Java Reference
In-Depth Information
Self-review exercises
SR1 . The range in the schema in Fig. 7.2 can be generalized. Rewrite it so that
it processes the natural numbers in the range i..j-1 rather than 0..n-1 .
SR2 . Use the schema in Fig. 7.2 to write a loop to find the number of vowels in
a String s . Hint: declare a new String that contains the five vowels, and use
the fact that String method indexOf returns -1 if the char argument is not in
the String of vowels.
SR3 . How many numbers are there in the range i..j-1 ?
Answers to self review exercises
SR1. // Process the natural numbers i..j-1 (for j≥i)
int k= i;
// { invariant: i..k-1 have been processed }
while (k != j) {
Process k;
k= k + 1;
// {i..j-1 have been processed }
SR2. // Set x to the number of vowels in s[0..s.length()-1]
int k= 0; x= 0;
String vowels = "aeiou";
// { invariant: x = number of vowels in s[0..k-1] }
while (k != s.length()) {
if (vowels.indexOf(s.charAt(k)) != -1) {
x= x + 1;
k= k + 1;
// { x = number of vowels in s[0..s.length()-1] }
SR3. j-i+1
The for-loop
The for-loop as an abbreviation
Besides the while-loop, Java has an iterative statement called the for-loop . The
for-loop can be viewed as an abbreviation of a certain kind of while-loop. Here
is an example. The following loop draws n concentric circles:
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