Find one char in a String ? ? ?

[Douglas Braxton]

PROBLEM: String s (of indeterminate length) is passed to the method searchString(), the user is prompted to enter a one character search argument name s1. Object of the exercise is to count the number of times
s1 occurs within s, regardless of case h = H, H = h, as it were.
CAN ANYONE FIGURE OUT WHERE I AM GOING WRONG.
THIS IS THE METHOD CALL

String lineOne;     // strings entered from standard input
        String lineTwo;     
        String lineThree;  
        String lineFour;   
        String s;
        int z;
                
        // read in the entries
        lineOne    = JOptionPane.showInputDialog("String one:");
        lineTwo    = JOptionPane.showInputDialog("String two:");
        lineThree = JOptionPane.showInputDialog("String three:");
        lineFour   = JOptionPane.showInputDialog("String four:");
        s = lineOne + " " + lineTwo + " " + lineThree + " " + lineFour;
//=C=O=N=S=T=R=U=C=T=O=R=S        
        MyStrings my = new MyStrings( s );       
/* = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
 * searchChar() - search for a character within the string and count 
 * number of times it occurs
 *   
 */
        String s1 = JOptionPane.showInputDialog("Please enter a one character search argument: ");
        int charFound = my.searchChar(s1);

THIS IS THE METHOD

/* = = =  = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
 * searchChar() - black box to determine if char exists and how often
 *
 */ 
      //public int searchChar( char sChar )
      public int searchChar( String s1 )
       {
           int y = 0;
           //Character ch = new Character (sChar);
           char s2 =  s1.charAt( 0 ).toLowerCase( ) ;
           for ( int x = 0; x < s.length(); x++ ) 
           { 
                 if (  s.charAt( x ) == s2  || s.charAt( x ) == s2 )
                 {
                      y++;
                  }
           }      
           s2 = ( s1.charAt( 0 ).toUpperCase( ) );
           for ( int x = 0; x < s.length(); x++ ) 
           { 
                if (  s.charAt( x ) == s2  || s.charAt( x ) ==  s2 )
               {
                    y++;
                }
           } return y;
       }    

COMPILER MESSAGES
MyStrings.java [154:1] char cannot be dereferenced
char s2 = s1.charAt( 0 ).toLowerCase( ) ;
^
MyStrings.java [162:1] char cannot be dereferenced
s2 = ( s1.charAt( 0 ).toUpperCase( ) );
^
2 errors
Errors compiling MyStrings.
THANK YOU
doug

[chi Lin]

toLowerCase() & toUpperCase() can not be used on char returned
by s1.charAt(0);
try
Character.toUpperCase(s1.charAt(0));
Character.toLowerCase(s1.charAt(0));