Create new object of class at runtime depending on a string

Question

Let's say I have 3 classes: GNP_US, GNP_China and GNP_India. I also have a "starter" class, which checks if there is a string in args[0]. This String is either "US","China" or "India". How am I able to dynamically create a new instance of a class depending on the string? I thought maybe something like this:

    public static void main(String[] args)
    {
      try
      {
        Class c=Class.forName("GNP_"+args[0]);
        Object o=c.newInstance();
      }
      catch(Exception e){......} 
    }

But since I have to cast my object into its correct class, I still have to use a lot of if-statements to cast my Objects depending on the "country"-string. Which leaves me with about the same lot of code lines, when I do it like this:

    [...]if(args[0].equals("US")
         {
           GNP_US us=new GNP_US();
         }

I hope you understand where I'm trying to go.

Thanks in Advance!

I've edited my answer to address the matter more correct

Beejay
– Beejay

2014-02-04 10:19:10 +00:00
Commented Feb 4, 2014 at 10:19 — Beejay
– Beejay, Commented Feb 4, 2014 at 10:19

ooxi · Accepted Answer · 2014-02-04 09:49:17Z

1

Use Class.newInstance for runtime instance creation.

answered Feb 4, 2014 at 9:49

ooxi

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WelcomeTo · Accepted Answer · 2014-02-04 09:51:14Z

1

Try this:

public static void main(String[] args) throws Exception {
        Class clazz = Class.forName("test.Demo");
        Demo demo = (Demo) clazz.newInstance();
    }

answered Feb 4, 2014 at 9:51

WelcomeTo

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Comments

Ankur Shanbhag · Accepted Answer · 2014-02-04 09:52:19Z

1

Try this:

public static void main(String a[]) {

    String className = str[0]; // Make sure the class name is correct
    Class c = null;
    try {
        c = Class.forName(className);
        // create instance at runtime
        Object o = c.newInstance();

    } catch (ClassNotFoundException exception) {
        // Handle
    } catch (InstantiationException exception) {
        // Handle
    } catch (IllegalAccessException exception) {
        // Handle
    }

}

Note: This will fail if the classname is incorrect. Please provide class-name along with the package hierarchy.

answered Feb 4, 2014 at 9:52

Ankur Shanbhag

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3 Comments

Beejay Over a year ago

This is pretty much what I found so far aswell, but I'm trying to avoid an awful long list of if-statements which I'll still have if I'll have to cast my objects to the correct class or am I missing something here?

Ankur Shanbhag Over a year ago

You have to down cast it to specific type to access class specific methods. Unless you cast it, I dont see any point in creating the instance.

Beejay Over a year ago

I've edited my answer accordingly. This might make my question more clear!

Sergey Bychkov · Accepted Answer · 2014-02-04 09:55:16Z

1

You may use Java Reflections Api. Something like that:

Class c = Class.forName("args[0]");
Object o = c.newInstance();

answered Feb 4, 2014 at 9:55

Sergey Bychkov

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1 Comment

Beejay Over a year ago

This does seem right, but after this I'd have to cast my Object statically which would contradict the whole purpose of dynamic, wouldn't it? ;)

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