Send only String variable from Java to Arduino and reverse

Question

1. Need another new libraries.
2. This is the code for java.
3. My porposes are sending from java to arduino variable like this String = "hello" But nothing Its happiens.

Java code:

package j;
import arduino.*;
public class K {
 public static void main(String[] args) {
 Arduino obj = new Arduino("COM4", 115200);
 obj.openConnection();
 String MyStr="hello";
 System.out.println(MyStr); 
 obj.serialWrite(MyStr); 
 obj.closeConnection(); 
 
 }
}

This is minimal arduino code fragment: It's working if from console send "hello" ,"1","2", "help" String vars.

Arduino code:

int RR=255;
int GG=255;
int BB=255;
String MyStr="0";
void setup() {
 Serial.begin(115200);
 Serial.setTimeout(0);
}
void loop() {
 //L0();
 
 
 while (Serial.available()>0) { //if data has been written to the Serial stream
 //data0=Serial.read();
 String MyStr = Serial.readString();
 if ((MyStr).equals("1")){
 Serial.println (MyStr);
 RR=200;GG=0;BB=0;
 }
 
 
 if (MyStr == ("2")) {
 Serial.println (MyStr);
 RR=0;GG=0;BB=255;
 }
 if (MyStr == "hello") {
 Serial.println (MyStr);
 RR=0;GG=244;BB=0;
 }
 
 if (MyStr == "help") {
 Serial.println (MyStr);
 RR=225;GG=255;BB=255;
 }
 
 }
 
}

• Robert: Does it work if you send the same string using the same COM settings using e.g. a terminal program like Putty?
• Aurimas V.: i think you never declared MyStr.
• aled: Please provide a real minimal reproducible example.
• Juraj: Arduino resets on a new USB connection and waits in the bootloader a few seconds
• g00se: if ("1".equals(data0)) is what you need. Duplicate