fix: up

dragonbook/src/Parser.java

@@ -0,0 +1,41 @@
+import java.io.IOException;
+
+/**
+ * Parser
+ */
+public class Parser {
+    static int lookahead;
+
+    public Parser() throws IOException {
+        lookahead = System.in.read();
+    }
+
+    void expr() throws IOException {
+        term();
+        while (true) {
+            if (lookahead == '+') {
+                match('+');
+                term();
+                System.out.print('+');
+            } else if(lookahead == '-') {
+                match('-');
+                term();
+                System.out.print('-');
+            } else {
+                return;
+            }
+        }
+    }
+
+    void term() throws IOException {
+        if (Character.isDigit(lookahead)) {
+            System.out.print((char) lookahead);
+            match(lookahead);
+        } else throw new Error("syntax error");
+    }
+
+    void match(int t) throws IOException {
+        if (lookahead == t) lookahead = System.in.read();
+        else throw new Error("syntax error");
+    }
+}

dragonbook/src/Postfix.java

@@ -0,0 +1,12 @@
+import java.io.IOException;
+
+/*
+ * 将中缀表达式翻译为后缀表达
+ */
+public class Postfix {
+    public static void main(String[] args) throws IOException {
+        Parser parser = new Parser();
+        parser.expr();
+        System.out.println('\n');
+    }
+}

dragonbook/src/lexer/Lexer.java

@@ -0,0 +1,93 @@
+package lexer;
+
+import java.io.IOException;
+import java.util.Hashtable;
+
+/**
+ * 词法分析器
+ */
+public class Lexer {
+    public int line = 1;
+    private char peek = ' ';
+    private Hashtable words = new Hashtable<>();
+    void reserve(Word t) {
+        words.put(t.lexeme, t);
+    }
+    public Lexer() {
+        reserve(new Word(Tag.TRUE, "true"));
+        reserve(new Word(Tag.FALSE, "false"));
+    }
+
+    public Token scan() throws IOException {
+        for(;;peek = (char)System.in.read()) {
+            if (peek == ' ' || peek == '\t') {
+                continue;
+            }
+            else if (peek == '\n') {
+                line++;
+            }
+            else {
+                break;
+            }
+        }
+        // 处理注释
+        if (peek == '/') {
+            peek = (char)System.in.read();
+            if (peek == '/') {
+                do {
+                    peek = (char)System.in.read();
+                } while (peek != '\n');
+            }
+            else if (peek == '*') {
+                // 处理多行注释
+                char prevPeek = ' ';
+                do {
+                    prevPeek = peek;
+                    peek = (char)System.in.read();
+                } while (prevPeek != '*' || peek != '/');
+            }
+            else {
+                throw new IOException("illegal comment");
+            }
+        }
+        // 处理关系运算符
+        if("<>=!".indexOf(peek) > -1) {
+            StringBuffer b = new StringBuffer();
+            b.append(peek);
+            peek = (char)System.in.read();
+            if (peek == '=') {
+                b.append(peek);
+            }
+            return new Rel(b.toString());
+        }
+        // 读取数位序列
+        if (Character.isDigit(peek)) {
+            int v = 0;
+            do {
+                v = 10 * v + Character.digit(peek, 10);
+                peek = (char)System.in.read();
+            } while (Character.isDigit(peek));
+            return new Num(v);
+        }
+        // 分析保留字和标识符
+        if(Character.isLetter(peek)) {
+            StringBuffer b = new StringBuffer();
+            do {
+                b.append(peek);
+                peek = (char)System.in.read();
+            } while (Character.isLetterOrDigit(peek));
+            String s = b.toString();
+            Word w = (Word)words.get(s);
+            if (w != null) {
+                return w;
+            }
+            w = new Word(Tag.ID, s);
+            words.put(s,w);
+            return w;
+        }
+        // 将当前字符作为一个词法单元返回
+        Token t = new Token(peek);
+        peek = ' ';
+        return t;
+    }
+}

dragonbook/src/lexer/Num.java

@@ -0,0 +1,12 @@
+package lexer;
+/**
+ * 数字，常量
+ */
+public class Num extends Token {
+    public final int value;
+    public Num(int v) {
+        super(Tag.NUM);
+        value = v;
+    }
+
+}

dragonbook/src/lexer/Rel.java

@@ -0,0 +1,13 @@
+package lexer;
+
+/**
+ * 关系运算符
+ */
+public class Rel extends Token {
+    public final String lexeme;
+    public Rel(String s) {
+        super(Tag.REL);
+        lexeme = s;
+    }
+
+}

dragonbook/src/lexer/Tag.java

@@ -0,0 +1,9 @@
+package lexer;
+
+public class Tag {
+    public final static int NUM = 256;
+    public final static int ID = 257;
+    public final static int TRUE = 258;
+    public final static int FALSE = 259;
+    public final static int REL = 260;
+}

dragonbook/src/lexer/Word.java

@@ -0,0 +1,12 @@
+package lexer;
+/**
+ * 保留字、标识符
+ * 比如用于保留字 true 的对象可以初始化: <code>new Word("true", Token.TRUE)</code>
+ */
+public class Word extends Token {
+    public final String lexeme;
+    public Word(int t,String s) {
+        super(t);
+        this.lexeme = s;
+    }
+}