loops - Java: How do I return user to main menu if user input is not a single alphabetic lowercase letter? -

i'm trying run program allow user input both char keycharacter , string thestring. then, using these inputs, mask keycharacter if occurs in thestring "$", remove keycharacter thestring, , finally, count number of times keycharacter occurs in thestring altogether.

every method working fine, except method getkeycharacter user has input char: user can enter single letter (e.g. q, or z).

if user enters other single letter (which can word, phrase, sentence, special character # or $, blank space or tabs, or pressing enter), program returns user original question asks keycharacter user. should continue looping original question until user enters valid input.

since i'm still beginner java , loops weakness far, part causing me lot of trouble. know should using while loop, logic behind nested loops confusing me.

from searching possible solutions, know there these things called regex , try-catch exception issue, since haven't gone on explicitly in class, i'd prefer not deal now. thank you.

here's paste of code:

import java.util.*;  public class foothill {      // main method     public static void main (string[] args) {         char keycharacter = getkeycharacter();         string thestring = getstring();             maskcharacter(thestring, keycharacter);         countkey(thestring, keycharacter);         removecharacter(thestring, keycharacter);     }      // keycharacter     public static char getkeycharacter() {         scanner inputstream = new scanner(system.in);         boolean stop = false;         string firstprompt, strkeycharacter;         char keycharacter = ' ';          while (stop != true) {             firstprompt = "please enter single character act key: ";             system.out.print(firstprompt);             strkeycharacter = inputstream.nextline();               while (strkeycharacter.length() != 1) {                 firstprompt = "please enter single character act key: ";                 system.out.print(firstprompt);                 strkeycharacter = inputstream.nextline();             }              keycharacter = strkeycharacter.charat(0);              while (strkeycharacter.length() == 1) {                 firstprompt = "please enter single character act key: ";                 system.out.print(firstprompt);                 strkeycharacter = inputstream.nextline();                 if (keycharacter == 'a' || keycharacter == 'b' || keycharacter == 'c' || keycharacter == 'd'                    || keycharacter == 'e' || keycharacter == 'f' || keycharacter == 'g' || keycharacter == 'h'                   || keycharacter == 'i' || keycharacter == 'j' || keycharacter == 'k' || keycharacter == 'l'                   || keycharacter == 'm' || keycharacter == 'n' || keycharacter == 'o' || keycharacter == 'p'                   || keycharacter == 'q' || keycharacter == 'r' || keycharacter == 's' || keycharacter == 't'                   || keycharacter == 'u' || keycharacter == 'v' || keycharacter == 'w' || keycharacter == 'x'                   || keycharacter == 'y' || keycharacter == 'z') {                     system.out.println("you entered: " + keycharacter + '\n');                     stop = true;                 } else {                     break;                 }             }         }         return keycharacter;     }      // declare final = 4 constant     public static final int minimumlength = 4;      // thestring     public static string getstring() {         scanner inputstream = new scanner(system.in);         string secondprompt, thestring;         {             secondprompt = "please enter phrase or sentence >= 4: ";             system.out.print(secondprompt);             thestring = inputstream.nextline();             system.out.print('\n');         } while (thestring.length() < minimumlength || thestring == null || thestring.length() == 0);         inputstream.close();         return thestring;     }      // mask keycharacter $     public static string maskcharacter(string thestring, char keycharacter) {         thestring = thestring.replace(keycharacter, '$');         system.out.println("string " + " '" + keycharacter + "' " + " masked.");         system.out.println(thestring + '\n');         return thestring;     }      // count number of times keycharacter occurs in thestring     public static void countkey(string thestring, char keycharacter) {         int countchar = 0;         (int chartimes = 0; chartimes < thestring.length(); chartimes++) {             if (thestring.charat(chartimes) == keycharacter) {                 countchar++;             }         }         system.out.println( "the key character occurs " + countchar + " times. \n");         return;     }      // remove keycharacter thestring     public static void removecharacter(string thestring, char keycharacter) {         thestring = thestring.replace(string.valueof(keycharacter), "");         system.out.println("string " + "'" + keycharacter + "' removed: ");         system.out.println(thestring);         return;     } } 

and here's paste of run (as can see, there serious debugging done in program):

please enter single character act key: f please enter single character act key: f entered: f  please enter single character act key: f entered: f  please enter single character act key: f entered: f  please enter single character act key: f entered: f  please enter single character act key:   // continues on forth... 

public static char getkeycharacter(){      scanner inputstream = new scanner(system.in);     boolean stop = false;     string firstprompt, strkeycharacter;     char keycharacter = ' ';      while(!stop){          firstprompt = "please enter single character act key: ";         system.out.println(firstprompt);         strkeycharacter = inputstream.nextline();          //check if input contains 1 character         boolean issinglechar = (strkeycharacter.length() == 1);         //check if input character within ascii code of 97 (a) 122 (z)         boolean isvalidchar =                  strkeycharacter.charat(0) >= 97 &&                 strkeycharacter.charat(0) <= 122;          if(issinglechar && isvalidchar){             keycharacter = strkeycharacter.charat(0);             stop = true;         }       }      return keycharacter; }