Convert JAVA Object to JSON

Hello everyone.

I have a problem with convert the object to json. I'm using gson to convert the java object to json string, but i got an error for this. Below is the describe

I have a class Bus

class Bus{
 private int id;
 private Route route;

  //setters and getters
}

class Route{
 private int id;
 private List<Bus> listBus;
 
 //setters and getters
}

When i using gson to convert the bus object to json,

Gson gson = new Gson();
Bus bus = getABus();//get the bus
String json = gson.toJson(bus);

it generate this erros:

com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)

Could anyone know how to solve this problem please?

Thanks
Clark

Tags: Java, JSON