test.pde

void draw() {
  if (currentStage==null) {
    currentStage = (Stage) q.poll();
    println("use Stage="+currentStage.name);
  }
  if (currentStage==null) {
  }
  else {
    if (currentStage.status == StateType.INITIAL) {
      callMethod(currentStage.initMethod);
    }
    else if (currentStage.status == StateType.FINAL) {
      currentStage.status = StateType.INITIAL;
      q.offer(currentStage);
      currentStage=null;
    }
    else {
      if (currentStage.checkMethod!=null) {
        callMethod(currentStage.checkMethod);
      }
      if (currentStage.loopMethod!=null) {
        callMethod(currentStage.loopMethod);
      }
    }
  }
}

int a = 0;
a = (currentStage==null) ? 1: 0;
switch(a)
{
case 1:
currentStage = (Stage) q.poll();
println("use Stage="+currentStage.name);
}