Converting Lowercase string to Uppercase & Upper case string to Lower case

/* Here I'am converting lower case to Uppercase  */

string x='ajay';
string uppercase=x.touppercase();     //Converting string to Upper case
system.debug('uppercase ====>'+uppercase);

/* Here I'am converting Uppercase to lower case */
string y='SACHIN';
string Lowercase=y.tolowercase();
system.debug('lowercase====>'+Lowercase);