针对Java的词法分析输出token序列

好的，针对Java的词法分析输出token序列，可以使用词法分析器（lexer）来实现。以下是一个简单的Java词法分析器示例，它可以将输入的Java代码分解成一个个的token：

import java.util.*;

public class JavaLexer {
    private String input;
    private List<String> tokens;
    private int pos;

    public JavaLexer(String input) {
        this.input = input;
        this.tokens = new ArrayList<>();
        this.pos = 0;
    }

    public List<String> getTokens() {
        return tokens;
    }

    public void tokenize() {
        while (pos < input.length()) {
            char currentChar = input.charAt(pos);
            if (Character.isLetter(currentChar)) {
                String identifier = readIdentifier();
                tokens.add(identifier);
            } else if (Character.isDigit(currentChar)) {
                String number = readNumber();
                tokens.add(number);
            } else if (currentChar == '\"') {
                String stringLiteral = readStringLiteral();
                tokens.add(stringLiteral);
            } else if (currentChar == '\'') {
                String charLiteral = readCharLiteral();
                tokens.add(charLiteral);
            } else if (isOperator(currentChar)) {
                String operator = readOperator();
                tokens.add(operator);
            } else if (isDelimiter(currentChar)) {
                String delimiter = readDelimiter();
                tokens.add(delimiter);
            } else {
                // skip unknown character
                pos++;
            }
        }
    }

    private String readIdentifier() {
        StringBuilder sb = new StringBuilder();
        while (pos < input.length() && (Character.isLetterOrDigit(input.charAt(pos)) || input.charAt(pos) == '_')) {
            sb.append(input.charAt(pos));
            pos++;
        }
        return sb.toString();
    }

    private String readNumber() {
        StringBuilder sb = new StringBuilder();
        while (pos < input.length() && Character.isDigit(input.charAt(pos))) {
            sb.append(input.charAt(pos));
            pos++;
        }
        return sb.toString();
    }

    private String readStringLiteral() {
        StringBuilder sb = new StringBuilder();
        pos++; // skip opening quote
        while (pos < input.length() && input.charAt(pos) != '\"') {
            sb.append(input.charAt(pos));
            pos++;
        }
        pos++; // skip closing quote
        return "\"" + sb.toString() + "\"";
    }

    private String readCharLiteral() {
        StringBuilder sb = new StringBuilder();
        pos++; // skip opening quote
        while (pos < input.length() && input.charAt(pos) != '\'') {
            sb.append(input.charAt(pos));
            pos++;
        }
        pos++; // skip closing quote
        return "\'" + sb.toString() + "\'";
    }

    private String readOperator() {
        StringBuilder sb = new StringBuilder();
        while (pos < input.length() && isOperator(input.charAt(pos))) {
            sb.append(input.charAt(pos));
            pos++;
        }
        return sb.toString();
    }

    private String readDelimiter() {
        String delimiter = String.valueOf(input.charAt(pos));
        pos++;
        return delimiter;
    }

    private boolean isOperator(char c) {
        return "+-*/%=<>!&|".indexOf(c) != -1;
    }

    private boolean isDelimiter(char c) {
        return "(){}[],.;:".indexOf(c) != -1;
    }
}

使用方法：

String input = "public class HelloWorld {\n" +
               "    public static void main(String[] args) {\n" +
               "        System.out.println(\"Hello, world!\");\n" +
               "    }\n" +
               "}";
JavaLexer lexer = new JavaLexer(input);
lexer.tokenize();
List<String> tokens = lexer.getTokens();
System.out.println(tokens);

输出结果：

[public, class, HelloWorld, {, public, static, void, main, (, String, [, ], args, ), {, System, ., out, ., println, (, "Hello, world!", ), ;, }, }]

可以看到，输出的结果是一个token序列，其中包含了Java代码中的所有关键字、标识符、数字、字符串、字符、运算符和分隔符等。