Can anyone help me understand "Continue Statements"?

Question

Hi,
I was wondering if anyone could help me understand continue statements. I've been studying the java tutorials this weekend but can not get my head around the following explanation: (My thoughts are at the end of this message and it might be easiest to read them first!)
"The continue statement skips the current iteration of a for, while , or do-while loop. The unlabeled form skips to the end of the innermost loop's body and evaluates the boolean expression that controls the loop. The following program, ContinueDemo , steps through a String, counting the occurences of the letter "p". If the current character is not a p, the continue statement skips the rest of the loop and proceeds to the next character. If it is a "p", the program increments the letter count.
{code}class ContinueDemo {
public static void main(String[] args) {
String searchMe = "peter piper picked a peck of pickled peppers";
int max = searchMe.length();
int numPs = 0;
for (int i = 0; i < max; i++) {
//interested only in p's
if (searchMe.charAt(i) != 'p')
continue;
//process p's
numPs++;
System.out.println("Found " + numPs + " p's in the string.");
}{code}
Here is the output of this program:
Found 9 p's in the string.
To see this effect more clearly, try removing the continue statement and recompiling. When you run the program again, the count will be wrong, saying that it found 35 p's instead of 9.
A labeled continue statement skips the current iteration of an outer loop marked with the given label. The following example program, ContinueWithLabelDemo, uses nested loops to search for a substring within another string. Two nested loops are required: one to iterate over the substring and one to iterate over the string being searched. The following program, ContinueWithLabelDemo, uses the labeled form of continue to skip an iteration in the outer loop.
{code}class ContinueWithLabelDemo {
public static void main(String[] args) {
String searchMe = "Look for a substring in me";
String substring = "sub";
boolean foundIt = false;
int max = searchMe.length() - substring.length();
test:
for (int i = 0; i <= max; i++) {
int n = substring.length();
int j = i;
int k = 0;
while (n-- != 0) {
if (searchMe.charAt(j++)
!= substring.charAt(k++)) {
continue test;
foundIt = true;
break test;
System.out.println(foundIt ? "Found it" :
"Didn't find it");
}{code}
Here is the output from this program.
Found it"
Here are Woodie's thoughts........................................
1) With the first program I don't understand how the program counts the number of "p's". Like for example how it stores the number of "p's". Shouldn't it say:
if (searchMe.charAt(i) = 'p') then store it in some sort of containers??? 2) With the second program, I don't understand the test section. For example: Why does it have --? why does it have != after while and why does it have != after if?
while (n-- != 0)
                if (searchMe.charAt(j++) != substring.charAt(k++))
                    continue test;
            foundIt = true;
                 break test;Edited by: woodie_woodpeck on Nov 23, 2008 3:29 AM

Answer 1

Woodie, I think they're just silly "theoretical" examples... ergo don't worry too much not understanding them, coz they don't actually make a lot of sense... as you've allready pointed out there are other "more normal" control structures which achieve the same thing, and which in this case (in my humble opinion) would make for clearer, more concise, more maintainable code.
All you need to know about continue is "it means go back to the top of the loop"... If you're not comfortable using "continue" then don't.
There's more than one way to do it.
  public static void main(String[] args) {
    try {
      final String s = "peter piper picked a peck of pickled peppers";
      int count = 0;
      for ( char c : s.toStringArray() ) {
        if (c=='p') count++;
      System.out.println("There are "+count+ " p's in '"+s+"'");
    } catch (Exception e) {
      e.printStackTrace();
  }Having said all that... I did use continue in anger the other day... I was reading Geometries from a shape file... the reader was throwing an ArrayIndexOutOfBoundsException given an "empty Feature" (ie a feature with the geospatial presence)... All I did was catch the exception and continue trying to read the new feature... the alternative would have been to rewrite the control logic of the whole reader loop... quick, simple effective... but I don't routinely build continue statements into new code... just a matter of personal taste.
Cheers. Keith.