Package no.digipost.util

Class JustA<T>

java.lang.Object

no.digipost.util.JustA<T>

Type Parameters:

T - The type of wrapped value. Should be an immutable value-type.

All Implemented Interfaces:

Serializable

public abstract class JustA<T>
extends Object
implements Serializable

Base class for creating simple "typed primitives" value classes. Typically for when you do not want to pass around simple Strings for values that has certain (business-) semantics in your application, even though a String does adequately express the value. By extending this class you do not have to implement the equals and hashcode. You would not refer to this class other than with an extends JustA<SomeType> decalaration in your class definition.

A common pattern for using this class would be:

 interface WithName {

   static JustAName of(String name) {
     return new JustAName(name);
   }

   final class JustAName extends JustA<String> implements WithName {

      private JustAName(String name) {
        super(name);
      }

      public String getName() {
        return theValue;
      }
    }


    String getName();
 }

This yields certain benefits, as you now have an interface (WithName) to use with your more complex domain types, which among other stuff, having a name. And you have a neat way to pass typed simple values using WithName.of("John Doe"). This especially enhances the readability of method invocations with multiple arguments, as you must explicitly state the semantics of each argument. Say a query of some sort:

db.findPerson(WithName.of("John Doe"), WithPhonenumber.of("555-98437"))

If the method parameters for some reason are refactored to switch places, the code invoking the method will not compile anymore, as the arguments are not given in the correct order even though they are really just Strings.

See Also:

• Serialized Form

Field Summary

Fields

Modifier and Type	Field	Description
protected final T	theValue

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	JustA(T theValue)
protected	JustA(T theValue, String description)
protected	JustA(T theValue, String description, SerializableFunction<? super T,String> valueToString)
protected	JustA(T theValue, SerializableFunction<? super T,String> valueToString)

Method Summary

Modifier and Type	Method	Description
final boolean	equals(Object obj)
final int	hashCode()
String	toString()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Details

theValue

protected final T theValue

Constructor Details

JustA

protected JustA(T theValue)

JustA

protected JustA(T theValue,
 String description)

JustA

protected JustA(T theValue,
 SerializableFunction<? super T,String> valueToString)

JustA

protected JustA(T theValue,
 String description,
 SerializableFunction<? super T,String> valueToString)

Method Details

equals

public final boolean equals(Object obj)

Overrides:

equals in class Object

hashCode

public final int hashCode()

Overrides:

hashCode in class Object

toString

public String toString()

Overrides:

toString in class Object