Loops (For...next)
Most applications require the
computer to perform repetitive tasks.
Java allows the use of For ...next , While and Do While loops.
The syntax of the For...next loop in Java is very similar to C++
for ( n = 1; n < 100; n++) will loop through any following block of code 100 times.
The loop starts out by initializing the integer variable n to equal 1.
It then executes the block of code once and returns to the loop statement.
The n++ arithmetic operator is then executed which increments n.
If n is less than 100 it will again execute the block of code.
This process repeats until the condition n < 100 is false.
Copy the following code into a
text editor and
save it as forloop.java.
| class forloop { public static void main (String args[]){ int x; for (x=0 ; x<20 ; x++) System.out.println("x = " + x + " x squared = " + 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. It starts at x = 0 Line 5 sends the values for Notice how the string is concatenated |
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 x < 20 could be changed to x <= 20 if we wanted the loop to continue to that point.