Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>It's okay so long as you only want reference equality for your key - arrays don't implement "value equality" in the way that you'd probably want. For example:</p> <pre><code>byte[] array1 = new byte[1]; byte[] array2 = new byte[1]; System.out.println(array1.equals(array2)); System.out.println(array1.hashCode()); System.out.println(array2.hashCode()); </code></pre> <p>prints something like:</p> <pre><code>false 1671711 11394033 </code></pre> <p>(The actual numbers are irrelevant; the fact that they're different is important.)</p> <p>Assuming you <em>actually</em> want equality, I suggest you create your own wrapper which contains a <code>byte[]</code> and implements equality and hash code generation appropriately:</p> <pre><code>public final class ByteArrayWrapper { private final byte[] data; public ByteArrayWrapper(byte[] data) { if (data == null) { throw new NullPointerException(); } this.data = data; } @Override public boolean equals(Object other) { if (!(other instanceof ByteArrayWrapper)) { return false; } return Arrays.equals(data, ((ByteArrayWrapper)other).data); } @Override public int hashCode() { return Arrays.hashCode(data); } } </code></pre> <p>Note that if you change the values within the byte array after using the <code>ByteArrayWrapper</code>, as a key in a <code>HashMap</code> (etc) you'll have problems looking up the key again... you could take a copy of the data in the <code>ByteArrayWrapper</code> constructor if you want, but obviously that will be a waste of performance if you know you <em>won't</em> be changing the contents of the byte array.</p> <p>EDIT: As mentioned in the comments, you could also use <code>ByteBuffer</code> for this (in particular, its <a href="http://docs.oracle.com/javase/7/docs/api/java/nio/ByteBuffer.html#wrap%28byte%5B%5D%29" rel="noreferrer"><code>ByteBuffer#wrap(byte[])</code></a> method). I don't know whether it's really the right thing, given all the extra abilities that <code>ByteBuffer</code>s have which you don't need, but it's an option.</p>
    singulars
    1. This table or related slice is empty.
    1. POUsing a byte array as Map key
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USseh
    1. USJon Skeet
    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. 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. CO@dfa: The "instanceof" test handles the null case.
      singulars
      1. PO
      1. USJon Skeet
    2. COA couple of other things you could add to the wrapper implementation: 1. Take a copy of the byte[] on construction therefore guaranteeing that the object is immutable, meaning there's no danger your key's hash code will change over time. 2. Pre-compute and store the hash code once (assuming speed is more important than storage overhead).
      singulars
      1. PO
      1. USAdamski
    3. CO@Adamski: I mention the possibility of copying at the end of the answer. In some cases it's the right thing to do, but not in others. I'd probably want to make it an option (possibly static methods instead of constructors - copyOf and wrapperAround). Note that *without* copying, you can change the underlying array until you first take the hash and check for equality, which could be useful in some situations.
      singulars
      1. PO
      1. USJon Skeet
 

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