🚨 Without DRY (Bad Practice – Code Duplication)
public class Calculator {
// Duplicated logic for addition
public int addIntegers(int a, int b) {
return a + b;
}
// Duplicated logic for doubles
public double addDoubles(double a, double b) {
return a + b;
}
public static void main(String[] args) {
Calculator calc = new Calculator();
System.out.println(calc.addIntegers(2, 3));
System.out.println(calc.addDoubles(2.5, 3.7));
}
}
🔴 Problem: The addition logic is duplicated for integers and doubles. If we want to extend to float, long, etc., duplication keeps increasing.
✅ With DRY (Good Practice – Reusable Code)
Example 1: Using Generics
public class Calculator {
// DRY: Generic method for addition
public <T extends Number> double add(T a, T b) {
return a.doubleValue() + b.doubleValue();
}
public static void main(String[] args) {
Calculator calc = new Calculator();
System.out.println(calc.add(2, 3)); // int
System.out.println(calc.add(2.5, 3.7)); // double
System.out.println(calc.add(5L, 10L)); // long
}
}
✅ One method works for all number types → no duplication.
Example 2: Extracting Reusable Logic
public class AreaCalculator {
// DRY: Common reusable method
public double calculateArea(double length, double width) {
return length * width;
}
public static void main(String[] args) {
AreaCalculator calc = new AreaCalculator();
// Rectangle
System.out.println("Rectangle Area: " + calc.calculateArea(5, 10));
// Square (uses same method)
System.out.println("Square Area: " + calc.calculateArea(6, 6));
}
}
✅ Instead of writing separate methods for rectangle and square, we reuse one method.
👉 Summary:
- DRY in Java means removing duplicate logic by using methods, classes, generics, inheritance, or interfaces.
- This makes the code shorter, easier to maintain, and less error-prone.