pdemo.java

这是Java编程艺术一书附带的源代码

// Demonstrate the parser.  
import java.io.*; 
  
class PDemo {  
  public static void main(String args[])  
    throws IOException 
  {  
    String expr; 
 
    BufferedReader br = new 
      BufferedReader(new InputStreamReader(System.in)); 
    Parser p = new Parser();  
  
    System.out.println("Enter an empty expression to stop.");  
  
    for(;;) {  
      System.out.print("Enter expression: ");  
      expr = br.readLine();  
      if(expr.equals("")) break;  
      try { 
        System.out.println("Result: " + p.evaluate(expr));  
        System.out.println(); 
      } catch (ParserException exc) { 
        System.out.println(exc); 
      } 
    }  
  }  
}