CheatSheat

eliminate_lr.java

package practice;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Scanner;

public class eliminate_lr {

    private static final ArrayList<LinkedList<String>> lists = new ArrayList<>();

    public static void main(String[] args) {
        File cfg = new File("src/samplecfg2.txt");
        try {
            Scanner scanner = new Scanner(cfg);
            while (scanner.hasNextLine()) {
                String line = scanner.nextLine();
                String[] x = line.split("->");

                LinkedList<String> list = new LinkedList<>();
                list.add(x[0].trim());

                String[] rules = x[1].split("\\|");
                for (String rule : rules) {
                    rule = rule.trim();
                    if (!rule.equals(""))
                        list.add(rule);
                }

                lists.add(list);
            }

            // Print Linked list
            System.out.println(lists);

            reduceCFG();

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }

    private static LinkedList<String> getListFromNT(String nt) {
        for (LinkedList<String> rules : lists) {
            if (rules.get(0).equals(nt))
                return rules;
        }
        return null;
    }

    private static void eliminateLR(String nt, int i) {
        LinkedList<String> list = getListFromNT(nt);
        if (list == null)
            return;

        String alpha = list.get(i).replaceFirst(nt, "");
        ArrayList<String> betas = new ArrayList<>();
        for (String rule : list) if (!rule.startsWith(nt)) betas.add(rule);

        // New Rules
        StringBuilder nRule = new StringBuilder(nt).append(" -> ");
        for (int j = 0, betasSize = betas.size(); j < betasSize; j++) {
            String beta = betas.get(j);
            nRule.append(beta).append(nt).append("'");
            if(j != betasSize - 1)
                nRule.append(" | ");
        }

        System.out.println(nRule);
        System.out.println(nt + "' -> " + alpha + nt + "' | ɛ ");
    }

    private static void reduceCFG() {
        for (LinkedList<String> rules : lists) {
            String nt = rules.get(0);
            for (int i = 1; i < rules.size(); i++) {
                if (rules.get(i).startsWith(nt)) {
                    System.out.println("Left Recursion Detected!\nPossible Elimination");
                    eliminateLR(nt, i);
                }
            }
        }
    }
}

load_cfg.java

package practice;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Scanner;

public class load_cfg {

    private static final ArrayList<LinkedList<String>> lists = new ArrayList<>();

    public static void main(String[] args) {
        File cfg = new File("src/samplecfg.txt");
        try {
            Scanner scanner = new Scanner(cfg);
            while (scanner.hasNextLine()){
                String line = scanner.nextLine();
                String[] x = line.split("->");

                LinkedList<String> list = new LinkedList<>();
                list.add(x[0]);

                String[] rules = x[1].split("\\|");
                for(String rule: rules){
                    rule = rule.trim();
                    if(!rule.equals(""))
                        list.add(rule);
                }

                lists.add(list);
            }

            // Print Linked list
            System.out.println(lists);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }
}

recognize_identifiers.java

package practice;

public class recognize_identifiers {

    public static boolean isIdentifier(String tok){
        return tok.matches("[_a-zA-Z][_a-zA-Z0-9]*");
    }

    public static void main(String[] args) {
        System.out.println(isIdentifier("123"));
    }
}

recognize_keywords.java

package practice;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class recognize_keywords {

    private static final String[] KEYWORDS = {
            "int",
            "String",
            "char",
            "static",
            "if",
            "boolean",
            "private",
            "public",
            "protected",
            "else",
            "long",
            "class",
            "void",
            "true",
            "false",
            "return",
            "final",
            "try",
            "catch"
    };

    private static boolean isKeyword(String tok){
        for (String keyword : KEYWORDS) if (keyword.equals(tok)) return true;
        return false;
    }

    public static void main(String[] args) {
        File codeFile = new File("src/practice/recognize_keywords.java");
        try {
            Scanner reader = new Scanner(codeFile);
            while (reader.hasNextLine()){
                String line = reader.nextLine();
                String[] tokens = line.split(" ");
                for (String token: tokens) if (isKeyword(token)) System.out.println("Keyword: " + token);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }
}