Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Just as <code>enum</code> is recommended by <em>Effective Java 2nd Edition</em> to implement singleton, this solution also uses <code>enum</code> to implement... quadrupleton?</p> <pre><code>import java.util.*; public enum RoundRobin { EENIE, MEENIE, MINY, MO; private final static List&lt;RoundRobin&gt; values = Collections.unmodifiableList(Arrays.asList(values())); // cache it instead of creating new array every time with values() private final static int N = values.size(); private static int counter = -1; public static RoundRobin nextInstance() { counter = (counter + 1) % N; // % is the remainder operator return values.get(counter); } public static void main(String[] args) { for (int i = 0; i &lt; 10; i++) { System.out.println(RoundRobin.nextInstance()); } // EENIE, MEENIE, MINY, MO, EENIE, MEENIE, MINY, MO, ... } } </code></pre> <p>Extending this to quintupleton is self-explanatory.</p> <h3>See also</h3> <ul> <li><em>Effective Java 2nd Edition, Enforce singleton property with a private constructor or an enum type</em> <blockquote> <p>As of release 1.5., there is a third approach to implementing singletons. Simply make an enum type with one element. This approach is functionally equivalent to the public field approach, except that it is more concise, provides serialization mechanism for free, and provides an ironclad guarantee against multiple instantiation, even in the face of sophisticated serialization or reflection attacks. While this approach has yet to be widely adopted, <strong>a single-element enum type is the best way to implement a singleton</strong>.</p> </blockquote></li> </ul> <h3>Related questions</h3> <ul> <li><a href="https://stackoverflow.com/questions/70689/efficient-way-to-implement-singleton-pattern-in-java">Efficient way to implement singleton pattern in Java</a></li> </ul>
    singulars
    1. This table or related slice is empty.
    1. POWrite a java class to have only five instance of it created
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USCommunity
    1. USpolygenelubricants
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POWrite a java class to have only five instance of it created
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COPresumably this pattern is not threadsafe?
      singulars
      1. PO
      1. USmchr
    2. CO@mchr: You presume wrong. Enum is ironclad guaranteed by the language itself to have tightly controlled instantiation, allowing you to use `==` instead of `equals` should you choose to do so.
      singulars
      1. PO
      1. USpolygenelubricants
    3. COSorry I should have been much clearer about which part I considered threadsafe :). public static RoundRobin nextInstance() This method is doing unsynchronized access to an int. Surely multiple threads could end up selecting the same instance.
      singulars
      1. PO
      1. USmchr
 

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