Java Jaeger control span activate based on flags

Question

I'm just beginner with Jaeger implementation and want to know how can I controll if span can be instantiated based on flag=true

Below, is sample logic I'm trying to put behind the flag condition?

try (Scope scope = tracer.scopeManager().activate(span, true)) {
    System.out.println("The code will come here");
    for (int i = 0; i < 100; i++) {
        System.out.println("code working...");
    }
} finally {
    span.finish();
}

if instantiating in other class

if (FLAG) {
        tracer = TryFeatureFlag.initTracer();
        span = tracer.buildSpan("inside-timepass").start();
    }