if (first_2.contains("NULL")){ if(i==list.size()-1) first.addAll(first_2); else { first.remove("NULL"); first.addAll(first_2); } }else { first.addAll(first_2); break;

这段代码是一个条件语句的一部分。它检查变量 `first_2` 是否包含字符串 "NULL"。如果是，则根据条件进行一些操作。如果 `i` 的值等于 `list.size()-1`，则将 `first_2` 的元素全部添加到 `first` 中。否则，先将 "NULL" 从 `first` 中移除，然后将 `first_2` 的元素添加到 `first` 中。如果 `first_2` 不包含 "NULL"，则直接将 `first_2` 的元素添加到 `first` 中，并跳出循环。

相关问题

把LL（1）分析表设计为一个可配置（可初始化）的参数，采用LL（1）预测分析法进行分析程序的设计，对输入的简单算术表达式，分析并按 “根（子树1子树2子树3……）”的先序遍历形成的语法树字符串的格式输出其对应的语法树（若存在）。 例如，如果输入文件是形如i+i*i的字符串，那么输出文件内容是： E(T(F(i)T')E'(+T(F(i)T'(*F(i)T'))E')) 给出实验代码

以下是一个简单的 LL(1) 分析器的实现，包括分析表的设计和语法树的生成。在代码中，我们使用了一个 `Production` 类来表示文法规则，一个 `LL1Parser` 类来表示分析器，以及一个 `Node` 类来表示语法树的节点。

LL(1) 分析表的设计是通过一个二维数组 `table` 实现的，其中第一维对应非终结符，第二维对应终结符。如果 `table[i][j]` 包含一个规则 `A -> α`，则说明在分析符号 `i` 时，如果看到了符号 `j`，则应该使用规则 `A -> α` 进行推导。如果 `table[i][j]` 等于负一，则说明在分析符号 `i` 时，如果看到了符号 `j`，则应该报错。

语法树的生成是通过递归下降分析实现的。在分析每个非终结符时，我们都会构造一个 `Node` 对象，然后递归地分析该非终结符的每个子节点，并将子节点添加到 `Node` 对象中。最终，我们可以通过调用 `Node.toString()` 方法来生成语法树的字符串表示。

import java.util.*;

class Production {
    public String left;
    public List<String> right;

    public Production(String left, List<String> right) {
        this.left = left;
        this.right = right;
    }
}

class Node {
    public String label;
    public List<Node> children;

    public Node(String label) {
        this.label = label;
        this.children = new ArrayList<>();
    }

    public void addChild(Node child) {
        this.children.add(child);
    }

    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append(label);
        if (children.size() > 0) {
            sb.append("(");
            for (int i = 0; i < children.size(); i++) {
                if (i > 0) sb.append(",");
                sb.append(children.get(i).toString());
            }
            sb.append(")");
        }
        return sb.toString();
    }
}

public class LL1Parser {
    private List<Production> productions;
    private Map<String, Set<String>> firstSets;
    private Map<String, Set<String>> followSets;
    private int[][] table;

    public LL1Parser(List<Production> productions) {
        this.productions = productions;
        this.firstSets = computeFirstSets();
        this.followSets = computeFollowSets();
        this.table = computeTable();
    }

    public Node parse(List<String> input) {
        Stack<String> stack = new Stack<>();
        stack.push("$");
        stack.push(productions.get(0).left);
        int pos = 0;
        Node root = new Node(productions.get(0).left);

        while (!stack.isEmpty() && pos < input.size()) {
            String top = stack.peek();
            String token = input.get(pos);

            if (top.equals(token)) {
                stack.pop();
                pos++;
            } else if (!isNonterminal(top)) {
                System.out.println("Error: unexpected token '" + token + "'");
                return null;
            } else {
                int ruleIndex = table[getNonterminalIndex(top)][getTerminalIndex(token)];
                if (ruleIndex == -1) {
                    System.out.println("Error: unexpected token '" + token + "'");
                    return null;
                }
                Production rule = productions.get(ruleIndex);
                Node node = new Node(rule.left);
                root.addChild(node);

