(Java) Get value of string loaded into dynamic-type object?

Question

I'm very new to Java (~10 days), so my code is probably pretty bad, but here's what I've got:

ArgsDataHolder argsData = new ArgsDataHolder();  // a class that holds two
                                                 // ArrayList's where each element
                                                 // representing key/value args
Class thisArgClass;
String thisArgString;
Object thisArg;

for(int i=2; i< argsString.length; i++) {
    thisToken = argsString[i];
    thisArgClassString = getClassStringFromToken(thisToken).toLowerCase();
    System.out.println("thisArgClassString: " + thisArgClassString);
    thisArgClass = getClassFromClassString(thisArgClassString);

    // find closing tag; concatenate middle
    Integer j = new Integer(i+1);
    thisArgString = getArgValue(argsString, j, "</" + thisArgClassString + ">");

    thisArg = thisArgClass.newInstance();
    thisArg = thisArgClass.valueOf(thisArgString);
    argsData.append(thisArg, thisArgClass);
}

The user basically has to input a set of key/value arguments into the command prompt in this format: <class>value</class>, e.g. <int>62</int>. Using this example, thisArgClass would be equal to Integer.class, thisArgString would be a string that read "62", and thisArg would be an instance of Integer that is equal to 62.

I tried thisArg.valueOf(thisArgString), but I guess valueOf(<String>) is only a method of certain subclasses of Object. For whatever reason, I can't seem to be able to cast thisArg to thisArgClass (like so: thisArg = (thisArgClass)thisArgClass.newInstance();, at which point valueOf(<String>) should become accessible.

There's got to be a nice, clean way of doing this, but it is beyond my abilities at this point. How can I get the value of the string loaded into a dynamically-typed object (Integer, Long, Float, Double, String, Character, Boolean, etc.)? Or am I just overthinking this, and Java will do the conversion for me? :confused:

[Off-topic]: Classes should be named using UppercaseStartingCamelCase (so argsDataHolder should be ArgsDataHolder). — Greg Kopff
– Greg Kopff, Commented Jun 4, 2012 at 4:17
A static method on which class? The various "boxed" objects (Integer, Long, Boolean) etc have valueOf() methods, but they're (a) static and (b) don't have a common ancestory. You'd have to reflectively call the method, rather than thisArgClass.valueOf(thisArgString). — Greg Kopff
– Greg Kopff, Commented Jun 4, 2012 at 4:21
You have two successive lines that assign a value to thisArg -- is that a "typo"? — Greg Kopff
– Greg Kopff, Commented Jun 4, 2012 at 4:22
Michael, If you know that variable type of the right side is an Integer, Long, Float, Double, String and whatever, thisArg = (String) thisArgClass will work. If you dont know then you have to use instanceOf -- java-samples.com/showtutorial.php?tutorialid=332 — vajapravin
– vajapravin, Commented Jun 4, 2012 at 4:23
@vajapravin: can you write that up as an answer (with more detail), because I don't understand your comment. — Greg Kopff
– Greg Kopff, Commented Jun 4, 2012 at 4:24

UVM · Accepted Answer · 2012-06-04 04:29:56Z

1

I can't seem to be able to cast thisArg to thisArgClass (like so: thisArg = (thisArgClass)thisArgClass.newInstance();,

This will not work like this as you need to initialize thisArgClass first.This will produce compile time error. Change the code something like this:

Class thisArgClass = null;
try {
    Object thisArg = thisArgClass.newInstance();
} catch (InstantiationException ex) {
    Logger.getLogger(Test3.class.getName()).log(Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
    Logger.getLogger(Test3.class.getName()).log(Level.SEVERE, null, ex);
}

Hope this will help you.

answered Jun 4, 2012 at 4:29

UVM

9,9247 gold badges43 silver badges66 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

TimFoolery Over a year ago

Sorry... the ... in the code was supposed to represent the parts where variables are assigned values. I'll add that in to make that more clear.

UVM Over a year ago

@Michael OK so that it will be more clear to others as well and chances of getting answers will be more.

Jim Garrison · Accepted Answer · 2012-06-04 04:44:00Z

1

There are several things wrong here. I'll assume that thisArgClass has been set correctly; for your example it would contain Integer.class. In order to invoke newInstance() on a Class object, the class must have a no-arg constructor. Class Integer does not have such a constructor, so you have to invoke one of the existing constructors using a more roundabout method:

Constructor<Object> c = thisArgClass.getConstructor(String.class);
Object i = c.newInstance(thisArgString);

Since you don't know the actual type of the object until runtime you must use <Object> and cast the result to the desired type before using the value.

answered Jun 4, 2012 at 4:44

Jim Garrison

87k20 gold badges162 silver badges197 bronze badges

1 Comment

TimFoolery Over a year ago

I tried something like this earlier, but it didn't work. I think I passed getConstructor() the wrong parameter type. Will try your solution here in a sec.

Collectives™ on Stack Overflow

(Java) Get value of string loaded into dynamic-type object?

2 Answers 2

2 Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related