Databases
StackOverflow2013
Postsdbo
POAccess type of a generic in Java
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POAccess type of a generic in Java
    primarykey
    data
    text
    <p>I am trying to create a generic <code>Identifier</code> class which I would be able to use as follows:</p> <pre><code>public class TestGenericIdentifier { public static void main(String[] args) { Identifier&lt;Car&gt; carId = new Identifier&lt;&gt;(Car.IdentifierType.LICENSE_PLATE, "123 XYZ"); Identifier&lt;Person&gt; personId = new Identifier&lt;&gt;(Person.IdentifierType.SOCIAL_SECURITY, "123456"); System.out.println(carId); System.out.println(personId); } } </code></pre> <p>To get there, I started by creating an <code>Identifiable</code> interface:</p> <pre><code>public interface Identifiable&lt;T extends Enum&gt; {} </code></pre> <p>The idea being that a class that implements <code>Identifiable</code> needs to provide an enum <code>T</code> in its declaration which is the type of the first parameter of the <code>Identifier</code> constructor:</p> <pre><code>public class Identifier&lt;E extends Identifiable&lt;T&gt;&gt; { //does not compile public Identifier(T type, String value) { //some code } } </code></pre> <p>Now the code above does not compile as I can only use <code>Identifiable</code> (no parameter <code>T</code>) on the first line. If it worked I would be able to write the following two classes:</p> <pre><code>public class Car implements Identifiable&lt;Car.IdentifierType&gt;{ public enum IdentifierType { SERIAL_NUMBER, LICENSE_PLATE; } } public class Person implements Identifiable&lt;Person.IdentifierType&gt; { public enum IdentifierType { DATABASE_ID, SOCIAL_SECURITY; } } </code></pre> <p>Is there a way to do that using generics? <br> EDIT <br> One way is to compromise conciseness and keep compile-time type checking by doing:</p> <pre><code>public class Identifier&lt;T extends Enum&gt; { public Identifier(T type, String value) { } } </code></pre> <p>and the main function becomes:</p> <pre><code>Identifier&lt;Car.IdentifierType&gt; carId = new Identifier&lt;&gt;(Car.IdentifierType.LICENSE_PLATE, "123 XYZ"); Identifier&lt;Person.IdentifierType&gt; personId = new Identifier&lt;&gt;(Person.IdentifierType.SOCIAL_SECURITY, "123456"); </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USassylias
    1. USassylias
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POAccess type of a generic in Java
      1. USIvaylo Slavov
      1. VTFavorite
    2. VO
      singulars
      1. POAccess type of a generic in Java
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POAccess type of a generic in Java
      1. This table or related slice is empty.
      1. VTUpMod
    1. COI'm wondering why you need `Identifier` when you already have `Identifiable`.
      singulars
      1. POAccess type of a generic in Java
      1. USSteven Jeuris
    2. COBasically, an Identifiable is an object that gives you an enum of the types of identifiers. So a Car is identifiable by 2 different types of Identifier: SERIAL_NUMBER and LICENSE_PLATE.
      singulars
      1. POAccess type of a generic in Java
      1. USassylias
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload