Adding methods to exists class in android

Question

I'm looking for a way to add some methods into exists class like this:

String s = "";
s.doSomething();

In objective C, I can use category to do this.

@interface NSString( Stuff)
-(void)doSomething();
@end

Is android has something like that? Or another hack?

Update: Actually, I got this problem: I use a class (not final) from jar file (so, I can't touch its source code). Then I want to add methods( or something like that) into this class without using inheritance. For example:

 public class Provider{
       // many methods and fields go here...
       public String getName(){}
 }

All I want to do is:

 provider.print(); //that call getName() method;

I also tried proxy pattern, it worked, but I don't like that way (because it like a wrapper class, I must store an object with many fields and methods to use only one method):

 public class ProxyProvider{
       Provider provider;
       public ProxyProvider(Provider provider){
           this.provider = provider;
       }
       public void print(){
           String name = provider.getName();
           //do something
       }
 }

Is there any way to solve that?

Answer 1

You could create a utility class with static methods:

public final class ProviderUtils {

    private ProviderUtils() {} // not instantiable, it is a utility class

    public static void print(Provider provider) {
        String name = provider.getName();
        // print the name
    }
}

In your code, you can then call it:

Provider p = new Provider(...);
ProviderUtils.print(p);

And if that class only has one print method, you can maybe call it ProviderPrinter instead of ProviderUtils.

In the end you don't have thousands of possibilities - you can:

• extend the class and whatever method you need in the sub class => you said you don't want that
• modify the source code of the class and recompile your own version of the jar
• wrap the class in a wrapper that adds the methods you need (your ProxyProvider example)
• put the methods you need in a static utility class (what I proposed above)
• modify the class at runtime and add a method, but that's a complicated path because you need to play with classloaders.

Answer 2

It is not possible, however, there is a java like DSL available called Xtend that can be used as a compelling replacement for JAVA that might be work looking at which supports extension methods like this.

http://www.eclipse.org/xtend/

DISCLAIMER: I am in no way associated to this I am just an avid user of the core technology that was used to create xtend called xtext. I have considered using xtend on an Android project