Loops - Learning Java Through Games - page 51

23 for ( int line = 0; line < s i z e / 2 ; l i n e ++) {

24 for ( int i=0;i < numSpaces ; i++) {

25 System . out . p r i n t ( "" );

26 }

27 for ( int i=0;i < numStars ; i++) {

28 System . out . p r i n t ( "* " );

29 }

30 System . out . p r i n t l n ( ) ;

31 numSpaces += 2;

32 numStars − =2;

33 }

}

34

}

35

Lines 8-20 print the top part of the diamond, while Lines 21-33 print the bottom half.
Note that the variable i is used as a counter. Traditionally, the counter is referred to as
an iterator by programmers and, as a consequence, i is a common name for the counter
variable. The first part of the code tells the computer to print siz 2 + 1 lines. The variable
line is used as the counter variable. When printing a line, we print numSpaces spaces and
numStars stars. Next, we update the value of the variables. Note that Line 17 prints a new
line. The println method does not require a parameter. If it is called without a parameter,
then just a new line is printed.
An experienced programmer probably will not introduce the variable line . The reason is
that either the variable numSpaces or the variable numStars can be used to decide when to
stop the for loop. We will keep executing the first for loop while the numSpaces is greater
or equal to 0. We will keep executing the second for loop while the numStars is greater or
equal to 0. Note that the condition inside the for statement is exactly the opposite (or the
negation) of the loop terminating condition.

import java . util . ∗ ;

public class Diamond {
public static void main(String [] args) {
Scanner keyboard = new Scanner(System. in) ;
System. out . print ( "Enter size of diamond: " );
int size = keyboard.nextInt() ;
for ( int numStars =1, numSpaces = size

− >

1; numSpaces =0; numSpaces

− =2, numStars+=2) {

for ( int i=0;i < numSpaces ; i++) {

System. out . print ( "" );
for ( int i=0;i < numStars ;

i++) {

System. out . print ( "* " );
System. out . println () ;
for ( int numStars=size − 2, numSpaces = 2; numStars > 0; numSpaces+=2,
numStars − =2 ) {
for ( int i=0;i < numSpaces ;

i++) {

System. out . print ( "" );
for ( int i=0;i < numStars ;

i++) {

System. out . print ( "* " );
System. out . println () ;