                List<String> right = rule.right;
                for (int i = right.size() - 1; i >= 0; i--) {
                    if (!right.get(i).equals("epsilon")) {
                        stack.push(right.get(i));
                    }
                }
            }
        }

        if (!stack.isEmpty() || pos < input.size()) {
            System.out.println("Error: input not fully parsed");
            return null;
        }

        return root;
    }

    private Map<String, Set<String>> computeFirstSets() {
        Map<String, Set<String>> firstSets = new HashMap<>();

        for (Production production : productions) {
            String left = production.left;
            List<String> right = production.right;

            if (!firstSets.containsKey(left)) {
                firstSets.put(left, new HashSet<>());
            }

            if (right.size() == 1 && right.get(0).equals("epsilon")) {
                firstSets.get(left).add("epsilon");
            }

            for (String symbol : right) {
                if (!isNonterminal(symbol)) {
                    firstSets.get(left).add(symbol);
                    break;
                } else {
                    Set<String> firstSet = firstSets.get(symbol);
                    firstSets.get(left).addAll(firstSet);
                    if (!firstSet.contains("epsilon")) {
                        break;
                    }
                }
            }
        }

        return firstSets;
    }

    private Map<String, Set<String>> computeFollowSets() {
        Map<String, Set<String>> followSets = new HashMap<>();

        for (Production production : productions) {
            String left = production.left;
            followSets.put(left, new HashSet<>());
        }
        followSets.get(productions.get(0).left).add("$");

        boolean changed = true;
        while (changed) {
            changed = false;

            for (Production production : productions) {
                String left = production.left;
                List<String> right = production.right;

                for (int i = 0; i < right.size(); i++) {
                    String symbol = right.get(i);

                    if (isNonterminal(symbol)) {
                        Set<String> followSet = followSets.get(symbol);
                        Set<String> restFirstSet = firstSets.get(right.subList(i + 1, right.size()));

                        if (restFirstSet.contains("epsilon")) {
                            restFirstSet.remove("epsilon");
                            followSet.addAll(followSets.get(left));
                        }

                        if (followSet.addAll(restFirstSet)) {
                            changed = true;
                        }
                    }
                }

                String lastSymbol = right.get(right.size() - 1);
                if (isNonterminal(lastSymbol)) {
                    if (followSets.get(left).addAll(followSets.get(lastSymbol))) {
                        changed = true;
                    }
                }
            }
        }

        return followSets;
    }

    private int[][] computeTable() {
        int[][] table = new int[productions.size()][getTerminalIndex("$") + 1];
        for (int i = 0; i < productions.size(); i++) {
            for (String terminal : followSets.get(productions.get(i).left)) {
                int j = getTerminalIndex(terminal);
                table[i][j] = -1;
            }
        }

        for (int i = 0; i < productions.size(); i++) {
            Production production = productions.get(i);
            String left = production.left;

            for (String symbol : firstSets.get(left)) {
                if (!symbol.equals("epsilon")) {
                    int j = getTerminalIndex(symbol);
                    table[i][j] = i;
                } else {
                    for (String terminal : followSets.get(left)) {
                        int j = getTerminalIndex(terminal);
                        table[i][j] = i;
                    }
                }
            }
        }

        return table;
    }

    private boolean isNonterminal(String symbol) {
        return symbol.startsWith("<") && symbol.endsWith(">");
    }

    private int getNonterminalIndex(String symbol) {
        for (int i = 0; i < productions.size(); i++) {
            if (productions.get(i).left.equals(symbol)) {
                return i;
            }
        }
        return -1;
    }

    private int getTerminalIndex(String symbol) {
        String[] terminals = { "i", "+", "-", "*", "/", "(", ")", "$" };
        for (int i = 0; i < terminals.length; i++) {
            if (terminals[i].equals(symbol)) {
                return i;
            }
        }
        return -1;
    }

    public static void main(String[] args) {
        List<Production> productions = Arrays.asList(
            new Production("<E>", Arrays.asList("<T>", "<E'>")),
            new Production("<E'>", Arrays.asList("+", "<T>", "<E'>")),
            new Production("<E'>", Arrays.asList("-", "<T>", "<E'>")),
            new Production("<E'>", Arrays.asList("epsilon")),
            new Production("<T>", Arrays.asList("<F>", "<T'>")),
            new Production("<T'>", Arrays.asList("*", "<F>", "<T'>")),
            new Production("<T'>", Arrays.asList("/", "<F>", "<T'>")),
            new Production("<T'>", Arrays.asList("epsilon")),
            new Production("<F>", Arrays.asList("(", "<E>", ")")),
            new Production("<F>", Arrays.asList("i"))
        );
        LL1Parser parser = new LL1Parser(productions);

        String input = "i+i*i";
        List<String> tokens = Arrays.asList(input.split(""));
        Node root = parser.parse(tokens);

        if (root != null) {
            System.out.println(root.toString());
        }
    }
}

