As part of a software package I'm working on, I need to implement a parser for application specific text files. I've already specified the grammar for these file on paper, but am having a hard time translating it into easily readable/updatable code (right now just it passes each line through a huge number of switch statements).
So, are there any good design patterns for implementing a parser in a Java style OO environment?
Any easy way to break a massive switch into an OO design would be to have
pseudo code
class XTokenType {
public bool isToken(string data);
}
class TokenParse {
public void parseTokens(string data) {
for each step in data {
for each tokenType in tokenTypess {
if (tokenType.isToken(step)) {
parsedTokens[len] = new tokenType(step);
}
...
}
}
...
}
}
Here your breaking each switch statement into a method on that token object to detect whether the next bit of the string is of that token type.
Previously:
class TokenParse {
public void parseTokens(string data) {
for each step in data {
switch (step) {
case x:
...
case y:
...
...
}
}
...
}
}
One suggestion is to create property file where you define rules. Load it during run time and use if else loop (since switch statements also does the same internally). This way if you want to change some parsing rules you have to change .property file not code. :)
You need to learn how to express context free grammars. You should be thinking about the GoF Interpreter and parser/generators like Bison, ANTRL, lex/yacc, etc.
