final parameters
- Java course
- Beginner
- Lesson 81/116
- 4 min
Learn immutability with final parameters.
final parameters
If you mark a parameter as final, it cannot be reassigned inside the method. This prevents accidental changes to the parameter and clearly shows the intent of the code.
static int doubleOf(final int x) {
// x = 10; // compile error
return x * 2;
}Here, reassigning x is a compile error. final parameters become especially important in lambdas and inner classes; there, outer variables must be effectively final.
Practical use of final
final parameters are not always necessary; but they make intent clear. Especially when the method body is long, guaranteeing that the parameter does not change is valuable.
static void printArea(final int width, final int height) {
int area = width * height;
System.out.println("Area: " + area);
}Here width and height are constant throughout the method. This gives confidence to whoever reads the code. On the call side, final has no effect.
Practice Compute area (with final)
Define a static void method called printArea; parameters final int width, final int height. The body should compute the area and print it as Area: <area>. Call printArea(5, 3) from main.
Starter code
public class Main {
public static void main(String[] args) {
// Call the method with 5 and 3
}
// Define the printArea method here
}Sample solution
static void printArea(final int width, final int height) {
System.out.println("Area: " + (width * height));
}
// inside main:
printArea(5, 3);Expected output
Area: 15
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which is a compile error in a method with a final int x parameter?
- int y = x + 1;
- x = 10; Correct answer
- return x * 2;
- System.out.println(x);
Explanation: A final parameter cannot be reassigned.
2 Fill in the blank: final parameter
static int doubleOf(____ int x) {
return x * 2;
}static int doubleOf(final int x) {
return x * 2;
}Explanation: With final int x, the parameter cannot be changed.
3 Match keyword to role
| Term | Meaning |
|---|---|
static |
Defines at class level |
final |
Prevents reassignment |
void |
Returns no value |
return |
Hands a value out |