디자인패턴 해석자 (Interpreter)

TerminalExpression 과 NoterminalExpression

그 이상 전개되지 않는 표현을 ‘TerminalExpression’ 이라고 부릅니다. 버스나 열차의 종착역을 터이널이라고 하는 것과 비슷합니다. 문법규칙의 종착점입니다. 한편 이와 반대를 ‘NoterminalExpression’ 이라 합니다.

import java.util.*;

public class Context {

    private StringTokenizer tokenizer;

    private String currentToken;

    public Context(String text) {

        tokenizer = new StringTokenizer(text);

        nextToken();

    }

    public String nextToken() {

        if (tokenizer.hasMoreTokens()) {

            currentToken = tokenizer.nextToken();

        } else {

            currentToken = null;

        }

        return currentToken;

    }

    public String currentToken() {

        return currentToken;

    }

    public void skipToken(String token) throws ParseException {

        if (!token.equals(currentToken)) {

            throw new ParseException("Warning: " + token + " is expected, but " + currentToken + " is found.");

        }

        nextToken();

    }

    public int currentNumber() throws ParseException {

        int number = 0;

        try {

            number = Integer.parseInt(currentToken);

        } catch (NumberFormatException e) {

            throw new ParseException("Warning: " + e);

        }

        return number;

    }

}

public abstract class Node {

    public abstract void parse(Context context) throws ParseException;

}

public class ParseException extends Exception {

    public ParseException(String msg) {

        super(msg);

    }

}

import java.util.Vector;

public class CommandListNode extends Node {

    private Vector list = new Vector();

    public void parse(Context context) throws ParseException {

        while (true) {

            if (context.currentToken() == null) {

                throw new ParseException("Missing 'end'");

            } else if (context.currentToken().equals("end")) {

                context.skipToken("end");

                break;

            } else {

                Node commandNode = new CommandNode();

                commandNode.parse(context);

                list.add(commandNode);

            }

        }

    }

    public String toString() {

        return "" + list;

    }

}

public class CommandNode extends Node {

    private Node node;

    public void parse(Context context) throws ParseException {

        if (context.currentToken().equals("repeat")) {

            node = new RepeatCommandNode();

            node.parse(context);

        } else {

            node = new PrimitiveCommandNode();

            node.parse(context);

        }

    }

    public String toString() {

        return node.toString();

    }

}

public class PrimitiveCommandNode extends Node {

    private String name;

    public void parse(Context context) throws ParseException {

        name = context.currentToken();

        context.skipToken(name);

        if (!name.equals("go") && !name.equals("right") && !name.equals("left")) {

            throw new ParseException(name + " is undefined");

        }

    }

    public String toString() {

        return name;

    }

}

public class ProgramNode extends Node {

    private Node commandListNode;

    public void parse(Context context) throws ParseException {

        context.skipToken("program");

        commandListNode = new CommandListNode();

        commandListNode.parse(context);

    }

    public String toString() {

        return "[program " + commandListNode + "]";

    }

}

public class RepeatCommandNode extends Node {

    private int number;

    private Node commandListNode;

    public void parse(Context context) throws ParseException {

        context.skipToken("repeat");

        number = context.currentNumber();

        context.nextToken();

        commandListNode = new CommandListNode();

        commandListNode.parse(context);

    }

    public String toString() {

        return "[repeat " + number + " " + commandListNode + "]";

    }

}

import java.util.*;

import java.io.*;

public class mainClass {

    public static void main(String[] args) {

        try {

            BufferedReader reader = new BufferedReader(new FileReader("program.txt"));

            String text;

            while ((text = reader.readLine()) != null) {

                System.out.println("text = "" + text + """);

                Node node = new ProgramNode();

                node.parse(new Context(text));

                System.out.println("node = " + node);

            }

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

}

a program.txt 파일

program end

program go end

program go right go right go right go right end

program repeat 4 go right end end

program repeat 4 repeat 3 go right go left end right end end