Assignment operators in Java

Introduction

Assignment operators help you store values in variables easily. They let you update variables quickly without writing long code.

When you want to save a value into a variable.

When you want to add or subtract a number from a variable's current value.

When you want to multiply or divide a variable by a number and save the result.

When you want to combine assignment with a math operation in one step.

When you want to update a variable based on its current value.

Syntax

Java

variable = value;
variable += value;
variable -= value;
variable *= value;
variable /= value;
variable %= value;

The = operator assigns a value to a variable.

Operators like += combine math and assignment in one step.

Examples

Assign 5 to variable x.

Java

int x = 5;

Add 3 to x and save the result back to x.

Java

x += 3;  // same as x = x + 3;

Multiply x by 2 and save the result back to x.

Java

x *= 2;  // same as x = x * 2;

Set x to the remainder when x is divided by 4.

Java

x %= 4;  // same as x = x % 4;

Sample Program

This program shows how to use different assignment operators to change the value of score. It prints the value after each change.

Java

public class Main {
    public static void main(String[] args) {
        int score = 10;
        System.out.println("Initial score: " + score);
        score += 5;
        System.out.println("After adding 5: " + score);
        score -= 3;
        System.out.println("After subtracting 3: " + score);
        score *= 2;
        System.out.println("After multiplying by 2: " + score);
        score /= 4;
        System.out.println("After dividing by 4: " + score);
        score %= 3;
        System.out.println("After modulo 3: " + score);
    }
}

Important Notes

Assignment operators make code shorter and easier to read.

Be careful with division and modulo to avoid dividing by zero.

Summary

Assignment operators store or update values in variables.

Operators like +=, -=, *= combine math and assignment.

They help write cleaner and shorter code.

Practice

1. What does the assignment operator += do in Java?

easy

A. Divides the left variable by the right value

B. Subtracts the right value from the left variable

C. Multiplies the left variable by the right value

D. Adds the right value to the left variable and stores the result in the left variable

Solution

1. Step 1: Understand the += operator

   The += operator adds the right-hand side value to the left-hand side variable.

2. Step 2: Store the result back in the left variable

   The sum replaces the original value in the left variable.

3. Final Answer:

   Adds the right value to the left variable and stores the result in the left variable -> Option D

4. Quick Check:

   x += y means x = x + y [OK]

Hint: Think: add then assign back to the same variable [OK]

Common Mistakes:

• Confusing += with subtraction or multiplication
• Thinking it only adds without assignment
• Mixing up the order of operands

2. Which of the following is the correct syntax to multiply a variable num by 5 and assign the result back to num?

easy

A. num = * 5;

B. num *= 5;

C. num = num *;

D. num = 5 *;

Solution

1. Step 1: Identify the correct compound assignment syntax

   The operator *= multiplies and assigns in one step.

2. Step 2: Check the variable and value placement

   The correct form is num *= 5; which means num = num * 5;.

3. Final Answer:

   num *= 5; -> Option B

4. Quick Check:

   Use *= for multiply and assign [OK]

Hint: Look for operator before equals for combined action [OK]

Common Mistakes:

• Placing * after = without variable
• Leaving out the variable on right side
• Using invalid syntax like num = * 5

3. What is the output of this Java code?

int a = 10;
a -= 3;
a += 2;
System.out.println(a);

medium

A. 9

B. 11

C. 5

D. 15

Solution

1. Step 1: Calculate a -= 3;

   Subtract 3 from 10: 10 - 3 = 7, so a becomes 7.

2. Step 2: Calculate a += 2;

   Add 2 to 7: 7 + 2 = 9, so a becomes 9.

3. Step 3: Check the printed value

   The code prints the current value of a, which is 9.

4. Final Answer:

   9 -> Option A

5. Quick Check:

   10 - 3 + 2 = 9 [OK]

Hint: Perform each assignment step in order carefully [OK]

Common Mistakes:

• Adding before subtracting
• Mixing up += and -= effects
• Printing before assignment changes

4. Find the error in this code snippet:

int x = 5;
x + = 3;
System.out.println(x);

medium

A. Variable x is not initialized

B. Missing semicolon after System.out.println(x)

C. The operator + = has a space and is invalid

D. The code will print 8 without errors

Solution

1. Step 1: Check the operator syntax

   The operator += must not have spaces; + = is invalid.

2. Step 2: Confirm other syntax elements

   Variable x is initialized and semicolons are correct.

3. Final Answer:

   The operator + = has a space and is invalid -> Option C

4. Quick Check:

   No spaces allowed in compound assignment operators [OK]

Hint: Compound operators have no spaces, write as one token [OK]

Common Mistakes:

• Adding spaces inside operators
• Assuming code runs despite syntax errors
• Confusing initialization errors with operator errors

5. Given the code below, what is the final value of total?

int total = 20;
int discount = 5;
total -= discount *= 2;
System.out.println(total);

hard

A. 10

B. 30

C. 15

D. 5

Solution

1. Step 1: Evaluate discount *= 2;

   This multiplies discount by 2: 5 * 2 = 10, so discount becomes 10.

2. Step 2: Calculate total -= discount;

   Subtract discount (now 10) from total (20): 20 - 10 = 10.

3. Step 3: Confirm final value

   The final value of total is 10, which is printed.

4. Final Answer:

   10 -> Option A

5. Quick Check:

   discount = 5*2=10; total = 20-10=10 [OK]

Hint: Evaluate right side first in compound assignments [OK]

Common Mistakes:

• Ignoring that discount changes before subtraction
• Subtracting original discount value (5) instead of updated (10)
• Confusing order of operations in assignment