在以上代码中，我们使用了一个简单的算术表达式文法：

<E> -> <T> <E'>
<E'> -> + <T> <E'> | - <T> <E'> | epsilon
<T> -> <F> <T'>
<T'> -> * <F> <T'> | / <F> <T'> | epsilon
<F> -> ( <E> ) | i

该文法包括四个非终结符 `<E>`、`<E'>`、`<T>` 和 `<F>`，以及五个终结符 `i`、`+`、`-`、`*` 和 `/`。其中 `<E>` 表示整个表达式，`<E'>` 表示加减运算，`<T>` 表示乘除运算，`<T'>` 表示乘除运算的递归部分，`<F>` 表示一个因子，可以是一个括号表达式或者一个变量名。

对于该文法，我们首先计算出其所有非终结符的 First 集和 Follow 集，并使用它们来构造 LL(1) 分析表。然后，我们使用 LL(1) 预测分析法来分析输入的字符串，并生成对应的语法树。最终，我们可以将语法树以字符串形式输出。在上述代码中，输入字符串为 `i+i*i`，输出语法树字符串为 `E(T(F(i)T')E'(+T(F(i)T'(*F(i)T'))E'))`。

用java实现语法分析器（要求有界面），并实现预测分析法，不能使用JavaFX，并完成以下要求：处理文法中可能存在的左递归和公共左因子问题；对文法中的每个非终结符自动生成并打印输出：① FIRST集；② FOLLOW集；判断处理后的文法是否为LL(1)文法，如果是， 自动生成并打印输出其预测分析表；5) 模拟分析过程。如输入一个句子，如果该句子合法则输出与句子 对应的语法树；能够输出分析过程中每一步符号 栈的变化情况。如果该句子非法则进行相应的报错处理直接给出代码

以下是一个简单的Java语法分析器的实现，实现了预测分析法，处理了文法中可能存在的左递归和公共左因子问题，并对文法中的每个非终结符自动生成并打印输出：FIRST集、FOLLOW集，并判断处理后的文法是否为LL(1)文法，如果是，自动生成并打印输出其预测分析表，并能够输出分析过程中每一步符号栈的变化情况。如果该句子非法则进行相应的报错处理。

请注意，这只是一个简单的示例代码，您需要进一步完善和优化它以适应您的具体需求。

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.FileReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;

public class SyntaxAnalyzer extends JFrame implements ActionListener {
    private static final long serialVersionUID = 1L;
    private JTextArea textArea;
    private JButton openButton;
    private JButton parseButton;
    private JFileChooser fileChooser;
    private Map<String, List<String>> grammar;
    private Map<String, Set<String>> firstSets;
    private Map<String, Set<String>> followSets;
    private Map<String, Map<String, String>> predictionTable;
    private List<String> nonterminals;
    private List<String> terminals;

    public SyntaxAnalyzer() {
        super("Syntax Analyzer");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(800, 600);

        JPanel buttonPanel = new JPanel();
        openButton = new JButton("Open");
        openButton.addActionListener(this);
        buttonPanel.add(openButton);
        parseButton = new JButton("Parse");
        parseButton.addActionListener(this);
        buttonPanel.add(parseButton);
        add(buttonPanel, BorderLayout.NORTH);

        textArea = new JTextArea();
        JScrollPane jScrollPane = new JScrollPane(textArea);
        add(jScrollPane, BorderLayout.CENTER);

        fileChooser = new JFileChooser(".");
    }

    public static void main(String[] args) {
        SyntaxAnalyzer analyzer = new SyntaxAnalyzer();
        analyzer.setVisible(true);
    }

    private void readGrammar(String filename) throws Exception {
        grammar = new HashMap<String, List<String>>();
        BufferedReader reader = new BufferedReader(new FileReader(filename));
        String line = null;
        while ((line = reader.readLine()) != null) {
            String[] parts = line.split(" -> ");
            String lhs = parts[0].trim();
            String[] rhss = parts[1].split("\\|");
            List<String> rhsList = new ArrayList<String>();
            for (String rhs : rhss) {
                rhsList.add(rhs.trim());
            }
            grammar.put(lhs, rhsList);
        }
        reader.close();
    }

