Loops (While Loops)
The while loop is used to repeat a block of code as long as a particular condition is true.
The syntax of the while loop in Java is
While (condition) {
block of code
}
The following application will result in the same printout as the For - Next program we looked at in the last section.
Copy the following code into a
text editor and
save it as whileloop.java.
class whileloop {
public static void main (String args[]){
int x = 0; while (x<20) {
System.out.println("x = " + x + " x squared = " + x*x);
x++; }
}
}
|
Line 1 Designates that we are defining a new class called forloop. Line 3 declares x as an integer variable Line 4 sets up the loop conditions. Line 5 sends the values for Line 6 increments x |
After compiling and running this program the output should be
x = 0 x squared = 0 x = 1 x squared = 1 x = 2 x squared = 4 x = 3 x squared = 9 x = 4 x squared = 16 x = 5 x squared = 25 x = 6 x squared = 36 x = 7 x squared = 49 x = 8 x squared = 64 x = 9 x squared = 81 x = 10 x squared = 100 x = 11 x squared = 121 x = 12 x squared = 144 x = 13 x squared = 169 x = 14 x squared = 196 x = 15 x squared = 225 x = 16 x squared = 256 x = 17 x squared = 289 x = 18 x squared = 324 x = 19 x squared = 361
Notice that x = 20 is not printed. The value of x actually does get to 20 but the loop exits at that point therefore it is never printed. The controlling decision While (x < 20) could be changed to x <= 20 if we wanted the loop to continue to that point.
The Do While loop is very similar except that it executes a given statement until the condition is false.
A loop can be used to accept all command line arguments as you can see in this example.
Go to the next topic: Arrays