static variable lose its value
- by user542719
I have helper class with this static variable that is used for passing data between two classes.
public class Helper{
    public static  String paramDriveMod;//this is the static variable in first calss
}
this variable is used in following  second class mathod
public void USB_HandleMessage(char []USB_RXBuffer){
 int type=USB_RXBuffer[2];
 MESSAGES ms=MESSAGES.values()[type];
 switch(ms)
   {
    case READ_PARAMETER_VALUE:  // read parameter values
                switch(prm){
                    case PARAMETER_DRIVE_MODE:  // paramet drive mode
                       Helper.paramDriveMod =(Integer.toString(((USB_RXBuffer[4]<< 8)&0xff00)));
                       System.out.println(Helper.paramDriveMod+"drive mode is selectd ");//here it shows the value that I need.
..........}}//let say end switch and method
and the following is an third class method use the above class method
public   void buttonSwitch(int value) throws InterruptedException{
boolean bool=true;
int c=0;
int delay=(int) Math.random();
  while(bool){
  int param=3;
  PARAMETERS prm=PARAMETERS.values()[param];
switch(value){
    case 0: value=1;
            while(c<5){
            Thread.sleep(delay);                
            protocol.onSending(3,prm.PARAMETER_DRIVE_MODE.ordinal(),dataToRead,dataToRead.length);//read drive mode
            System.out.println(Helper.paramDriveMod+"  drive mode is ..........in wile loop");//here it shows null value
}}//let say end switch and method           
what is the reason that this variable lose its value?