How can I create an utility class

Question

I want to create a class with utility methods  for example  public class Util       public static void f  int i            public static int g  int i  int j             Which is the best method to create an utility class   Should I use a private constructor   Should I make the utility class for abstract class   Should I do nothing

User · Answer

Making a class abstract sends a message to the readers of your code that you want users of your abstract class to subclass it  However  this is not what you want then to do  a utility class should not be subclassed   Therefore  adding a private constructor is a better choice here  You should also make the class final to disallow subclassing of your utility class

User · Answer

For a completely stateless utility class in Java  I suggest the class be declared public and final  and have a private constructor to prevent instantiation  The final keyword prevents sub-classing and can improve efficiency at runtime   The class should contain all static methods and should not be declared abstract  as that would imply the class is not concrete and has to be implemented in some way    The class should be given a name that corresponds to its set of provided utilities  or  Util  if the class is to provide a wide range of uncategorized utilities    The class should not contain a nested class unless the nested class is to be a utility class as well  though this practice is potentially complex and hurts readability    Methods in the class should have appropriate names   Methods only used by the class itself should be private   The class should not have any non-final non-static class fields   The class can also be statically imported by other classes to improve code readability  this depends on the complexity of the project however    Example   public final class ExampleUtilities          Example Utility method     public static int foo int i  int j            int val             Do stuff          return val                Example Utility method overloaded     public static float foo float i  float j            float val             Do stuff          return val                Example Utility method calling private method     public static long bar int p            return hid p    hid p                 Example private method     private static long hid int i            return i   2   1            Perhaps most importantly of all  the documentation for each method should be precise and descriptive  Chances are methods from this class will be used very often and its good to have high quality documentation to complement the code

User · Answer

I would make the class final and every method would be static   So the class cannot be extended and the methods can be called by Classname methodName  If you add members  be sure that they work thread safe

User · Answer

According to Joshua Bloch  Effective Java   you should use private constructor which always throws exception  That will finally discourage user to create instance of util class   Marking class abstract is not recommended because is abstract suggests reader that class is designed for inheritance

[java] How can I create an utility class?

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