Interpreter pattern

最新推荐文章于 2025-01-05 00:04:42 发布

stephenbute

最新推荐文章于 2025-01-05 00:04:42 发布

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分类专栏： Design Pattern 文章标签： string token iterator parsing list tree

本文链接：https://blog.youkuaiyun.com/stephenbute/article/details/1512538

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本文介绍了一种简单的解析器设计与实现方法，该方法能够解析特定的字符串表达式，并通过组合模式、访问者模式和迭代器模式等设计模式来处理和解释解析结果。

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Definition

Provides a definition of a macro language or syntax and parsing into objects in a program.

Where to use & benefits

Need your own parser generator.
Translate a specific expression.
Handle a tree-related information.

Related patterns include

Composite, which is an instance in an interpreter.
Flyweight, which shows how to share symbols with abstract context.
Iterator, which is used to traverse the tree structure.
Visitor, which is used to maintain behavior of each note in tree structure.

Example

Given any string expression and a token, filter out the information you want. The below is a simple parser program. the myParser method can be used to parse any expression. The composite, visit and iterator patterns have been used.
import java.util.*;
class Parser{
    private String expression;
    private String token;
    private List result;
    private String interpreted;

    public Parser(String e, String t) {
       expression = e;
       token = t;
    }

    public void myParser() {
        StringTokenizer holder = new StringTokenizer(expression, token);
        String[] toBeMatched = new String[holder.countTokens()];
        int idx = 0;
        while(holder.hasMoreTokens()) {
            String item = holder.nextToken();
            int start = item.indexOf(",");
            if(start==0) {
               item = item.substring(2);
            }
        toBeMatched[idx] = item;
        idx ++;
        }
        result = Arrays.asList(toBeMatched);
     }
     public List getParseResult() {
        return result;
     }
     public void interpret() {
         StringBuffer buffer = new StringBuffer();
         ListIterator list = result.listIterator();
         while (list.hasNext()){
            String token = (String)list.next();
            if (token.equals("SFO")){
               token = "San Francisco";
            }else if(token.equals("CA")) {
               token = "Canada";
            }
            //...
            buffer.append(" " + token);
         }
         interpreted = buffer.toString();
     }
     public String getInterpretedResult() {
        return interpreted;
     }
     public static void main(String[] args) {
         String source = "dest='SFO',origin='CA',day='MON'";
         String delimiter = "=,'";
         Parser parser = new Parser(source, delimiter);
         parser.myParser();
         parser.interpret();
         String result = parser.getInterpretedResult();
         System.out.println(result);
     }
}