🔢 Purpose of the Program

This program prints Fibonacci numbers that are less than 89.

🧠 Understanding the Code 

public class Fibonacci {

This defines a public class named Fibonacci.

public static void main(String[] args) {

This is the main method—where the program starts execution.

int f = -1;
int s = 1;
int t = 0;

These are integer variables:

  • f is initialized to -1
  • s is initialized to 1
  • t is initialized to 0

These will be used to calculate Fibonacci numbers.

Note: Fibonacci starts with 0, 1, 1, 2, 3, 5...

Using f = -1 and s = 1 makes the first sum 0 (-1 + 1).

while(t < 89){

Loop continues as long as the current number (t) is less than 89.

t = f + s;

Calculate the next number in the Fibonacci sequence.

System.out.println(t);

Print the current Fibonacci number.

f = s;
s = t;

Update variables to prepare for the next Fibonacci number:

  • f becomes the old s
  • s becomes the new t

📌 Sample Output

This prints:

0
1
2
3
5
8
13
21
34
55
89

Even though the condition is t < 89, it still prints 89, because the condition is checked after t is calculated and printed.

✅ Summary

This is a simple and clever way to generate Fibonacci numbers using just a while loop and 3 variables. It avoids arrays or recursion.

Would you like the same program using recursion or with user input for the limit?