PL/0编译器(java version) – Scanner.java

   1:  package compiler;

   2:   

   3:  import java.io.BufferedReader;

   4:  import java.io.FileNotFoundException;

   5:  import java.io.FileReader;

   6:  import java.util.Arrays;

   7:   

   8:  public class Scanner {

   9:   

  10:      public int lineCnt=0;

  11:      private char curCh = ' ';

  12:      private String line;

  13:      public int lineLength = 0;

  14:      public int chCount = 0;

  15:      private int[] ssym;

  16:      private BufferedReader in;

  17:   

  18:      public Scanner(String filePath) {

  19:          try {

  20:              in = new BufferedReader(new FileReader(filePath));

  21:          } catch (FileNotFoundException ex) {

  22:              ex.printStackTrace();

  23:              System.out.println("***File not exist!***");

  24:          }

  25:          //设置单字符

  26:          ssym = new int[256];

  27:          Arrays.fill(ssym, Symbol.nul);

  28:          ssym['+'] = Symbol.plus;

  29:          ssym['-'] = Symbol.minus;

  30:          ssym['*'] = Symbol.mul;

  31:          ssym['/'] = Symbol.div;

  32:          ssym['('] = Symbol.lparen;

  33:          ssym[')'] = Symbol.rparen;

  34:          ssym['='] = Symbol.eql;

  35:          ssym[','] = Symbol.comma;

  36:          ssym['.'] = Symbol.peroid;

  37:          ssym[';'] = Symbol.semicolon;

  38:   

  39:      }

  40:   

  41:      //读取一个字符，为减少磁盘I/O次数，每次读取一行

  42:      void getch() {

  43:          if (chCount == lineLength) {

  44:              try {//如果读到行末尾，就重新读入一行

  45:                  String tmp="";

  46:                  while (tmp.equals("")) {

  47:                      tmp=in.readLine().trim()+' ';               //除去空行

  48:                  }

  49:                  line=tmp;

  50:                  lineCnt++;

  51:              } catch (Exception e) {

  52:                  // throw new Error("***program imcomplete!***");

  53:                  e.printStackTrace();

  54:                  System.out.println("***reading character meet with error!***");

  55:              }

  56:              lineLength = line.length();

  57:              chCount = 0;

  58:              System.out.println(line);

  59:          }

  60:          curCh = line.charAt(chCount++);

  61:      }

  62:   

  63:      //词法分析，获取一个词法分析符号，是词法分析器的重点

  64:      public Symbol getsym() {

  65:          Symbol sym;

  66:          while (curCh == ' ') {

  67:              getch();

  68:          }

  69:          if ((curCh >= 'a' && curCh <= 'z')||(curCh >= 'A' && curCh <= 'Z')) {

  70:              sym = matchKeywordOrIdentifier();                                     //关键字或者一般标识符

  71:          } else if (curCh >= '0' && curCh <= '9') {

  72:              sym = matchNumber();                                                       //数字

  73:          } else {

  74:              sym = matchOperator();                                                     //操作符

  75:          }

  76:          return sym;

  77:      }

  78:   

  79:      private Symbol matchKeywordOrIdentifier() {

  80:          StringBuffer sb = new StringBuffer();

  81:          do{

  82:              sb.append(curCh);

  83:              getch();

  84:          }while((curCh >= 'a' && curCh <= 'z')||(curCh>='A'&&curCh<='Z') || (curCh >= '0' && curCh <= '9'));

  85:   

  86:          String token = sb.toString();

  87:          int index = Arrays.binarySearch(Symbol.word, token);                           //搜索是不是保留字

  88:          Symbol sym = null;

  89:          if (index < 0) {

  90:              sym = new Symbol(Symbol.ident);                                            //一般标识符

  91:              sym.id = token;

  92:          } else {

  93:              sym = new Symbol(Symbol.wsym[index]);                                    //保留字对应的符号值0-31

  94:          }

  95:          return sym;

  96:      }

  97:   

  98:      private Symbol matchNumber() {

  99:          //统计数字位数

 100:          Symbol sym = new Symbol(Symbol.number);

 101:          do {                      

 102:              sym.num = 10 * sym.num + curCh - '0';                                    // 获取数字的值

 103:              getch();

 104:          } while (curCh >= '0' && curCh <= '9');                                    //!!!

 105:   

 106:          return sym;

 107:      }

 108:   

 109:      private Symbol matchOperator() {

 110:          Symbol sym = null;

 111:          switch (curCh) {

 112:              case ':':                                                                       // 赋值符号

 113:                  getch();

 114:                  if (curCh == '=') {

 115:                      sym = new Symbol(Symbol.becomes);

 116:                      getch();

 117:                  } else {

 118:                      sym = new Symbol(Symbol.nul);                               //不能识别的符号

 119:                  }

 120:                  break;

 121:              case '<':                                                                    //小于或者小于等于

 122:                  getch();

 123:                  if (curCh == '=') {

 124:                      sym = new Symbol(Symbol.leq);                             //是<=

 125:                      getch();

 126:                  } else if (curCh == '>') {

 127:                      sym = new Symbol(Symbol.neq);                           //是<>

 128:                      getch();

 129:                  } else {

 130:                      sym = new Symbol(Symbol.lss);                             //是<

 131:                  }

 132:                  break;

 133:              case '>':                                                      //大于或者大于等于

 134:                  getch();

 135:                  if (curCh == '=') {

 136:                      sym = new Symbol(Symbol.geq);                           //大于等于

 137:                      getch();

 138:                  } else {

 139:                      sym = new Symbol(Symbol.gtr);                            //大于

 140:                  }

 141:                  break;

 142:              default:

 143:                  sym = new Symbol(ssym[curCh]);

 144:                  if (sym.symtype != Symbol.peroid) {

 145:                      getch();

 146:                  }

 147:          }

 148:          return sym;

 149:      }

 150:  }

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