If I have a String "Hello" and I know it is a name of a class, how to use it to create a object?

[fAnSKyer]

If I have a String "Hello" and I know it is a name of a class, how to
use the string to create a object?

Thanks, fAn

 

[Andrew Thompson]

If I have a String "Hello" and I know it is a name of a class, how to
use the string to create a object?

Reflection. But what actual general problem are
you attempting to solve?

Using reflection in Java is generally considered a
poor hack (though some types of applications
need to use it extensively - like servers).

Andrew T.

 

[Thomas Schodt]

If I have a String "Hello" and I know it is a name of a class, how to
use the string to create a object?

You mean like

String classname = "Hello";
Object o = Class.forName(classname).newInstance();

<http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Class.html#forName(java.lang.String)>
<http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Class.html#newInstance()>

 

[fAnSKyer]

Thanks a lot, also to Andrew T.

You mean like

String classname = "Hello";
Object o = Class.forName(classname).newInstance();

<http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Class.html#forName(java.lang.String)>
<http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Class.html#newInstance()>

 

[fAnSKyer]

A following question,
It can run, but IF the class "Hello" have a method get();

using o.get() is wrong. Because it is a Object, not a Class. How to
solve then?


Thanks a lot
Fans.

Thomas Schodt 写é“：

 

[Dijon Yu]

A following question,
It can run, but IF the class "Hello" have a method get();

using o.get() is wrong. Because it is a Object, not a Class. How to
solve then?

If method get() is not a static method, you must create a instance of
Hello class, you use Object o =
Class.forName(classname).newInstance();
like Thomas Schodt write
Dijon Yu

 

[Thomas Schodt]

A following question,
It can run, but IF the class "Hello" have a method get();

using o.get() is wrong. Because it is a Object, not a Class. How to
solve then?

You either need to know about the class (which defeats the purpose)
or it needs to implement a known interface


interface KnownInterface {
Object get();
}

class UnknownClass implements KnownInterface {
Object get() {
// ...
}
}


String classname = "UnknownHello";
Object o = Class.forName(classname).newInstance();
KnownInterface ki = (KnownInterface)o;
Object ret = ki.get();


or you need to get serious with reflection - read
<http://java.sun.com/j2se/1.4.2/docs/api/java/lang/reflect/package-summary.html>

 

[fAnSKyer]

Thanks a lot.

What if KnownInterface is also a String and I need use this String to
do the following steps?
Still need help.

Thanks, fAns.
Thomas Schodt 写é“：

 

[Thomas Schodt]

What if KnownInterface is also a String

Then it is not a known interface.

Still need help.

you need to get serious with reflection - read
<http://java.sun.com/j2se/1.4.2/docs/api/java/lang/reflect/package-summary.html>

There seems to be a number of threads around on this.
Read them.

 

[su_dang]

A following question,
It can run, but IF the class "Hello" have a method get();

using o.get() is wrong. Because it is a Object, not a Class. How to
solve then?


Thanks a lot
Fans.

Thomas Schodt 写é“：

Using reflection, you can obtain an object of the class Method which
can be used to invoke the method you want.

 

[fAnSKyer]

thanks and those who helped me

Using reflection, you can obtain an object of the class Method which
can be used to invoke the method you want.