Difference between revisions of "Coding Convention"

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Simantics coding conventions are gathered in this document. These rules apply to all ''org.simantics'' projects.
+
In this document I have gathered a set of very simple coding conventions. These apply to all ''org.simantics'' projects and are recommended for anyone developing with Java. I try to address some of the common mistakes that recur in a multi-developer project. A vast number of bugs can be back-tracked to failure of common understanding, a situation of mis-matching assumptions.
 +
 
 +
It is natural that our handiwork changes as we grow in experience. Sometimes a developer makes code where the rules or assumptions have changed along the way. For co-developers and future selves it can be a confusing trail. For the reader inconsistent convention leaves room for speculation, and can drive towards reaction-style-coding: guessing and fixing-on-error. Bad quality has a bad manner of propagating forwards, its common in projects with no rules at all. I'll get into more concrete specifics.
 +
 
 +
By following a common set of rules, hours are saved in avoided debugging. Quality is increased as developer minds can focus on the actual issues.
 +
 
 +
==Java Conventions==
 +
Pivotal documents for new java developers:
 +
* [http://www.oracle.com/technetwork/java/codeconv-138413.html Java Coding Style]
 +
* [http://www.oracle.com/technetwork/java/index-137868.html Java Comments Quick Reference]
 +
 
 +
 
  
 
==Argument Assumption==
 
==Argument Assumption==
Line 73: Line 84:
 
==Trust your assumptions==
 
==Trust your assumptions==
 
*'''You have a code of conduct - give it a chance.''' <br/>
 
*'''You have a code of conduct - give it a chance.''' <br/>
The callee can trust the caller.
+
The callee can trust the caller. Remember VM will do null checkings anyway.  
 
<div style="background: #f3fff3;">
 
<div style="background: #f3fff3;">
 
<syntaxhighlight lang="java">     
 
<syntaxhighlight lang="java">     
     Object deserialize(InputStream is) {
+
     BigInteger multiply(BigInteger a, BigInteger b) throw IOException {
         int x = is.read();
+
         return a.multiply(b);
        ...
 
        return result;
 
 
     }
 
     }
 
</syntaxhighlight>
 
</syntaxhighlight>
Line 88: Line 97:
 
<div style="background: #f3fff3;">
 
<div style="background: #f3fff3;">
 
<syntaxhighlight lang="java">     
 
<syntaxhighlight lang="java">     
     System.out.println( serialiser.deserialize( is ) );
+
     System.out.println( multiply(a, b) );
 
</syntaxhighlight>
 
</syntaxhighlight>
 
<br/>
 
<br/>
Line 94: Line 103:
 
<br/>
 
<br/>
  
There is no need to do redundant checking, especially at run-time.  
+
In most cases there is no good reason to do redundant checking, especially at run-time.  
 
<div style="background: #fff3f3;">
 
<div style="background: #fff3f3;">
 
<syntaxhighlight lang="java">     
 
<syntaxhighlight lang="java">     
     Object deserialize(InputStream is) {
+
     BigInteger multiply(BigInteger a, BigInteger b) throw IOException {
         if ( is == null ) throw IllegalArgumentException("Non-null argument");
+
         if ( a == null || b == null ) throw IllegalArgumentException("Non-null argument is expected");
         int x = is.read();
+
         return a.multiply(b);
        ...
 
        return result;
 
 
     }  
 
     }  
 
</syntaxhighlight>
 
</syntaxhighlight>
Line 109: Line 116:
 
<div style="background: #fff3f3;">
 
<div style="background: #fff3f3;">
 
<syntaxhighlight lang="java">     
 
<syntaxhighlight lang="java">     
     Object x = serializer.deserialize( is );
+
     Object x = multiply( a, b );
 
     if ( x != null ) System.out.println( x );
 
     if ( x != null ) System.out.println( x );
 
</syntaxhighlight>
 
</syntaxhighlight>
Line 116: Line 123:
 
<br/>
 
<br/>
  
Use assertions if you must. It some cases you can improve quality and debuggability.
+
Use assertions if you must. Checking does improve quality a bit and helps in early detection of problems, but is seldom needed if convention is followed. Assertion is not considered as run-time checking since they can be disabled from the VM.
 
