problems with semantics and keywords.

I have the following lines of code with which I think there are a few problems to do with adding elements into a Vector:

     Vector v = new Vector();
     String s = "ABCD";
      for(int i = 0; i< s.length() i++)
        v.add(0, s.substring (i, i +1));

Please tell me what the problem with the v.add is and what would the final vector look like once the for loop has finished looping?

Also what is wrong with this lines of code:
    String x = " ";
    x += s.substring(2,5);

Does the += operator exist, and if so what does it do?
Does x need a variable type assinged to it?

Thanks for your help!
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I can't help with the first question, but the += statment should work with a string.
luinziAuthor Commented:
Ok thats great......but what does the += do exactly????????

as far as I know v.add() method is part of a collection of interfaces available for java 2. I think!!!
1. there's supposed to be a ; between s.length() and i++.

2. i don't see any prob with the add... just that this form of add started with JDK1.2 so make sure u're using that...
so if u dun want to use add use
insertElementAt(s.substring(....), 0) instead...

3. v will contain "D", "C", "B", "A" in that order...

4. substring's 2nd argument only takes up to s.length... which in this case is 4 (< 5) so the statement will throw an exception....

5. += means add to... s += a is the same as s = s + a
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Working code snippet with changes commented:

Vector v = new Vector();
String s = "ABCD";

// Added braces for clarity
// Added semicolon to separate second/third args
for (int i = 0; i < s.length(); i++) {
  // Changed .add(...) to insertElementAt(...) which is
  // supported
  v.insertElementAt(s.substring(i, i + 1),0);

// The following line was written to validate what went in
for (int i=0; i< s.length(); i++) {

String x = " ";
x += s.substring(2, 4); // Fixed the offset in substring so that it
                        // didn't go out of bounds

// Added to print out result to convince us it works
System.out.println("X: " + x);
Sorry lychee - my browser is set up for proxy and I didn't see your response first.
it's alright :>
Also just a further point luinzi, without meaning to sound picky as regards the previous answers, but usually it is best to avoid hardcoding the estimated lengths of strings...

String x = " ";
x += s.substring(2);

will get you all the characters in S from after second one to the last with no danger of going over the string length. For example,

"unhappy".substring(2) returns "happy"

Or instead use

String x = " ";
x += s.substring(2,s.length);

You could get really picky and make sure that there are actually at least two characters in the string but that is a level of fault tolerance I don't think matters for you here.

There are also a range of command similar to


inherited from C/C++ that are retained in Java.

Such as -=. For example:

  a -= 1;

I bet you can guess the rest...

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luinziAuthor Commented:
Thank you!
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