二次读取法 [英] Quadratic Read Method

问题描述

我必须为一个二次类编写一个read方法，其中以ax ^ 2 + bx + c的形式输入一个二次数.该类的描述是这样的:

I have to write a read method for a quadratic class where a quadratic is entered in the form ax^2 + bx + c. The description for the class is this:

添加一个read方法，该方法要求用户提供标准格式的方程式，并正确设置三个实例变量. (因此，如果用户键入3x ^ 2--x，则将实例变量设置为3，-1和0).这将需要您之前完成的字符串处理.显示输入的实际方程式，并正确标记为预期输出.

Add a read method that asks the user for an equation in standard format and set the three instance variables correctly. (So if the user types 3x^2 - x, you set the instance variables to 3, -1, and 0). This will require string processing you have done before. Display the actual equation entered as is and properly labeled as expected output.

我能够通过使用字符串操作和if else语句来完成ax ^ 2部分.但是我不确定如何处理方程式的bx和c部分，因为符号可能在bx和c前面.这是我做方法的ax ^ 2部分的方法.

I was able to do the ax^2 part by using string manipulation and if else statements. But I am not sure how to do the bx and c parts of the equation because of the sign that could be in front of bx and c. Here is how I did the ax^2 part of the method.

public void read()
{
    Scanner keyboard = new Scanner(System.in);
    System.out.println("Please enter a quadratic equation in standard format.");
    String formula = keyboard.next();
    String a = formula.substring(0, formula.indexOf("x^2"));
    int a2 = Integer.parseInt(a);
    if (a2 == 0)
    {
        System.out.println("a = 0");
    }
    else if (a2 == 1)
    {
        System.out.println("a = 1");
    }
    else
    {
        System.out.println("a = " + a2);
    }
 }

随意编写任何代码作为示例. 任何帮助将不胜感激.

Feel free to write any code as an example. Any help would be greatly appreciated.

推荐答案

import java.util.regex.Matcher;
import java.util.regex.Pattern;


public class Mini {

    public static void main(String[] args) {
        int a = 0;
        int b = 0;
        int c = 0;

    String formula = " -x^2 + 6x - 5";
    formula = formula.replaceAll(" ", "");

    if (!formula.startsWith("+") && !formula.startsWith("-"))
        formula = "+" + formula;

        String exp = "^((.*)x\\^2)?((.*)x)?([\\+\\s\\-\\d]*)?$";
        Pattern p = Pattern.compile(exp);
        Matcher m = p.matcher(formula);

        System.out.println("Formula is " + formula);
        System.out.println("Pattern is " + m.pattern());

        while (m.find()) {
            a = getDigit(m.group(2));
            b = getDigit(m.group(4));
            c = getDigit(m.group(5));
        }

        System.out.println("a: " + a + " b: " + b + " c: " + c);

    }

    private static int getDigit(String data) {
        if (data == null) {
            return 0;
        } 
        else 
        {

            if (data.equals("+"))
            {
                return 1;
            }
            else if (data.equals("-"))
            {
                return -1;
            }
            else
            {
                try
                {
                    int num = (int) Float.parseFloat(data);
                    return num;
                }
                catch (NumberFormatException ex)
                {
                    return 0;
                }
            }
        }
    }
}

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