Java automatic Type Casting of any String

Question

is there a way to cast any String automatically to its primitive data type in Java? For example having a List with 10 Strings:

string1 = "1234"
string2 = "12.34"
string3 = "String"
string4 = "0.53"
...

I would like to hand them all in a method and get the value back converted in its correct data type (Float, Integer, String):

int1 = 1234
float1 = 12.34
string1 = "String"
float2 = 0.53
...

No. Nothing like that is built-in. You could write something close to it, but it would be ugly, hack-y and fragile. — Elliott Frisch
– Elliott Frisch, Commented Jul 22, 2014 at 13:27
Is this for some kind of serialisation? If so then there are better ways of doing this in Java. — Bathsheba
– Bathsheba, Commented Jul 22, 2014 at 13:30
Once you've written your function, what is its return type going to be? — Jamie Cockburn
– Jamie Cockburn, Commented Jul 22, 2014 at 13:34
This would actually be a bad bad practice, as there might be more than one possible types while casting, You should only choose to parse back when you are sure what the resulting type should be a generic implementation just doesn't make sense to me. — Anirudh
– Anirudh, Commented Jul 22, 2014 at 13:47

Naveen Kumar Alone · Accepted Answer · 2014-07-22 13:41:08Z

1

Simply achieve by RegEx

String string = "/**Place your value*/";
if (string.matches("\\d+")) {
 int i = Integer.parseInt(string); 
} else if (string.matches("^([+-]?\\d*\\.?\\d*)$)")) {
 float f = Float.parseFloat(string); 
}

In the same manner you can parse double, long, ....

edited Jul 22, 2014 at 13:41

answered Jul 22, 2014 at 13:34

Naveen Kumar Alone

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6 Comments

user719662 Over a year ago

and how do you expect to distinguish float from int from String containing only digits etc using this technique?

Naveen Kumar Alone Over a year ago

by using regEx we can find its length or size, what ever we want. Come on man... ;)

user719662 Over a year ago

"Come on man" is hardly an answer to the question. Neither length nor size (what's the difference anyway?) tells you if it's a string, an integer or a floating point value.

Anirudh Over a year ago

Casting is only meant for he cases when you are sure about what the resulting type would be, a generic hack would only favor a particular case in case of ambiguity. There is a reason why Java doesn't have such a hack in built.

Anirudh Over a year ago

*the as it would clearly flout the "Strongly Typed" Paradigm of Java.

|

Basti · Accepted Answer · 2014-07-22 14:05:22Z

-1

There is no way to do that. you can test an object for its class by using instanceof

Object integerValue = 1234;
    Object doubleValue = 12.34;
    Object array = new String[] { "This", "is", "a", "Stringarray" };
    if (integerValue instanceof Integer) {
        System.out.println("it's an Integer! Classname: " + integerValue.getClass().getName()); // will be printed
    }
    if (doubleValue instanceof Double) {
        System.out.println("this one is a Double *___* Classname: " + doubleValue.getClass().getName()); // will be printed
    }
    if (array instanceof String) {
        System.out.println("Is it a String?");
    } else if (array instanceof String[]) {
        System.out.println("It's a Stringarray :O! Classname: " + array.getClass().getName()); // will be printed
    } else {
        System.out.println("Huh? Something went wrong here :D");
    }

edited Jul 22, 2014 at 14:05

user719662

answered Jul 22, 2014 at 13:38

Basti

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3 Comments

user719662 Over a year ago

OP asked how to convert String to other types - not how to distinguish Object types.

Basti Over a year ago

And i said "There is no way to do that"!!! As you might know, you can get a class by its name. Class.forName(className); You must give the complete package path instead of its name, but so you can get its class. You want to cast/convert String into another object? so you must make a new instance of the targetclass with the value of the string. this is how you do it

user719662 Over a year ago

Sadly, Basti, no, that's not how you do it - because your solution has Objects as an input, and OP explicitly stated that String is the input - you can't distinguish what String has inside by using instanceof, neither can you do that by casting String to Object, since the underlying instance would still be String. I see you're new to SO - please, instead of using multiple exclamation marks, try understanding the problem highlighted to you before dismissing it.

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