instantiate class from string

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sarath - 29 Apr 2005 06:47 GMT

1.

I have a method,

public void something(String fullyQualifiedClassName)
{
}

the parameter passed to the method is a fully qualifed class name for a
class. I have to instantiate that very same class inside the method.
how can u do it ?

2.
Why string is immutable which is an additional overhead ?

thanks in advance

sarath

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Peter MacMillan - 29 Apr 2005 07:39 GMT

> 1.
>
[quoted text clipped - 7 lines]
> class. I have to instantiate that very same class inside the method.
> how can u do it ?

Here is an example that should get you started:

//--- CreateObject.java
public class CreateObject {

public static class SomeClass {
public void sayHello() {
System.out.println("Hello!");
}
}

public static Object createObject(String className)
throws ClassNotFoundException, InstantiationException,
IllegalAccessException {
return Class.forName(className).newInstance();
}

public static void main(String[] args) {
try {
Object o = createObject("CreateObject$SomeClass");
if (o instanceof SomeClass) {
((SomeClass) o).sayHello();
}
} catch (Exception e) {
System.out.println("Error: " + e.toString());
} // nb. you'll really want to catch the exceptions.
}
}
//---

> 2.
> Why string is immutable which is an additional overhead ?

There are a number of reasons why java.lang.String is immutable. Thread
safety is sometimes important. I think the API docs do a so-so job of
explaining why you might want an immutable String:

http://java.sun.com/j2se/1.5.0/docs/api/java/lang/String.html

> thanks in advance
>
> sarath

Signature

Peter MacMillan
e-mail/msn: peter@writeopen.com

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raghupulikkal@gmail.com - 29 Apr 2005 08:48 GMT

Thanks Peter.
That was one good explanation..

sarath

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instantiate class from string

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