<div style="background: #ffffea;">
 
<div style="background: #ffffea;">
 
<syntaxhighlight lang="java" style="background: #dfd;">     
 
<syntaxhighlight lang="java" style="background: #dfd;">     
     Object deserialize(InputStream is) {
+
     BigInteger multiply(BigInteger a, BigInteger b) {
         assert( is != null );
+
         assert( a != null && b != null );
         ...
+
         return a.multiply(b);
        return result;
 
 
     }
 
     }
 
</syntaxhighlight>
 
</syntaxhighlight>
Line 129: Line 135:
  
  
==Maintainment==
+
==Method migration==
These rules apply to code that is published and in wide use.
+
This rule applies to code that is published and in wide use.
  
 
*'''API doesn't change between minor releases.'''
 
*'''API doesn't change between minor releases.'''
In case of faulty design, old methods are preserved and are marked '''@deprecated'''. They can be removed in the next major version release.
+
In case of faulty design, old methods singature are preserved within the major version and marked '''@Deprecated'''. They can be removed in the next major release.
  
 
<div style="background: #fff3f3;">
 
<div style="background: #fff3f3;">
 
<syntaxhighlight lang="java">     
 
<syntaxhighlight lang="java">     
     @deprecated
+
     @Deprecated
 
     Object getValue(Object newValue);
 
     Object getValue(Object newValue);
 
</syntaxhighlight>
 
</syntaxhighlight>
Line 145: Line 151:
 
*'''Documentation is correct, the implementation is faulty.'''
 
*'''Documentation is correct, the implementation is faulty.'''
  
In case there is a mismatch between the documentation and the implementation, then the documentation prevails and the fault is in the implementation.
+
In situation where there is a mismatch between the documentation and the implementation, the documentation prevails and the fault is in the implementation.  
  
  
In this example the method returns an unexpected null.  
+
In this example there is problematic method that may return an unexpected null.  
 
<div style="background: #fff3f3;">
 
<div style="background: #fff3f3;">
 
<syntaxhighlight lang="java">     
 
<syntaxhighlight lang="java">     
Line 169: Line 175:
 
<br/>
 
<br/>
 
</div>
 
</div>
The '''documentation''' assumptions are unchanged and the '''implementation''' is corrected.  
+
The assumptions that can be derived from the '''documentation''' are left unchanged and the '''implementation''' is corrected.  
 
<div style="background: #f3fff3;">
 
<div style="background: #f3fff3;">
 
<syntaxhighlight lang="java">     
 
<syntaxhighlight lang="java">     
Line 178: Line 184:
 
     * @param is source stream
 
     * @param is source stream
 
     * @return the object
 
     * @return the object
     * @throws RuntimeSerializationException in case of IO problems
+
     * @throws RuntimeIOException in case of IO problems
 
     **/
 
     **/
     Object deserialize(InputStream is) throws RuntimeSerializationException
+
     Object deserialize(InputStream is) throws RuntimeIOException
 
     {
 
     {
 
         try {
 
         try {
Line 187: Line 193:
 
             return result;
 
             return result;
 
         } catch (IOException e) {             
 
         } catch (IOException e) {             
             throw new RuntimeSerializationException( e );
+
             throw new RuntimeIOException( e );
 
         }
 
         }
 
     }
 
     }
Line 195: Line 201:
 
</div>
 
</div>
  
It can be replaced with correct method in the next major version release.
+
The faulty method can be replaced with correct one in the next major version release.
 
<div style="background: #f3fff3;">
 
<div style="background: #f3fff3;">
 
<syntaxhighlight lang="java">     
 
<syntaxhighlight lang="java">     
Line 208: Line 214:
 
     {
 
     {
 
         int x = is.read();
 
         int x = is.read();
 +
        ...
 
         return result;
 
         return result;
 
     }
 
     }
Line 214: Line 221:
 
<br/>
 
<br/>
 
</div>
 
</div>
 +
 +
 +
--<br/>
 +
[[User:Toni Kalajainen|Toni Kalajainen]]
 +
 +
[[Category: Miscellaneous Documents]]

Latest revision as of 15:51, 28 January 2011

In this document I have gathered a set of very simple coding conventions. These apply to all org.simantics projects and are recommended for anyone developing with Java. I try to address some of the common mistakes that recur in a multi-developer project. A vast number of bugs can be back-tracked to failure of common understanding, a situation of mis-matching assumptions.

It is natural that our handiwork changes as we grow in experience. Sometimes a developer makes code where the rules or assumptions have changed along the way. For co-developers and future selves it can be a confusing trail. For the reader inconsistent convention leaves room for speculation, and can drive towards reaction-style-coding: guessing and fixing-on-error. Bad quality has a bad manner of propagating forwards, its common in projects with no rules at all. I'll get into more concrete specifics.

