calcface.java

本“计算器”可以完成任意的通常借助手持计算器来完成的标准运算。“计算器”可用于基本的算术运算

///////    CalcFace.java    ///////

import java.io.*;

//用户接口对象，该对象将用户输入报告给Calculator并显示结果
class CalcFace		
{ 
   public CalcFace(String k, int pr)
   {  keys = k;  prec = pr++; 
      nbuf = new StringBuffer(prec);		//	定义字符串缓冲区nbuf
      reset();
   } 

   protected CalcFace() {}
   
   public void setCalc(Calculator ca)
   {  calc = ca; }

   public void showStatus(String e)
   {   prompt = ( e.length() == 0 ) 
                ? "Calc:  "
                : "Calc [" + e + "]:  "; 
   }

   public void showOp(char op) { }

   public void errorInput(String str)
   {   errMode = true;		//	错误模式
       active = str;
   }

   public void showNumber(String s) 
   {   System.out.println(prompt + s);
   }

   public void input()
       throws IOException
   {   int i;
       while ( (i= inchar()) != -1 )
       {   enter((char) i);   } 
   }

   protected void enter(char c)
   {   if ( errMode )
       {   if ( active.indexOf(c) == -1) return;
                else errMode = false;
       }
       if ( keys.indexOf(c) != -1 )   // if c an operator
       {  showOp(c);
          if ( num )				//	if num not null
              calc.enterNumber(extractNumber(), c);	// 调用calc的enterNumber方法
          else
              calc.enterOp(c);	//	否则调用calc对象的enterOp方法只输入操作码
          reset();
       }
       else if ( nump(c) && nbuf.length() < prec )	// if c a num 且在计算器精度范围内
       {  num = true;
          buildNumber(c);
       }
   }

   protected boolean nump(char c)
   {  return( c == '.' || Character.isDigit(c) );  }

   protected String extractNumber()			//	返回代表输入数的字符串
   {   return (nbuf.length() == 0) ?  "0"
              : nbuf.toString();
   }

   protected void buildNumber(char c)		//	将输入数存储到字符串缓冲区nbuf中
   {    int i = nbuf.length();
        if ( i == 0 && c == '0') return;     // ignore leading zeros
        if ( c == '.' )                      // at most one decimal point
        {    if ( ! before_point ) return;
             else before_point = false;
        }
        nbuf.append(c);						//	to end of string buffer   
   }

   protected void reset() 
   {    before_point = true;
        nbuf.setLength(0);
        num = false;
   }
   
   protected int inchar()				//	从标准输入中取下一个字符
      throws IOException
   {  return System.in.read(); }


   protected String prompt="Calc:  ";
   protected boolean errMode = false;
   protected String active;
   protected Calculator calc;
   protected String keys;         // keys recognized
   protected StringBuffer nbuf;   // buffer for input number

   protected int prec;            // max no of chars displayable
   protected boolean before_point = true;
   protected boolean num = false;
}