expressioncalculator.java

生产者消费者程序 非常好用的程序 生产者消费者程序 非常好用的程序

/*
 * Created on 2007-7-12
 */
package willishz.soho.arithmetic;

import java.util.ArrayList;
import java.util.Scanner;

/**
 * calculate an expression(end with "=", decimal supported, brackets unsupported).
 * @author willishz
 */
public class ExpressionCalculator {

    public static final char PLUS = '+';
    public static final char SUBTRACT = '-';
    public static final char MULTIPLE = '*';
    public static final char DIVIDE = '/';
    public static final char DECIMAL = '.';
    public static final char EQUAL = '=';
    
    public static final String PLUS_STR = "+";
    public static final String SUBTRACT_STR = "-";
    public static final String MULTIPLE_STR = "*";
    public static final String DIVIDE_STR = "/";
    
    /**
     * interpret expression string to units.
     * @param expression
     * @return
     */
    public static String interpret(String expression) {
        ArrayList explist = new ArrayList();
        int flg = 0; // flag to divide expression units
        StringBuffer sb = new StringBuffer();
        char[] expChars = expression.toCharArray();
        // expression string to units
        for (int i = 0; i < expChars.length; i++) {
            // expression divided by operators
            if (expChars[i] == ExpressionCalculator.EQUAL || expChars[i] == ExpressionCalculator.PLUS || expChars[i] == ExpressionCalculator.SUBTRACT || expChars[i] == ExpressionCalculator.MULTIPLE || expChars[i] == ExpressionCalculator.DIVIDE) {
                // paste digits of number between each two segments
                for (int j = flg; j < i; j++) {
                    sb.append(expChars[j]);
                    flg = i + 1;
                }
                // sucess divide a unit
                explist.add(sb.toString());
                // expression end with "=", paste last digits of number
                if (expChars[i] != ExpressionCalculator.EQUAL) { 
                    explist.add(String.valueOf(expChars[i]));
                }
                sb = new StringBuffer();
            }
        }
        // calculate this expression units
        return ExpressionCalculator.calculate(explist);
    }
    
    /**
     * calculate all units.
     * @param explist
     * @return
     */
    public static String calculate(ArrayList explist) {
        do {
            int operatorIndex = -1; // operator location
            // count operator, first multiple and divide
            if (explist.indexOf(ExpressionCalculator.PLUS_STR) > 0 && explist.indexOf(ExpressionCalculator.DIVIDE_STR) > 0) { // both
                operatorIndex = Math.min(explist.indexOf(ExpressionCalculator.PLUS_STR), explist.indexOf(ExpressionCalculator.DIVIDE_STR));
            } else if ((explist.indexOf(ExpressionCalculator.PLUS_STR) > 0 && explist.indexOf(ExpressionCalculator.DIVIDE_STR) < 0)) { // multiple only
                operatorIndex = explist.indexOf(ExpressionCalculator.PLUS_STR);
            } else if ((explist.indexOf(ExpressionCalculator.PLUS_STR) < 0 && explist.indexOf(ExpressionCalculator.DIVIDE_STR) > 0)) { // divide only
                operatorIndex = explist.indexOf(ExpressionCalculator.DIVIDE_STR);
            }
            
            //  finish counting multiple or divide operator
            if (operatorIndex > 0) { // do have multiple or divide operator
                explist = execute(explist, operatorIndex); // multiple or divide operation
                continue; // continue calculate
            }
            
            // no multiple or divide operation, count plus and subtract operator
            if (explist.indexOf(ExpressionCalculator.PLUS_STR) > 0 && explist.indexOf(ExpressionCalculator.SUBTRACT_STR) > 0) { // both
                operatorIndex = Math.min(explist.indexOf(ExpressionCalculator.PLUS_STR), explist.indexOf(ExpressionCalculator.SUBTRACT_STR));
            } else if ((explist.indexOf(ExpressionCalculator.PLUS_STR) > 0 && explist.indexOf(ExpressionCalculator.SUBTRACT_STR) < 0)) { // plus only
                operatorIndex = explist.indexOf(ExpressionCalculator.PLUS_STR);
            } else if ((explist.indexOf(ExpressionCalculator.PLUS_STR) < 0 && explist.indexOf(ExpressionCalculator.SUBTRACT_STR) > 0)) { // substract only
                operatorIndex = explist.indexOf(ExpressionCalculator.SUBTRACT_STR);
            }
            
            //  finish counting plus or subtract operator
            if (operatorIndex > 0) { // do have plus or subtract operator
                explist = execute(explist, operatorIndex); // plus or subtract operation
                continue; // continue calculate
            }
            
            // no operators
        return explist.get(0).toString(); // return result
        } while(true);
    }
    
    /**
     * calculate two units.
     * @param explist
     * @return
     */
    public static ArrayList execute(ArrayList explist, int operatorIndex) {
        double unit1 = Double.valueOf(explist.get(operatorIndex - 1).toString()).doubleValue(); // get factor1
        double unit2 = Double.valueOf(explist.get(operatorIndex + 1).toString()).doubleValue(); // get factor2
        char operator = explist.get(operatorIndex).toString().charAt(0); // get operator
        // estimate operator, do calculate, then rebuild arraylist
        switch (operator) {
        case ExpressionCalculator.PLUS:
            explist.set(operatorIndex - 1, String.valueOf(unit1 + unit2));
            explist.remove(operatorIndex + 1);
            explist.remove(operatorIndex);
            break;
        case ExpressionCalculator.SUBTRACT:
            explist.set(operatorIndex - 1, String.valueOf(unit1 - unit2));
            explist.remove(operatorIndex + 1);
            explist.remove(operatorIndex );
            break;
        case ExpressionCalculator.MULTIPLE:
            explist.set(operatorIndex - 1, String.valueOf(unit1 * unit2));
            explist.remove(operatorIndex + 1);
            explist.remove(operatorIndex);
            break;
        case ExpressionCalculator.DIVIDE:
            explist.set(operatorIndex - 1, String.valueOf(unit1 / unit2));
            explist.remove(operatorIndex + 1);
            explist.remove(operatorIndex);
            break;
        }
        return explist;
    }
    
    public static void main(String[] args) {
        System.out.print("请输入一个表达式以 \"=\" 结束(中间不加空格, 支持小数, 不支持括号): ");
        Scanner sc = new Scanner(System.in); // from console
        System.out.println(ExpressionCalculator.interpret(sc.next()));
        System.exit(0);
    }
}