5.1封装与测试

源代码：/** 采用算符优先算法计算表达式
* @param
*  String ex : 表达式的字符串；
* @return
*  String 类型的计算结果；
* 运算符栈operatorList按优先级存放运算符；运算数栈operandList存放运算数；
*/
public String evaluateExpression(String ex){
 // 在表达式首尾加上字符‘#‘以方便比较运算符
 StringBuffer exB = new StringBuffer(ex);
 exB.insert(0,‘#‘);
 exB.append(‘#‘);
 ex = exB.toString();    

 StringBuffer operandBuffer = new StringBuffer(); // 运算数的字符缓冲区
 java.util.LinkedList<BigDecimal> operandList = new LinkedList<BigDecimal>();
 java.util.LinkedList<String> operatorList = new LinkedList<String>();    

 int count = 1; // 从ex的序号为1开始，即‘#’后
 int num = 0 ; // 调试用
 operatorList.addLast("#");
 while(count < ex.length()){
  String ch = String.valueOf(ex.charAt(count));    

  if(Pattern.matches("[0-9//.]",ch) // 当前字符如果是数字或.就把它放到运算数缓冲区
  ||(ch.equals("-")  // "-"看成是负号的条件：在表达式的首位或在”（“之后；
  &&(count ==1 || ex.charAt(count-1) == ‘(‘))){
   operandBuffer.append(ch);
   System.out.println(ch+"属于运算数："); // 调试用
   ++count;
  }    

  else{
   // 把运算数放入栈
   if(Pattern.matches("[//+//-//*/////)//#]",ch) && operandBuffer.length() != 0){
    operandList.addLast(new BigDecimal(Double.valueOf(operandBuffer.toString()).toString()));    

    System.out.println("序号"+(++num)+"："+operandBuffer.toString()); // 调试用
    System.out.println("");    

    operandBuffer.delete(0,operandBuffer.length());
   }    

   System.out.println(ch+"属于运算符："); // 调试用
   System.out.println("");    

   // 比较运算符，并根据它进行计算
   switch(compareOperator(operatorList.getLast(),ch)){
    // ch优先级高，将ch压入运算符栈
    case ‘<‘ :
     operatorList.addLast(ch);
     ++count;
     break;
    // 优先级相等时，去掉（）或前后的#；
    case ‘=‘ :
     operatorList.removeLast();
     ++count;
     break;
    // ch优先级低，从运算数栈取出两个数，从运算符栈取出运算符，进行计算其结果放入运算数栈；
    case ‘>‘ :
     BigDecimal b = operandList.removeLast();
     BigDecimal a = operandList.removeLast();
     String curOperator = operatorList.removeLast();    

     try{
      operandList.addLast(operate(a,curOperator,b));
     }catch(ArithmeticException e){
      return "除数不能为0！";
     }
     break;
    // 运算符输入错误的处理：终止计算，在屏幕显示input error!
    default :
     return "输入有误！";
   }
  }
 }//End 0f while
 for(BigDecimal e : operandList)  // 调试用
  System.out.println(e.toString());    

 return operandList.getLast().toString();
}    

/** 比较前后运算符的优先级 */
public char compareOperator(String operator1,String operator2){
 char result = ‘/u0000‘; // 局部内部类的实例方法的局部变量能自动初始化为‘/u0000‘吗？不得行！！！
 char o1 = operator1.charAt(0);
 char o2 = operator2.charAt(0);    

