Button switch Arduino to Processing: serial output giving null - arduino

Question

I am trying to use a button switch in Arduino to trigger a visual display in Processing. I used "HIGH" and "LOW" to identify whether the button is pressed.
However, my code is constantly giving null instead of giving "HIGH" or "LOW" depending on the button state. I think this is pretty basic but I'm just quite lost. Any helps or comments would be appreciated!
Below is my code for Arduino and Processing respectively.
const int buttonPin = 2;
const int LEDPin = 13;
int buttonState = 0;
void setup() {
pinMode(buttonPin, INPUT);
pinMode(LEDPin, OUTPUT);
Serial.begin(9600);
}
void loop() {
int analogValue = analogRead(A0)/4;
Serial.write(analogValue);
buttonState = digitalRead(buttonPin);
if (buttonState == HIGH) {
Serial.write(HIGH);
digitalWrite(LEDPin, HIGH);
} else {
Serial.write(LOW);
digitalWrite(LEDPin, LOW);
}
delay(100);
}
Processing code:
import processing.serial.*;
Serial myPort;
String val;
void setup() {
size(400,400);
String portName = Serial.list()[1];
myPort = new Serial(this, portName, 9600);
}
void draw() {
if (myPort.available() > 0) {
val = myPort.readStringUntil('\n');
println(val);
if (val == "HIGH") {
background(127,0,0);
}
if (val == "LOW") {
background(144, 26, 251);
}
}
}

Answer 1

write()
Writes binary data to the serial port. This data is sent as a byte or series of bytes.
Serial.write(str)
str: a string to send as a series of bytes
So when you use write HIGH and LOW in Serial.write, it will be send as a series of bytes. Edit your processing part to handle the incoming bytes. Just as follows :
import processing.serial.*;
Serial myPort;
String val;
int len; //length of byte array
void setup() {
size(400,400);
String portName = Serial.list()[1];
myPort = new Serial(this, portName, 9600);
}
void draw() {
if ((len=myPort.available()) > 0) {
for(i=0;i<len;i++)
myByteArray=myPort.read();
String val = String(myByteArray);
println(val);
if (val == "HIGH") {
background(127,0,0);
}
if (val == "LOW") {
background(144, 26, 251);
}
}
}

Answer 2

just change your buttonState variable type from integer to boolean, and then use
if(buttonState) {
Serial.println("HIGH");
}
else {
Serial.println("LOW");
}

Answer 3

In Arduino, HIGH and LOW are defined as 1 and 0.
By executing Serial.write(HIGH); and Serial.write(LOW); you are just sending a single byte 1 or 0.
But according to your Processing code, you are expecting Serial.write(HIGH); to send 'H', 'I', 'G', 'H' and '\n' characters.
In your Arduino code, you need to replace Serial.write(HIGH); and Serial.write(LOW); with Serial.print("HIGH\n"); and Serial.print("LOW\n");.