By following a common set of rules, hours are saved in avoided debugging. Quality is increased as developer minds can focus on the actual issues.

Java Conventions

Pivotal documents for new java developers:


Argument Assumption

  • All method arguments are non-null unless explicitely stated otherwise in documentation.

The default assumption is that an argument is non-null. This applies to undocumented methods too.

<syntaxhighlight lang="java">

   /**
     * Read the object from a file.
     *
     * @param file 
     */
   void read(File file);
   // and
   void read(File file);

</syntaxhighlight>


A null possibility must be explicitely stated.

<syntaxhighlight lang="java">

   /**
     * Write or remove existing value.
     *
     * @param newValue new value or null</t> to remove the existing value
     */
   void setValue(Object newValue);

</syntaxhighlight>



Return value assumption

  • All return values are non-null unless explicitely stated otherwise in documentation.

The thumb rule is that the return value is non-null. It applies to undocumented methods aswell.

<syntaxhighlight lang="java">

   /**
     * Get the value
     *
     * @return the value
     */
   Object get();
   // and
   Object get();

</syntaxhighlight>


Null option as return value is always explicitely documented.

<syntaxhighlight lang="java">

   /**
     * Get possibly existing value
     *
     * @return the value is exists, otherwise null
     */
   Object get();

</syntaxhighlight>



Trust your assumptions

  • You have a code of conduct - give it a chance.

The callee can trust the caller. Remember VM will do null checkings anyway.

<syntaxhighlight lang="java">

   BigInteger multiply(BigInteger a, BigInteger b) throw IOException {
       return a.multiply(b);
   }

</syntaxhighlight>

And the caller the callee.

<syntaxhighlight lang="java">

   System.out.println( multiply(a, b) );

</syntaxhighlight>


In most cases there is no good reason to do redundant checking, especially at run-time.

<syntaxhighlight lang="java">

   BigInteger multiply(BigInteger a, BigInteger b) throw IOException {
       if ( a == null || b == null ) throw IllegalArgumentException("Non-null argument is expected");
       return a.multiply(b);
   } 

</syntaxhighlight>

Nor caller.

<syntaxhighlight lang="java">

   Object x = multiply( a, b );
   if ( x != null ) System.out.println( x );

</syntaxhighlight>


Use assertions if you must. Checking does improve quality a bit and helps in early detection of problems, but is seldom needed if convention is followed. Assertion is not considered as run-time checking since they can be disabled from the VM.

<syntaxhighlight lang="java" style="background: #dfd;">

   BigInteger multiply(BigInteger a, BigInteger b) {
       assert( a != null && b != null );
       return a.multiply(b);
   }

</syntaxhighlight>


Method migration

This rule applies to code that is published and in wide use.

  • API doesn't change between minor releases.

In case of faulty design, old methods singature are preserved within the major version and marked @Deprecated. They can be removed in the next major release.

<syntaxhighlight lang="java">

   @Deprecated
   Object getValue(Object newValue);

</syntaxhighlight>

  • Documentation is correct, the implementation is faulty.

In situation where there is a mismatch between the documentation and the implementation, the documentation prevails and the fault is in the implementation.


In this example there is problematic method that may return an unexpected null.

<syntaxhighlight lang="java">

   /**
    * Deserialize an object from an input stream.
    *
    * @param is source stream
    * @return the object
    **/
   Object deserialize(InputStream is) {
       try {
           int x = is.read();
           ...
           return result;
       } catch (IOException e) {
          return null;
       }
   }

</syntaxhighlight>

The assumptions that can be derived from the documentation are left unchanged and the implementation is corrected.

<syntaxhighlight lang="java">

   /**
    * Deserialize an object from an input stream.
    *
    * @deprecated use deserialize2, it has better error control
    * @param is source stream
    * @return the object
    * @throws RuntimeIOException in case of IO problems
    **/
   Object deserialize(InputStream is) throws RuntimeIOException
   {
       try {
           int x = is.read();
           ...
           return result;
       } catch (IOException e) {            
           throw new RuntimeIOException( e );
       }
   }

</syntaxhighlight>

The faulty method can be replaced with correct one in the next major version release.

<syntaxhighlight lang="java">

   /**
    * Deserialize an object from an input stream.
    *
    * @param is source stream
    * @return an object
    * @throws IOException in case of problems
    **/
   Object deserialize(InputStream is) throws IOException
   {
       int x = is.read();
       ...
       return result;
   }

</syntaxhighlight>


--
Toni Kalajainen