How to make a public module that can do some common functions in java?

Question

As asked in title, can I make a 'common' public Class and some public static foo() in it? Thanks!

Answer 1

short and easy: yes.

(but why haven't you simply tried it?)

Answer 2

A common way is to declare a utility class like this

package my.package;

public class Utility {

  private Utility() {
  }

  public static void foo() {
  }

}

If this class is on your classpath you always can do from everywhere

my.package.Utility.foo();

Answer 3

Yes, you can.

Where exactly do you see difficulties?

You can see the popular utility classes (such as StringUtils) in Jakarta Commons Lang for an example. Chances are that some of the very common function you are thinking of are already present in one of the Commons family of libraries.

Answer 4

yes...You can do it..

Answer 5

If you have the slightest doubt that your requirements may change, that you might need different versions of some methods for testing etc., then use an interface and a class, e.g.:

public interface Utils {
  public final static Utils INSTANCE = new MyUtils();
  Foo makeFoo();
  Bar transform(Foo foo) 
}

public class MyUtils implements Utils {
  public Foo makeFoo() { return new Foo(); }
  public Bar transform(Foo foo) { return new Bar(foo); } 
}

This makes it easy to switch to other implementations. And you will have less problems when you decide to start using a DI framework like Guice:

public class Client {
  private final Utils util;

  @Inject
  Client(Utils utils) {  //<--- Here Guice will inject for you what you specified
    this.utils = utils; 
  }  
}