boolean aON=false;
boolean bON=false;

void setup() {
  size(500,500);
  background(255); 
  smooth(); 
}

void draw() {
  if(aON) {
    drawLine1();
  }
  if(bON) {
    background(255);
  }
  if(aON = true) {
    aON = false;
  }
  if(bON = true) {
    bON = false;
  }
}

void keyTyped() {
  if(keyPressed) {
    if (key == '1') {
      aON = true;
    } else {
      aON = false;
    }
  }
  if(keyPressed) {
    if (key == '2') {
      bON = true;
    } else {
      bON = false;
    }
  }
}

void drawLine1() {
  int x2=(int)random(500);
  int y2=(int)random(500);
  stroke(0);
  line(250,250,x2,y2);
}