You can use globally defined constants by defining them inside a class and referencing themwithout instantiation.

 public class CONSTANT {

  public static final integer SUCCESS = 1;
  public static final integer FAILURE = -1;
  public static final integer NOTFOUND = 0;

}

Since the members of the class are defined as "static", there is no need to instantiate the class. To use a constant, simply use CONSTANT.[constant name]

 if (myMethod()==CONSTANT.SUCCESS) {
   ...;
}
else {
   ...;
}