import java.util.ListIterator;import java.util.Stack;
public class CalStr { private String src;
/** * constructor * * @param srcthe string(expression) to calculate */ public CalStr(String src) { this.src = src; }
/** * calculate to get the result * * @return(double)result */ public double getResult() { String postfix = getPostfix(); Stack stk = new Stack(); // System.out.println(postfix); String parts[] = postfix.split(" +"); double result = 0; for (int i = 0; i < parts.length; i++) { char tmp = parts[i].charAt(0); if (!isOperator(tmp)) { stk.push(parts[i]); } else { double a = Double.parseDouble((String) stk.pop()); double b = Double.parseDouble((String) stk.pop()); // b is followed by a in the orignal expression result = calculate(b, a, tmp); stk.push(String.valueOf(result)); } } return result; }
/** * test if the character is an operator,such +,-,*,/ * * @param opthe character to test * @returntrue if op is an operator otherwise false */ private boolean isOperator(char op) { return (op == '+' || op == '-' || op == '*' || op == '/'); }
/** * calculate an expression such (a op b) * * @param anumber 1 * @param bnumber 2 * @param opthe operator * @return(double)(a op b) */ public double calculate(double a, double b, char op) { switch (op) { case '+': return a + b; case '-': return a - b; case '*': return a * b; case '/': return a / b; } return -1; }
/** * convert the suffix to postfix * * @returnthe postfix as a string */ private String getPostfix() { Stack stk = new Stack(); String postfix = new String(); char op; int i = 0; while (i < src.length()) { if (Character.isDigit(src.charAt(i)) || src.charAt(i) == '.') { postfix += " "; do { postfix += src.charAt(i++); } while ((i < src.length()) && (Character.isDigit(src.charAt(i)))); postfix += " "; }
else { switch (op = src.charAt(i++)) { case '(': stk.push("("); break;
case ')': while (stk.peek() != "(") { String tmp = (String) stk.pop(); postfix += tmp; if (tmp.length() == 1 && isOperator(tmp.charAt(0))) postfix += " "; } stk.pop(); postfix += " "; break;
case '+': case '-': while ((!stk.empty()) && (stk.peek() != "(")) { postfix += stk.pop() + " "; } stk.push(String.valueOf(new Character(op))); break;
case '*': case '/': while ((!stk.empty()) && ((stk.peek() == "*") || (stk.peek() == "/"))) { postfix += stk.pop() + " "; } stk.push(String.valueOf(new Character(op))); break; } } } ListIterator it = stk.listIterator(stk.size()); while (it.hasPrevious()) postfix += it.previous() + " "; return postfix.trim().replaceAll(" +//.", "."); }
/** * main function * * @param args */ public static void main(String args[]) { System.out.println(new CalStr("((1.5+6.000)*9+9.36)*(8+9-8*8+8*7)") .getResult()); }}
这个程序是可以编译直接运行的
("((1.5+6.000)*9+9.36)*(8+9-8*8+8*7)")
结果 691.74
