Why I need to add some delay while making concurrent request in streaming gRPC? (Java) to get output - asynchronous

Question

#Test
public void testType() throws InterruptedException {
Integer num = 15;
String name = "Sahil";
Float percentage = 96.7f;
DOB dob = DOB.newBuilder().setDay(20).setMonth(8).setYear(2022).build();
ArrayList<Object> objects = new ArrayList<>(Arrays.asList(num,name,percentage,dob));
TypeRequest.Builder builder = TypeRequest.newBuilder();
StreamObserver<TypeResponse> typeResponseStreamObserver = new StreamObserver<TypeResponse>() {
#Override
public void onNext(TypeResponse typeResponse) {
System.out.println(
"Type : " + typeResponse.getType()
);
}
#Override
public void onError(Throwable throwable) {
System.out.println("Error : "+throwable);
}
#Override
public void onCompleted() {
System.out.println("Finished all requests");
}
};
StreamObserver<TypeRequest> typeRequestStreamObserver = this.calculatorServiceStub.getType(typeResponseStreamObserver);
for(Object obj : objects){
if (obj instanceof Integer){
builder.setNum((Integer) obj);
typeRequestStreamObserver.onNext(builder.build());
} else if (obj instanceof String) {
builder.setName((String) obj);
typeRequestStreamObserver.onNext(builder.build());
} else if (obj instanceof Float) {
builder.setFNum((Float) obj);
typeRequestStreamObserver.onNext(builder.build());
} else if (obj instanceof DOB) {
builder.setDob((DOB) obj);
typeRequestStreamObserver.onNext(builder.build());
}
// --------------------------------------------
Thread.sleep(500);
// --------------------------------------------
}
typeRequestStreamObserver.onNext(builder.clearType().build());
typeRequestStreamObserver.onCompleted();
}
If I did not add any delay then the output console is just blank. Testing with tools like BloomRPC and Postman it works fine,
but for this I don't know why this is happening?
Any little help will be very helpful. I appreciate it.