用Java编写 LR(0)分析表的构造

以下是使用Java语言编写LR(0)分析表构造的示例代码：

import java.util.*;

public class LR0Parser {

    private Grammar grammar; // 存储文法的对象

    private Map<String, Integer> nonTerminals; // 非终结符号的编号
    private Map<String, Integer> terminals; // 终结符号的编号

    private List<Set<Item>> canonicalCollection; // LR(0)自动机的状态集合

    private int[][] actionTable; // 移进-规约表
    private int[][] gotoTable; // 转移表

    public LR0Parser(Grammar grammar) {
        this.grammar = grammar;
        this.nonTerminals = new HashMap<>();
        this.terminals = new HashMap<>();
        this.canonicalCollection = new ArrayList<>();
        this.actionTable = null;
        this.gotoTable = null;
    }

    public void buildTables() {
        // 初始化非终结符号和终结符号的编号
        int id = 0;
        for (String symbol : grammar.getSymbols()) {
            if (grammar.isNonTerminal(symbol)) {
                nonTerminals.put(symbol, id++);
            } else {
                terminals.put(symbol, id++);
            }
        }

        // 构造LR(0)自动机
        canonicalCollection.add(closure(new HashSet<>(Collections.singletonList(
                new Item(grammar.getProduction(0), 0)))));
        int i = 0;
        while (i < canonicalCollection.size()) {
            Set<Item> itemSet = canonicalCollection.get(i++);
            for (String symbol : grammar.getSymbols()) {
                Set<Item> nextSet = gotoSet(itemSet, symbol);
                if (!nextSet.isEmpty() && !canonicalCollection.contains(nextSet)) {
                    canonicalCollection.add(nextSet);
                }
            }
        }

        // 构造移进-规约表和转移表
        actionTable = new int[canonicalCollection.size()][terminals.size()];
        gotoTable = new int[canonicalCollection.size()][nonTerminals.size()];
        for (i = 0; i < canonicalCollection.size(); i++) {
            Set<Item> itemSet = canonicalCollection.get(i);
            for (Item item : itemSet) {
                if (item.isReduceItem()) {
                    Production production = item.getProduction();
                    int j = nonTerminals.get(production.getLeft());
                    if (actionTable[i][terminals.size() - 1] != 0) {
                        throw new RuntimeException("LR(0)文法不是SLR文法");
                    }
                    actionTable[i][terminals.size() - 1] = -production.getId() - 1;
                } else {
                    String symbol = item.getSymbol();
                    int j = grammar.isNonTerminal(symbol) ? nonTerminals.get(symbol) : terminals.get(symbol);
                    int k = canonicalCollection.indexOf(gotoSet(itemSet, symbol));
                    if (grammar.isNonTerminal(symbol)) {
                        gotoTable[i][j] = k;
                    } else {
                        actionTable[i][j] = k;
                    }
                }
            }
        }
    }

    public int parse(List<Token> tokens) {
        Stack<Integer> stateStack = new Stack<>(); // 状态栈
        Stack<Integer> symbolStack = new Stack<>(); // 符号栈
        stateStack.push(0);
        symbolStack.push(terminals.get("$"));
        for (Token token : tokens) {
            int state = stateStack.peek();
            int symbol = token.getType();
            int action = actionTable[state][symbol];
            if (action > 0) {
                // 移进操作
                stateStack.push(action);
                symbolStack.push(symbol);
            } else if (action < 0) {
                // 规约操作
                Production production = grammar.getProduction(-action - 1);
                for (int i = 0; i < production.getRight().size(); i++) {
                    stateStack.pop();
                    symbolStack.pop();
                }
                int newState = gotoTable[stateStack.peek()][nonTerminals.get(production.getLeft())];
                stateStack.push(newState);
                symbolStack.push(nonTerminals.get(production.getLeft()));
            } else {
                // 错误处理
                throw new RuntimeException("语法错误");
            }
        }
        return symbolStack.pop();
    }

    // 计算项目集闭包
    private Set<Item> closure(Set<Item> itemSet) {
        Queue<Item> queue = new LinkedList<>(itemSet);
        while (!queue.isEmpty()) {
            Item item = queue.poll();
            if (!item.isReduceItem() && grammar.isNonTerminal(item.getSymbol())) {
                String symbol = item.getNextSymbol();
                for (Production production : grammar.getProductions(symbol)) {
                    Item newItem = new Item(production, 0);
                    if (!itemSet.contains(newItem)) {
                        itemSet.add(newItem);
                        queue.offer(newItem);
                    }
                }
            }
        }
        return itemSet;
    }

    // 计算项目集的转移
    private Set<Item> gotoSet(Set<Item> itemSet, String symbol) {
        Set<Item> result = new HashSet<>();
        for (Item item : itemSet) {
            if (!item.isReduceItem() && item.getSymbol().equals(symbol)) {
                result.add(new Item(item.getProduction(), item.getPosition() + 1));
            }
        }
        return closure(result);
    }
}

注：上述代码中，`Grammar`是一个存储文法的对象，`Token`是一个存储词法分析结果的对象，`Item`是一个表示项目的对象，`Production`是一个表示产生式的对象。在实际使用中，需要根据具体的需求进行相应的修改和扩展。