sandbox/src/main/java/org/robolectric/internal/bytecode/ClassInstrumentor.java
private void addRoboInitMethod(MutableClass mutableClass) {
    MethodNode initMethodNode = new MethodNode(Opcodes.ACC_PROTECTED, ROBO_INIT_METHOD_NAME, "()V", null, null);
    RobolectricGeneratorAdapter generator = new RobolectricGeneratorAdapter(initMethodNode);
    Label alreadyInitialized = new Label();
    generator.loadThis();                                         // this
    generator.getField(mutableClass.classType, ShadowConstants.CLASS_HANDLER_DATA_FIELD_NAME, OBJECT_TYPE);  // contents of __robo_data__
    generator.ifNonNull(alreadyInitialized);
    generator.loadThis();                                         // this
    generator.loadThis();                                         // this, this
    writeCallToInitializing(mutableClass, generator);
    // this, __robo_data__
    generator.putField(mutableClass.classType, ShadowConstants.CLASS_HANDLER_DATA_FIELD_NAME, OBJECT_TYPE);
    generator.mark(alreadyInitialized);
    generator.returnValue();
    mutableClass.addMethod(initMethodNode);
  }
private void addRoboInitMethod(MutableClass mutableClass) {
    MethodNode initMethodNode = new MethodNode(Opcodes.ACC_PROTECTED, ROBO_INIT_METHOD_NAME, "()V", null, null);
    RobolectricGeneratorAdapter generator = new RobolectricGeneratorAdapter(initMethodNode);
    Label alreadyInitialized = new Label();
    generator.loadThis();                                         // this
    generator.getField(mutableClass.classType, ShadowConstants.CLASS_HANDLER_DATA_FIELD_NAME, OBJECT_TYPE);  // contents of __robo_data__
    generator.ifNonNull(alreadyInitialized);
    generator.loadThis();                                         // this
    generator.loadThis();                                         // this, this
    writeCallToInitializing(mutableClass, generator);
    // this, __robo_data__
    generator.putField(mutableClass.classType, ShadowConstants.CLASS_HANDLER_DATA_FIELD_NAME, OBJECT_TYPE);
    generator.mark(alreadyInitialized);
    generator.returnValue();
    mutableClass.addMethod(initMethodNode);
  }
Generates code like this:
```java
protected void $$robo$init() {
if (__robo_data__ == null) {
__robo_data__ = RobolectricInternals.initializing(this);
}
}
```