refactoring java files

1 - In my java file foo.java, i've the following method:

public void doSomething(int a, int b){....}

This method is called in several java files of my project.

But now, i changed the method to the following:
public void doSomething(String a, String b){....}

and i want to update all the java files that call this method. Is there 
any quick way to refactor this change?

2 - Is there any refactoring tool for java in emacs?

Thanks,
Pedro