓

Evaluate Highest Precedence Operator

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Replace with Result

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Repeat Until Expression Fully Evaluated

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Final Result

The expression is evaluated by first identifying operators, then applying them in order of their precedence from highest to lowest until the entire expression is evaluated.

Execution Sample

Java

int result = 3 + 4 * 2;
System.out.println(result);

Calculates 3 plus 4 times 2, showing how multiplication happens before addition.

Execution Table

Step	Expression	Operator Evaluated	Operation	Resulting Expression
1	3 + 4 * 2	*	4 * 2 = 8	3 + 8
2	3 + 8	+	3 + 8 = 11	11
3	11	None	Expression fully evaluated	11

💡 No more operators left, final result is 11

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
result	undefined	undefined	undefined	11

Key Moments - 2 Insights

Why does multiplication happen before addition in the expression?

Because multiplication has higher precedence than addition, as shown in step 1 of the execution_table where 4 * 2 is evaluated before adding 3.

What if we want addition to happen first?

We can use parentheses to change precedence, for example (3 + 4) * 2, which would evaluate addition first.

Visual Quiz - 3 Questions

Look at the execution_table, what is the expression after step 1?

A 3 + 8

B 7 * 2

C 3 + 4

D 11

💡 Hint

Check the 'Resulting Expression' column in row for step 1.

At which step is the addition operator evaluated?

A Step 1

B Step 2

C Step 3

D Never

💡 Hint

Look at the 'Operator Evaluated' column to find when '+' is processed.

If the expression was (3 + 4) * 2, what would be the first operation evaluated?

A 3 * 2

B 4 * 2

C 3 + 4

D Addition and multiplication at the same time

💡 Hint

Parentheses change precedence, so check what is inside them first.

Concept Snapshot

Operator precedence determines the order in which parts of an expression are calculated.
Higher precedence operators (like *) are evaluated before lower ones (like +).
Use parentheses () to change the order explicitly.
Example: 3 + 4 * 2 equals 3 + (4 * 2) = 11.
Without parentheses, multiplication and division happen before addition and subtraction.

Full Transcript

Operator precedence in Java means some operations happen before others in an expression. For example, multiplication (*) has higher precedence than addition (+). In the code 'int result = 3 + 4 * 2;', the multiplication 4 * 2 is done first, resulting in 8, then 3 + 8 equals 11. This is shown step-by-step in the execution table. If you want addition first, use parentheses like (3 + 4) * 2. This changes the order and the result. Understanding operator precedence helps avoid mistakes and write correct expressions.

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