Lesson 8: Arithmetic & Assignment Operators in Java

What is an Arithmetic Operator?

Imagine you’re calculating your monthly expenses or figuring out how long it will take to get to your destination. Arithmetic operators are like the buttons on a calculator that perform the math for you.

Example:

int a = 5;
int b = 2;
int result = a + b; // The "+" operator adds the numbers
System.out.println(result); // Output: 7

Basic Arithmetic Operators

Java provides several basic arithmetic operators to perform fundamental mathematical operations:

Division: Integers and Decimals

When you divide integers in Java, the fractional part of the result is simply removed. This process is called truncation, and it always rounds down to the nearest whole number, regardless of whether the number is positive or negative. It is important to note that truncation is different from rounding, where numbers are adjusted up or down based on their value.

Example:

int a = 5;
int b = 2;
System.out.println(a / b); // Result: 2

In this example, the mathematical result of 5 / 2 would be 2.5, but Java only keeps the integer part, discarding the fractional part entirely. The result is 2.

To get the exact value (e.g., 2.5), you need to use floating-point numbers (double):

Example:

double x = 5.0;
double y = 2.0;
System.out.println(x / y); // Result: 2.5

Remainder (%)

The % operator calculates the remainder of a division. It answers the question, “What is left after dividing one number by another?”

Example:

int a = 5;
int b = 2;
System.out.println(a % b); // Result: 1

Explanation:
When dividing 5 by 2, the largest number divisible by 2 is 4 (4 / 2 = 2). Subtracting 4 from 5 leaves a remainder of 1. That’s the result of 5 % 2.

The % operator is particularly useful for checking if a number is even or odd:

Example:

int number = 10;
if (number % 2 == 0) {
    System.out.println("Even"); // This code runs if the condition is true
} else {
    System.out.println("Odd"); // This code runs if the condition is false
}

Using Conditional Statements (if-else)

The if-else statement allows your program to decide between two actions: one action is executed if the condition is true, and another action is executed if the condition is false.

Example:

int number = 15;
if (number % 2 == 0) {
    System.out.println("Even"); // This code runs if the condition is true
} else {
    System.out.println("Odd"); // This code runs if the condition is false
}

Operator Precedence in Java

Just like in mathematics, Java follows rules for the order of operations, known as operator precedence. Multiplication and division are performed before addition and subtraction.

Example:

int result = 5 + 2 * 3; // Multiplication first, then addition
System.out.println(result); // Result: 11

If you want to change the order of operations, use parentheses to specify the priority:

Example:

int result = (5 + 2) * 3; // Parentheses first
System.out.println(result); // Result: 21

Parentheses make the code clearer and ensure operations are executed in the desired order.

Wrap-Up

Arithmetic operators are essential for performing calculations in Java. Understanding their behavior, especially integer division, the remainder operator, and operator precedence, is critical for writing accurate and efficient code.

When dividing integers, remember that Java truncates results instead of rounding. Use floating-point numbers for more precise calculations. Finally, always use parentheses to clarify and control the order of operations in complex expressions.

What Are Assignment Operators?

When we write programs, we need to store and work with data. For example, you might want to save a number, a name, or something else. To do this, we use variables. To place a value into a variable, we use an assignment operator.

An assignment operator is simply the = symbol. It tells the program:
“Take this value and put it into this variable.”

Example:

int age = 30;

Here’s what happens:

1. int — We declare a variable of type integer (a whole number).
2. age — The name of the variable.
3. = — The assignment operator.
4. 30 — The value we assign to the variable age.

Now, the variable age holds the value 30. If we write:

System.out.println(age);

The program will output:

30

Changing Values in a Variable

You can change the value stored in a variable using the assignment operator =.

Example:

age = 35;
System.out.println(age);

Now, the variable age holds the value 35. When a new value is assigned, the old value is overwritten.

Shortened Assignment Operators

Java allows you to combine assignment with arithmetic operations like addition, subtraction, multiplication, etc. These are called shortened assignment operators.

Examples of Shortened Assignment Operators:

1. Addition: +=

int x = 10;
x += 5; // Same as x = x + 5;
System.out.println(x); // Output: 15

2. Subtraction: -=

int y = 20;
y -= 8; // Same as y = y - 8;
System.out.println(y); // Output: 12

3. Multiplication: *=

int z = 7;
z *= 3; // Same as z = z * 3;
System.out.println(z); // Output: 21

4. Division: /=

int a = 40;
a /= 4; // Same as a = a / 4;
System.out.println(a); // Output: 10

5. Remainder (modulus): %=

int b = 17;
b %= 3; // Same as b = b % 3;
System.out.println(b); // Output: 2 (the remainder when 17 is divided by 3)

Real-Life Example: A Piggy Bank

Imagine you have a piggy bank to store your money:

1. When you put 50 dollars in it, you use the = operator:

int piggyBank = 50;

2. If you add another 30 dollars, you use the += operator:

piggyBank += 30; // Now the piggy bank contains 80 dollars

3. If you spend 20 dollars, you use the -= operator:

piggyBank -= 20; // Now the piggy bank contains 60 dollars

Important Note: Assignment Is Not Math Equality

The assignment operator = does not mean equality in the mathematical sense.

For example:

x = x + 1;

In math, this would seem impossible. But in programming, it means:
“Take the current value of x, add 1 to it, and store the result back into x.”

Key Points to Remember:

1. The assignment operator = places a value into a variable.
2. Variables can be updated with new values, replacing the old ones.
3. Shortened assignment operators like +=, -= simplify combining arithmetic and assignment.
4. In programming, = does not mean equality — it means assignment.

With assignment operators, you can store and update values in your variables as your program runs. This is an essential tool for creating dynamic, flexible programs!