Warum einfach, wenns auch kompliziert geht?


(Why make it simple, when you can also make it complicated?) Consider the task of associating code with specific data values. Using a multi-way conditional can be error-prone, because the data values become separated by the code. It can also be inefficient in the cases where we have to use cascading else if statements, instead of a switch, which the compiler can optimize into a hash table. In C I would use an array containing values and function pointers. My understanding is that the Java approach involves using the Strategy pattern: a separate class for each case, and an interface "to rule them all".

Here is the C code from the NetBSD ifconfig implementation.
void    setifflags (char *, int);
void    notrailers (char *, int);
/* [...] */
void    setifdstaddr (char *, int);

struct  cmd {
    char    *c_name;
    int     c_parameter;
    void    (*c_func) (char *, int);
} cmds[] = {
    { "up",         IFF_UP,     setifflags } ,
    { "down",       -IFF_UP,    setifflags },
    { "trailers",   -1,         notrailers },
    { "-trailers",  1,          notrailers },
    /* [...] */
    { 0,            0,          setifdstaddr },
An here is the annotated Java implementation of the corresponding contruct in Apache's Tomcat Jasper code.
Replacing multi-way branching using the Strategy pattern

As they say, the code speaks for itself. I believe the implementation is way too complicated for what it is trying to achieve. On the other hand, the programmer was just trying to overcome a limitation of the Java programming language: in Java methods are not first (or even second) class citizens.
(My thanks to my colleagues Panagiotis Louridas and Spyros Oikonomopoulos for a fruitful discussion on this topic.)

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Last modified: Friday, May 13, 2005 9:54 am

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