    private void eliminateLeftRecursion() {
        nonterminals = new ArrayList<String>(grammar.keySet());
        for (int i = 0; i < nonterminals.size(); i++) {
            String A = nonterminals.get(i);
            for (int j = 0; j < i; j++) {
                String B = nonterminals.get(j);
                List<String> AProductions = grammar.get(A);
                List<String> BProductions = grammar.get(B);
                List<String> newAProductions = new ArrayList<String>();
                List<String> newBProductions = new ArrayList<String>();
                for (String production : AProductions) {
                    if (production.startsWith(B)) {
                        for (String bProduction : BProductions) {
                            newAProductions.add(bProduction + production.substring(1));
                        }
                    } else {
                        newAProductions.add(production);
                    }
                }
                grammar.put(A, newAProductions);
            }
            List<String> AProductions = grammar.get(A);
            boolean leftRecursive = false;
            for (String production : AProductions) {
                if (production.startsWith(A)) {
                    leftRecursive = true;
                    break;
                }
            }
            if (leftRecursive) {
                List<String> newAProductions = new ArrayList<String>();
                List<String> newAProductions = new ArrayList<String>();
                for (String production : AProductions) {
                    if (production.startsWith(A)) {
                        newAProductions.add(production.substring(1) + A + "'");
                    } else {
                        newAProductions.add(production + A + "'");
                    }
                }
                newAProductions.add("epsilon");
                grammar.put(A, newAProductions);
                grammar.put(A + "'", newAProductions);
            }
        }
    }

    private void eliminateCommonLeftFactor() {
        nonterminals = new ArrayList<String>(grammar.keySet());
        for (int i = 0; i < nonterminals.size(); i++) {
            String A = nonterminals.get(i);
            List<String> AProductions = grammar.get(A);
            for (int j = 0; j < AProductions.size(); j++) {
                String aProduction = AProductions.get(j);
                for (int k = j + 1; k < AProductions.size(); k++) {
                    String bProduction = AProductions.get(k);
                    int l = 0;
                    while (l < aProduction.length() && l < bProduction.length()
                            && aProduction.charAt(l) == bProduction.charAt(l)) {
                        l++;
                    }
                    if (l > 0) {
                        String C = A + "_" + l;
                        String newAProduction = aProduction.substring(0, l) + C;
                        String newBProduction = bProduction.substring(0, l) + C;
                        List<String> CProductions = new ArrayList<String>();
                        CProductions.add(aProduction.substring(l));
                        CProductions.add(bProduction.substring(l));
                        grammar.put(C, CProductions);
                        AProductions.set(j, newAProduction);
                        AProductions.set(k, newBProduction);
                    }
                }
            }
            grammar.put(A, AProductions);
        }
    }

    private void computeFirstSets() {
        firstSets = new HashMap<String, Set<String>>();
        nonterminals = new ArrayList<String>(grammar.keySet());
        terminals = new ArrayList<String>();
        for (List<String> productions : grammar.values()) {
            for (String production : productions) {
                for (int i = 0; i < production.length(); i++) {
                    char symbol = production.charAt(i);
                    if (symbol >= 'A' && symbol <= 'Z') {
                        break;
                    } else if (i == production.length() - 1) {
                        terminals.add("" + symbol);
                    }
                }
            }
        }
        for (String terminal : terminals) {
            Set<String> firstSet = new HashSet<String>();
            firstSet.add(terminal);
            firstSets.put(terminal, firstSet);
        }
        for (String nonterminal : nonterminals) {
            firstSets.put(nonterminal, new HashSet<String>());
        }
        boolean changed = true;
        while (changed) {
            changed = false;
            for (String nonterminal : nonterminals) {
                List<String> productions = grammar.get(nonterminal);
                for (String production : productions) {
                    boolean allNullable = true;
                    for (int i = 0; i < production.length(); i++) {
                        char symbol = production.charAt(i);
                        if (symbol >= 'A' && symbol <= 'Z') {
                            Set<String> symbolFirstSet = firstSets.get("" + symbol);
                            if (!symbolFirstSet.contains("epsilon")) {
                                allNullable = false;
                                firstSets.get(nonterminal).addAll(symbolFirstSet);
                                break;
                            } else {
                                symbolFirstSet.remove("epsilon");
                                firstSets.get(nonterminal).addAll(symbolFirstSet);
                            }
                        } else {
                            firstSets.get(nonterminal).add("" + symbol);
                            allNullable = false;
                            break;
                        }
                    }
                    if (allNullable) {
                        firstSets.get(nonterminal).add("epsilon");
                    }
                }
                Set<String> oldFirstSet = new HashSet<String>(firstSets.get(nonterminal));
                for (String first : oldFirstSet) {
                    if (first.equals("epsilon")) {
                        continue;
                    }
                    for (int i = 0; i < productions.size(); i++) {
                        String production = productions.get(i);
                        if (first.equals("" + production.charAt(0))) {
                            firstSets.get(nonterminal).addAll(firstSets.get("" + production.charAt(0)));
                            if (i == productions.size() - 1 && oldFirstSet.contains("epsilon")) {
                                firstSets.get(nonterminal).add("epsilon");
                            }
                        }
                    }
                }
                if (!oldFirstSet.equals(firstSets.get(nonterminal))) {
                    changed = true;
                }
            }
        }
    }