 switch(o1){
  case ‘+‘:
   switch(o2){
    case ‘+‘:
     result = ‘>‘;
     break;
    case ‘-‘:
     result = ‘>‘;
     break;
    case ‘*‘:
     result = ‘<‘;
     break;
    case ‘/‘:
     result = ‘<‘;
     break;
    case ‘(‘:
     result = ‘<‘;
     break;
    case ‘)‘:
     result = ‘>‘;
     break;
    case ‘#‘:
     result = ‘>‘;
     break;
   }
   break; // 跳出case ‘+‘;
  case ‘-‘:
   switch(o2){
    case ‘+‘:
     result = ‘>‘;
     break;
    case ‘-‘:
     result = ‘>‘;
     break;
    case ‘*‘:
     result = ‘<‘;
     break;
    case ‘/‘:
     result = ‘<‘;
     break;
    case ‘(‘:
     result = ‘<‘;
     break;
    case ‘)‘:
     result = ‘>‘;
     break;
    case ‘#‘:
     result = ‘>‘;
     break;
   }
   break; // 跳出case ‘-‘;
  case ‘*‘:
   switch(o2){
    case ‘+‘:
     result = ‘>‘;
     break;
    case ‘-‘:
     result = ‘>‘;
     break;
    case ‘*‘:
     result = ‘>‘;
     break;
    case ‘/‘:
     result = ‘>‘;
     break;
    case ‘(‘:
     result = ‘<‘;
     break;
    case ‘)‘:
     result = ‘>‘;
     break;
    case ‘#‘:
     result = ‘>‘;
     break;
   }
   break; // 跳出case ‘*‘;
  case ‘/‘:
   switch(o2){
    case ‘+‘:
     result = ‘>‘;
     break;
    case ‘-‘:
     result = ‘>‘;
     break;
    case ‘*‘:
     result = ‘>‘;
     break;
    case ‘/‘:
     result = ‘>‘;
     break;
    case ‘(‘:
     result = ‘<‘;
     break;
    case ‘)‘:
     result = ‘>‘;
     break;
    case ‘#‘:
     result = ‘>‘;
     break;
   }
   break; // 跳出case ‘/‘;
  case ‘(‘:
   switch(o2){
    case ‘+‘:
     result = ‘<‘;
     break;
    case ‘-‘:
     result = ‘<‘;
     break;
    case ‘*‘:
     result = ‘<‘;
     break;
    case ‘/‘:
     result = ‘<‘;
     break;
    case ‘(‘:
     result = ‘<‘;
     break;
    case ‘)‘:
     result = ‘=‘;
     break;
    case ‘#‘:
     result = ‘?‘; // （后不能是#，如果是则是错误输入；
     break;
   }
   break; // 跳出case ‘(‘;
  case ‘)‘:
   switch(o2){
    case ‘+‘:
     result = ‘>‘;
     break;
    case ‘-‘:
     result = ‘>‘;
     break;
    case ‘*‘:
     result = ‘>‘;
     break;
    case ‘/‘:
     result = ‘>‘;
     break;
    case ‘(‘:
     result = ‘?‘; // )后不能接（；
     break;
    case ‘)‘:
     result = ‘>‘;
     break;
    case ‘#‘:
     result = ‘>‘;
     break;
   }
   break; // 跳出case ‘)‘;
  case ‘#‘:
   switch(o2){
    case ‘+‘:
     result = ‘<‘;
     break;
    case ‘-‘:
     result = ‘<‘;
     break;
    case ‘*‘:
     result = ‘<‘;
     break;
    case ‘/‘:
     result = ‘<‘;
     break;
    case ‘(‘:
     result = ‘<‘;
     break;
    case ‘)‘:
     result = ‘?‘; // #后不能接）；
     break;
    case ‘#‘:
     result = ‘=‘;
     break;
   }
   break; // 跳出case ‘#‘;
 }// End Of switch    

 return result;
}    

/** 根据运算符进行二元计算，
* @param
*  BigDecimal类型 a ? b
* @return：
*  BigDecimal类型的结果
*/
public BigDecimal operate(BigDecimal a,String operator,BigDecimal b){
  final int DEF_DIV_SCALE = 20;
  BigDecimal result = null;    

 switch(operator.charAt(0)){
  case ‘+‘:
   result = a.add(b);
   break;
  case ‘-‘:
   result = a.subtract(b);
   break;
  case ‘*‘:
   result = a.multiply(b);
   break;
  case ‘/‘:
   result = a.divide(b,DEF_DIV_SCALE,BigDecimal.ROUND_HALF_UP);
   break;
 }
 return result;
}