Calculate Area of Rectangle in Java
beginner· Basics & I/O · Geometry
Problem
A rectangle's area is simply its length multiplied by its width — no special constants or functions needed.
Given the length and width of a rectangle, calculate its area.
Input
length = 10.0, width = 5.0
Output
Area: 50.0
Java Program
Java
public class CalculateAreaOfRectangle {
public static void main(String[] args) {
double length = 10.0;
double width = 5.0;
double area = length * width; // length times width
System.out.println("Area: " + area);
}
}Output
Area: 50.0
Core Logic
Multiplying length by width gives the area directly, in a single expression.
How It Works
- 1
lengthholds10.0andwidthholds5.0. - 2
length * widthevaluates to50.0. - 3The result is stored in
areaand printed with a label.
For
length = 10.0 and width = 5.0, 10.0 * 5.0 gives 50.0.💡
Key Point: A rectangle where length equals width is a square — the same formula works either way, since a square is just a special case of a rectangle.
Key Concepts
doublemultiplication
Approach 2: Java 8
Java
import java.util.function.DoubleBinaryOperator;
public class CalculateAreaOfRectangleLambda {
public static void main(String[] args) {
double length = 10.0;
double width = 5.0;
// The multiplication logic is stored as a lambda, named for what it computes
DoubleBinaryOperator areaOf = (l, w) -> l * w;
double area = areaOf.applyAsDouble(length, width);
System.out.println("Area: " + area);
}
}
Output
Area: 50.0
Core Logic
The multiplication can be wrapped in a named lambda, turning 'compute an area' into a small reusable function.
How It Works
- 1
DoubleBinaryOperator areaOf = (l, w) -> l * w;stores the multiplication logic as a lambda. - 2
areaOf.applyAsDouble(length, width)calls it, returning the same result the inline multiplication would. - 3The result is printed exactly as before.
With
length = 10.0 and width = 5.0, areaOf.applyAsDouble(10.0, 5.0) returns 50.0.💡
Key Point: Naming the lambda areaOf instead of a generic multiply makes the intent clear at the call site, even though the underlying operation is just multiplication.
Key Concepts
DoubleBinaryOperatorfunctional interfacelambda expression