用Java语言给上面的分析表编写LR(0)分析器

以下为基于LR(0)分析表的Java代码实现：

import java.util.HashMap;
import java.util.Map;
import java.util.Stack;

public class LR0Parser {
    private static final int[][] GOTO_TABLE = {
            {1, 3},
            {0, 0},
            {1, 3},
            {0, 0},
            {0, 0},
            {0, 0},
            {0, 0},
            {0, 0},
            {0, 0},
            {0, 0},
            {0, 0}
    };

    private static final int[][] ACTION_TABLE = {
            {2, 0, 4, 0, 0},
            {0, 0, 0, 0, 1},
            {5, 6, 4, 0, 0},
            {5, 6, 0, 0, 0},
            {0, 0, 0, 0, 2},
            {5, 0, 4, 0, 0},
            {5, 6, 4, 0, 0},
            {0, 6, 0, 4, 4},
            {5, 0, 4, 0, 0},
            {5, 6, 0, 1, 1},
            {0, 6, 0, 3, 3}
    };

    public static void main(String[] args) {
        String input = "a+a*a";
        Stack<Integer> stateStack = new Stack<>();
        Stack<Character> symbolStack = new Stack<>();
        stateStack.push(0);
        int index = 0;

        while (index < input.length()) {
            int currentState = stateStack.peek();
            char currentSymbol = input.charAt(index);
            int action = getAction(currentState, currentSymbol);
            if (action > 0) {
                stateStack.push(action);
                symbolStack.push(currentSymbol);
                index++;
            } else if (action < 0) {
                int reduceLength = -action;
                String production = reduce(reduceLength);
                if (production.equals("E->T")) {
                    symbolStack.pop();
                    stateStack.pop();
                    stateStack.push(GOTO_TABLE[stateStack.peek()][0]);
                    symbolStack.push('E');
                } else if (production.equals("E->E+T")) {
                    symbolStack.pop();
                    symbolStack.pop();
                    stateStack.pop();
                    stateStack.push(GOTO_TABLE[stateStack.peek()][0]);
                    symbolStack.push('E');
                } else if (production.equals("T->a")) {
                    stateStack.pop();
                    stateStack.push(GOTO_TABLE[stateStack.peek()][1]);
                    symbolStack.push('T');
                } else if (production.equals("T->(E)")) {
                    symbolStack.pop();
                    stateStack.pop();
                    symbolStack.pop();
                    stateStack.pop();
                    stateStack.push(GOTO_TABLE[stateStack.peek()][1]);
                    symbolStack.push('T');
                }
            } else {
                System.out.println("Invalid input");
                break;
            }
        }

        int currentState = stateStack.peek();
        int action = ACTION_TABLE[currentState][4];
        if (action == 1) {
            System.out.println("Accepted");
        } else {
            System.out.println("Rejected");
        }
    }

    private static int getAction(int state, char symbol) {
        int index = -1;
        switch (symbol) {
            case 'a':
                index = 0;
                break;
            case '+':
                index = 1;
                break;
            case '(':
                index = 2;
                break;
            case ')':
                index = 3;
                break;
            case '$':
                index = 4;
                break;
            default:
                break;
        }
        return ACTION_TABLE[state][index];
    }

    private static String reduce(int length) {
        Map<Integer, String> productionMap = new HashMap<>();
        productionMap.put(1, "E->E+T");
        productionMap.put(2, "E->T");
        productionMap.put(3, "T->T*a");
        productionMap.put(4, "T->a");
        productionMap.put(5, "T->(E)");
        return productionMap.get(length);
    }
}

注：上述代码中的 ACTION_TABLE 和 GOTO_TABLE 分别对应于前面所给的 LR(0)分析表中的 ACTION_TABLE 和 GOTO_TABLE。输入的字符串为"a+a*a"。