Question

java里使用面向对象的思想编写一个计算器类（Calculator），可以实现两个数的加、减、乘、除运算

Answer 1

package calculate;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Calculator {
    public static void main(String[] args) {
        System.out.println(calculate("x=1+2+3+4,y=1*2*3*4"));
        System.out.println(new Calculator("2*2*3.1415926"));
        System.out.println(new Calculator("(10+10)*10-10/10"));
        System.out.println(new Calculator("2^10"));
        System.out.println(new Calculator("10!"));
        System.out.println(new Calculator("(2*(3+2))!"));
    }
    public static String calculate(String exp) {
        return new Calculator(exp).calculate();
    }
    private static String regex_num = "(\\d+(\\.\\d+)?)";
    private String exp;
    private String result;
    public Calculator(String exp) {
        this.exp = exp;
        this.result = exp.replaceAll("\\s+", "");
    }
    public String calculate() {
        calculateSub();
        calcuateFactorial();
        calcuate("\\^", Handler.Power);
        calcuate("\\*", Handler.Multiply);
        calcuate("/", Handler.Divide);
        calcuate("\\+", Handler.Add);
        calcuate("\\-", Handler.Subtract);
        return result;
    }
    private void calculateSub() {
        Pattern pattern = Pattern.compile("\\(([^\\(\\)]+)\\)");
        Matcher matcher = pattern.matcher(result);
        while (matcher.reset(result).find()) {
            updateResult(matcher, calculate(matcher.group(1)));
        }
    }
    private void calcuateFactorial() {
        Pattern pattern = Pattern.compile(regex_num + "!");
        Matcher matcher = pattern.matcher(result);
        while (matcher.reset(result).find()) {
            BigDecimal decimal = new BigDecimal(result.substring(0, result.length() - 1));
            if (decimal.toString().indexOf(".") > -1) {
                throw new RuntimeException("when a!, a must is a integer");
            }
            updateResult(matcher, factorial(decimal.intValue()));
        }
    }
    public static BigInteger factorial(int num) {
        if (num < 1) {
            throw new RuntimeException("num can't < 1");
        }
        if (num == 1) {
            return BigInteger.ONE;
        } else {
            BigInteger bigInteger = BigInteger.valueOf(num);
            return bigInteger.multiply(factorial(num - 1));
        }
    }
    private void calcuate(String regex_sign, Handler handler) {
        Pattern pattern = Pattern.compile(regex_num + regex_sign + regex_num);
        Matcher matcher = pattern.matcher(result);
        while (matcher.reset(result).find()) {
            String[] split = matcher.group().split(regex_sign);
            BigDecimal decimal = new BigDecimal(split[0]);
            BigDecimal decimal2 = new BigDecimal(split[1]);
            updateResult(matcher, handler.calculate(decimal, decimal2));
        }
    }
    private void updateResult(Matcher matcher, Object value) {
        result = result.substring(0, matcher.start()) + value + result.substring(matcher.end());
    }
    public String toString() {
        return exp + "=" + calculate();
    }
    public interface Handler {
        public BigDecimal calculate(BigDecimal decimal, BigDecimal decimal2);
        public static final Handler Add = new Handler() {
            public BigDecimal calculate(BigDecimal decimal, BigDecimal decimal2) {
                return decimal.add(decimal2);
            }
        };
        public static final Handler Subtract = new Handler() {
            public BigDecimal calculate(BigDecimal decimal, BigDecimal decimal2) {
                return decimal.subtract(decimal2);
            }
        };
        public static final Handler Multiply = new Handler() {
            public BigDecimal calculate(BigDecimal decimal, BigDecimal decimal2) {
                return decimal.multiply(decimal2);
            }
        };
        public static final Handler Divide = new Handler() {
            public BigDecimal calculate(BigDecimal decimal, BigDecimal decimal2) {
                if (decimal2.equals(BigDecimal.ZERO)) {
                    throw new RuntimeException("when a / b, b can't be zero");
                }
                return decimal.divide(decimal2);
            }
        };
        public static final Handler Power = new Handler() {
            public BigDecimal calculate(BigDecimal decimal, BigDecimal decimal2) {
                if (decimal2.toString().indexOf(".") > -1) {
                    throw new RuntimeException("when a ^ b, b must is a integer");
                }
                return decimal.pow(decimal2.intValue());
            }
        };
    }
}

刚才的用到了一些工具类，现在把它去掉

追问

看不懂呀，我只是初学 JAVA，能不能按我的请求做下，谢谢了

追答

哦，你是初学啊，我还以为你要做一个计算字符串的计算器呢，我明白了，马上写一个简单的。

public class Calculator {
public int add(int a, int b) {
return a + b;
}
public int subtract(int a, int b) {
return a - b;
}
public int multiply(int a, int b) {
return a * b;
}
public int divide(int a, int b) {
return a / b;
}
}

追问

辛苦了，不过还是看不懂，我现在才学到类和对象。。。。。

追答

。。。英文看不懂吗。。。就是加减乘除啊。。。