For example, in Haxe I can create strictly typed variables:
var a:Float = 1.1; or var b:String = "hello" and also dynamic, if needed:
var d:Dynamic = true;
d = 22;
d = "hi";
How do I create this kind of variables in Java?
3 Answers
You can use Object
Object d = true;
d = 22;
d = "hi";
and you can use instanceof operator to check which type of data d is holding
Object d = true;
System.out.println(d instanceof Boolean); // true
d = 22;
d = "hi";
System.out.println(d instanceof Integer); // false
System.out.println(d instanceof String); // true
4 Comments
Lew Bloch
Use of
instanceof is a code smell, usually wafting from a flawed type analysis, and tends to create messy, bug-ridden code unless you know what you're doing.
Alex Byrth
@Lew, you're 100% correct. But the posted anwser replays the question.
Qaz
I would expect a dynamic variable to resolve usage at runtime, like C#'s
dynamic. That is, d.foo() would check at runtime that d has a foo method.Lew Bloch
There is a difference between run-time typing and dynamic typing. The
Object strategy described here creates more problems than it solves. You can do what's necessary using generics and run-time type tokens without sacrificing type orientation. This is not a good answer; in fact quite the opposite.
Dynamic typing is evil so Java eschewed it. Like Swift and C#, Java is strongly typed, which leads to safer and cleaner code. So give in to the Dark Side and put aside your rebel ways. Embrace the Force of type-oriented programming. You'll be the better for it.
7 Comments
Qaz
C# has
dynamic for dynamic typing. It's useful in some specific scenarios like JSON and interacting with COM.
shal
I agree, I avoid dynamic everywhere possible, I love strongly typed approach. I just needed to find out about it for some exceptional cases.
Lew Bloch
Java handles run-time typing for JSON just fine. You don't need dynamic typing at all for that, @chris
Lew Bloch
@shal please describe an "exceptional" case where you need dynamic typing and I'll show you how to solve it in Java with strong typing.
hmijail
I use an autogenerated JSON parser which aliases various JSON defs into a single type. C#'s
dynamic beautifully allows me to locally bypass the type system to deal with this. There are other solutions, but all of them are uglier and hackier. I wondered how would I have fixed this in Java, found this answer... and now I'm so glad I'm doing this in C#! Funny how limitations can be praised as features. That won't help Java improve. |
ObjectI think is what you are looking for.