ll1型文法java实现

LL(1)文法是一种上下文无关文法，它可以被用来描述自然语言，编程语言等等。在LL(1)文法中，每个非终结符都有一组产生式，而每个产生式的右部第一个符号相同。因此，LL(1)文法可以被用来构建递归下降语法分析器。

以下是一个简单的LL(1)文法的Java实现：

1. 定义一个非终结符类：

public class NonTerminal {
private String name;
private List<List<Symbol>> productions;

public NonTerminal(String name) {
this.name = name;
this.productions = new ArrayList<>();
}

public String getName() {
return name;
}

public List<List<Symbol>> getProductions() {
return productions;
}
}

2. 定义一个符号类：

public abstract class Symbol {
public abstract boolean isTerminal();
}

3. 定义一个终结符类：

public class Terminal extends Symbol {
private String name;

public Terminal(String name) {
this.name = name;
}

public String getName() {
return name;
}

@Override
public boolean isTerminal() {
return true;
}
}

4. 定义一个文法类：

public class Grammar {
private List<NonTerminal> nonTerminals;
private List<Terminal> terminals;
private Map<NonTerminal, Set<Terminal>> firstSets;
private Map<NonTerminal, Set<Terminal>> followSets;
private Map<NonTerminal, Map<Terminal, List<Symbol>>> parsingTable;

public Grammar(List<NonTerminal> nonTerminals, List<Terminal> terminals) {
this.nonTerminals = nonTerminals;
this.terminals = terminals;
this.firstSets = new HashMap<>();
this.followSets = new HashMap<>();
this.parsingTable = new HashMap<>();
}

public List<NonTerminal> getNonTerminals() {
return nonTerminals;
}

public List<Terminal> getTerminals() {
return terminals;
}

public Map<NonTerminal, Set<Terminal>> getFirstSets() {
return firstSets;
}

public Map<NonTerminal, Set<Terminal>> getFollowSets() {
return followSets;
}

public Map<NonTerminal, Map<Terminal, List<Symbol>>> getParsingTable() {
return parsingTable;
}

public void calculateFirstSets() {
// TODO: 实现计算First集的算法
}

public void calculateFollowSets() {
// TODO: 实现计算Follow集的算法
}

public void constructParsingTable() {
// TODO: 实现构造分析表的算法
}
}

5. 定义一个递归下降语法分析器类：

public class RecursiveDescentParser {
private Grammar grammar;
private Stack<Symbol> stack;
private TokenStream tokenStream;
private Map<Terminal, Map<Terminal, Integer>> precedenceTable;

public RecursiveDescentParser(Grammar grammar, TokenStream tokenStream, Map<Terminal, Map<Terminal, Integer>> precedenceTable) {
this.grammar = grammar;
this.stack = new Stack<>();
this.tokenStream = tokenStream;
this.precedenceTable = precedenceTable;
}

public void parse() {
stack.push(grammar.getNonTerminals().get(0));
Token currentToken = tokenStream.getCurrentToken();

while (!stack.isEmpty()) {
Symbol top = stack.pop();

if (top.isTerminal()) {
if (top.equals(currentToken.getSymbol())) {
currentToken = tokenStream.getNextToken();
} else {
// 异常处理
}
} else {
Map<Terminal, List<Symbol>> row = grammar.getParsingTable().get(top);

if (row == null) {
// 异常处理
}

List<Symbol> production = row.get(currentToken.getSymbol());

if (production == null) {
// 异常处理
}

for (int i = production.size() - 1; i >= 0; i--) {
stack.push(production.get(i));
}
}
}
}
}

这些代码仅仅是LL(1)文法在Java中的一个简单实现，实际上还有很多细节需要考虑。但是，这应该足够给你一个概述LL(1)文法在Java中的实现方式。