GWT: Synchronous Code Execution Using Callbacks

   @Override
    public void onModuleLoad() {
        startingHere();
    }

    void startingHere() {

        callback_To_Execute_And_Wait_Until_It_Returns(new Callback<Integer, String>() {

            @Override

            public void onFailure(final String reason) {

                System.out.println("callback failed because: " + reason);

            }

            @Override

            public void onSuccess(final Integer callback_return_value) {

                System.out.println("executed SECOND");

                System.out.println("callback result: " + callback_return_value);

                do_something_that_requires_the_callback_to_finish_successfully();

            }

        });

    }

    void callback_To_Execute_And_Wait_Until_It_Returns(final Callback<Integer, String> cb) {

        System.out.println("executed FIRST");

        do_something_that_has_to_finish_completely_before_the_callback_succeeds();

        final Integer this_might_be_the_return_value_of_the_callback = 42;

        cb.onSuccess(this_might_be_the_return_value_of_the_callback);

        System.out.println("==============");

    }

    void do_something_that_requires_the_callback_to_finish_successfully() {

        // ...

    }

    void do_something_that_has_to_finish_completely_before_the_callback_succeeds() {

        // ...

    }