Removing characters from a String (concats, substrings, etc)

Question

This has got me pretty stumped.
I'm creating a class which takes in a string and then returns the string without vowels and without even numbers. Vowels and even characters are considered "invalid." As an example:
Input: "hello 123"
Output: "hll 13"
The output is the "valid" form of the string.
Within my class, I have various methods set up, one of which determines if a particular character is "valid" or not, and it is working fine. My problem is that I can't figure out how to essentially "erase" the invalid characters from the string. I have been trying to work with substrings and the concat method, but I can't seem to get it to do what I want. I either get an OutOfBoundsException throw, or I get a cut-up string that just isn't quite right. One time I got the method to work with "hello" (it returned "hll") but when I modified the string the method stopped working again.
Here's what I have at the moment. It doesn't work properly for all strings, but it should give you an idea of where i'm going with it.
public String getValidString(){
          String valid = str;
          int start = 0;
          for(int i=0; i<=valid.length()-1; i++){
               if(isValid(valid.charAt(i))==false){
                         String sub1 = valid.substring(start, i);
                         while(isValid(valid.charAt(i))==false)
                              i++;
                         start=i;
                         String sub2 = valid.substring(i, valid.length()-1);
                         valid = sub1.concat(sub2);
          return valid;
     }So does anybody have any advice for me or know how I can get this to work?
Thanks a lot.

Answer 1

Thansk for the suggestions so far, but i'm not sure how to implement some of them into my program. I probably wasn't specific enough about what all I have.
I have two classes. One is NoVowelNoEven which contains the code for handling the string. The other is simply a test class, which has my main() method, used for running the program.
Here's my class and what's involved:
public class NoVowelNoEven {
//data fields
     private String str;
//constructors
     NoVowelNoEven(){
          str="hello";
     NoVowelNoEven(String string){
          str=string;
//methods
     public String getOriginal(){
          return str;
     public String getValidString(){
          String valid = str;
          int start = 0;
          for(int i=0; i<=valid.length()-1; i++){
               if(isValid(valid.charAt(i))==false){
                         String sub1 = valid.substring(start, i);
                         while(isValid(valid.charAt(i))==false)
                              i++;
                         start=i;
                         String sub2 = valid.substring(i, valid.length()-1);
                         valid = sub1.concat(sub2);
          return valid;
     public static int countValidChar(String string){
          int valid=string.length();
          for(int i=0; i<=string.length()-1; i++){
               if(isNumber(string.charAt(i))==false){
                    if((upperVowel(string.charAt(i))==true)||lowerVowel(string.charAt(i))){
                         valid--;}
               else if(even(string.charAt(i))==true)
                    valid--;
          return valid;
     private static boolean even(char num){
          boolean even=false;
          int test=(int)num-48;
          if(test%2==0)
               even=true;
          return even;
     private static boolean isNumber(char chara){
          boolean number=false;
          for(int i=0; i<=9; i++){
               if((int)chara-48==i){
                    number=true;
          return number;
     private static boolean isValid(char chara){
          boolean valid=true;
          if(isNumber(chara)==true){
               if(even(chara)==true)
                    valid=false;
          if((upperVowel(chara)==true)||(lowerVowel(chara)==true))
               valid=false;
          return valid;
}So in my test class i'd have something like this:
public class test {
public static void main(String[] args){
     NoVowelNoEven test1 = new NoVowelNoEven();
     NoVowelNoEven test2 = new NoVowelNoEven("hello 123");
     System.out.println(test1.getOriginal());
     //This prints hello   (default constructor string is "hello")
     System.out.println(test1.countValidChar(test1.getOriginal()));
     //This prints 3
     System.out.println(test1.getValidString());
     //This SHOULD print hll
}