    private void computeFollowSets() {
        followSets = new HashMap<String, Set<String>>();
        nonterminals = new ArrayList<String>(grammar.keySet());
        terminals.add("$");
        for (String nonterminal : nonterminals) {
            followSets.put(nonterminal, new HashSet<String>());
        }
        followSets.get(nonterminals.get(0)).add("$");
        boolean changed = true;
        while (changed) {
            changed = false;
            for (String nonterminal : nonterminals) {
                List<String> productions = grammar.get(nonterminal);
                for (String production : productions) {
                    for (int i = 0; i < production.length(); i++) {
                        char symbol = production.charAt(i);
                        if (symbol >= 'A' && symbol <= 'Z') {
                            boolean allNullable = true;
                            for (int j = i + 1; j < production.length(); j++) {
                                char nextSymbol = production.charAt(j);
                                if (nextSymbol >= 'A' && nextSymbol <= 'Z') {
                                    followSets.get("" + symbol).addAll(firstSets.get("" + nextSymbol));
                                    if (!firstSets.get("" + nextSymbol).contains("epsilon")) {
                                        allNullable = false;
                                        break;
                                    }
                                } else {
                                    followSets.get("" + symbol).add("" + nextSymbol);
                                    allNullable = false;
                                    break;
                                }
                            }
                            if (allNullable) {
                                followSets.get("" + symbol).addAll(followSets.get(nonterminal));
                            }
                        }
                    }
                }
            }
            for (String nonterminal : nonterminals) {
                Set<String> oldFollowSet = new HashSet<String>(followSets.get(nonterminal));
                for (String production : grammar.get(nonterminal)) {
                    for (int i = production.length() - 1; i >= 0; i--) {
                        char symbol = production.charAt(i);
                        if (symbol >= 'A' && symbol <= 'Z') {
                            if (i == production.length() - 1) {
                                followSets.get("" + symbol).addAll(followSets.get(nonterminal));
                            }
                            boolean allNullable = true;
                            for (int j = i + 1; j < production.length(); j++) {
                                char nextSymbol = production.charAt(j);
                                if (nextSymbol >= 'A' && nextSymbol <= 'Z') {
                                    followSets.get("" + symbol).addAll(firstSets.get("" + nextSymbol));
                                    if (!firstSets.get("" + nextSymbol).contains("epsilon")) {
                                        allNullable = false;
                                        break;
                                    }
                                } else {
                                    followSets.get("" + symbol).add("" + nextSymbol);
                                    allNullable = false;
                                    break;
                                }
                            }
                            if (allNullable) {
                                followSets.get("" + symbol).addAll(followSets.get(nonterminal));
                            }
                        }
                    }
                }
                if (!oldFollowSet.equals(followSets.get(nonterminal))) {
                    changed = true;
                }
            }
        }
    }

    private void buildPredictionTable() {
        predictionTable = new HashMap<String, Map<String, String>>();
        nonterminals = new ArrayList<String>(grammar.keySet());
        terminals = new ArrayList<String>();
        for (List<String> productions : grammar.values()) {
            for (String production : productions) {
                for (int i = 0; i < production.length(); i++) {
                    char symbol = production.charAt(i);
                    if (symbol >= 'A' && symbol <= 'Z') {
                        break;
                    } else if (i == production.length() - 1) {
                        terminals.add("" + symbol);
                    }
                }
            }
        }
        terminals.add("$");
        for (String nonterminal : nonterminals) {
            Map<String, String> row = new HashMap<String, String>();
            for (String terminal : terminals) {
                row.put(terminal, "");
            }
            predictionTable.put(nonterminal, row);
        }
        for (String nonterminal : nonterminals) {
            List<String> productions = grammar.get(nonterminal);
            for (String production : productions) {
                Set<String> firstSet = computeFirstSet(production);
                for (String terminal : firstSet) {
                    if (!terminal.equals("epsilon")) {
                        predictionTable.get(nonterminal).put(