I've just started working with Java 8 and I'm struggling with this code snippet:
paramsValues[idx++] = new ReplyMessage<JsonObject>() {
@Override
public void reply(JsonObject reply) {
message.reply(reply);
}
};
How to convert this to Lambda style?
If ReplyMessage is a functional interface, you could do
paramsValues[idx++] = reply -> message.reply(reply);
Here's a full example with stub implementations of the other classes in your question:
// Stub classes
class JsonObject { }
@FunctionalInterface
interface ReplyMessage<T> {
void reply(T jo);
}
class LambdaDemo {
public static void main(String args[]) {
// Dummy variables
ReplyMessage<JsonObject> message = new ReplyMessage<JsonObject>() {
public void reply(JsonObject jo) {}
};
ReplyMessage[] paramsValues = new ReplyMessage[5];
int idx = 0;
// Your code, lambdafied
paramsValues[idx++] = reply -> message.reply(reply);
// Or,
// paramsValues[idx++] = message::reply;
// But then you could perhaps do with just ...
// paramsValues[idx++] = message;
}
}
interface ReplyMessage<T>)
paramsValues[idx++] = (ReplyMessage<?>) ((JsonObject reply) -> message.reply(reply));
paramsValues[idx++] = (ReplyMessage<JsonObject>) reply -> message.reply(reply); as it’s only the target type that has to be included; there is no reason to make anything else more complicated compared to the original solution.Lambda expressions are only possible with Functional Interfaces (Interfaces with only one method, such as Runnable or ActionEvent)
If ReplyMessage is a functional interface, you can do:
paramsValues[idx++] = reply -> message.reply(reply);
Lambda expressions are formed in this pattern: parameters that the method should take, then -> then the method body
Here is the code of how ReplyMessage interface should look like:
@FunctionalInterface
interface ReplyMessage<T> {
void reply(T jo);
}
For more information, consider reading this.
@FunctionalInterface is optional. Also the restriction is not "only one method" but one abstract method. That's a rather big difference. I wonder what you mean by "take parameters". A function has parameters and takes arguments, if you meant that.paramValues[idx++] = reply -> message.reply(reply);
Or
paramValues[idx++] = reply -> {
return message.reply(reply);
}
It will work as long as ReplyMessage<JsonObject> is functional interface and paramValues is of type ReplyMessage<JsonObject>.
