如何从 main 方法中获取值以用于另一个 class？

Question

我目前正在编写一个程序来获取用户对多项式系数和次数的输入，然后将这些输入转换为多项式。在我的主要方法中，我使用扫描仪获取一行字符串，然后将其转换为双精度数组。但是，我需要在另一个 class 中使用这个双数组的值，但似乎无法做到。我已经坚持了一段时间，甚至在研究之后我似乎仍然无法理解它。

PolynomialDemo.java

public class PolynomialDemo  {
public static int degree;
public static double[] numbers;

public static void main(String[] args) {

    Scanner scan = new Scanner(System.in);
    Scanner scanner = new Scanner(System.in);
    System.out.print("Enter the degree of the first polynomial -> ");
    degree = scan.nextInt();

    System.out.print("Enter its coefficients in order of descending powers -> ");
    String deg = scanner.nextLine();
    String[] numbersStr = deg.split(" ");
    double[] numbers = new double[ numbersStr.length ];
    for ( int i = 0; i < numbersStr.length; i++ )
    {
        numbers[i] = Integer.parseInt( numbersStr[i] );
    }

Polynomial.java

public class Polynomial implements PolyEval  {

private double[] coeffs;
private int degree;


public Polynomial() {
//creates polynomial 0
}

public Polynomial(double[] c) throws IllegalArgumentException{
//obtain coefficients
}

@Override
public int degree() {
 //return degree
}

@Override
public String toString() {
    //build polynomial

}}

Polynomial.java 是我需要获取的值 class 。当我尝试这样做时，值总是 returns 'null' 当它到达时多项式 class。我被困住了，不知道从这里去哪里。感谢您的帮助！

Answer 1

您应该实例化一个 Polinomial 对象并设置您需要的值。

public class PolynomialDemo  {
public static int degree;
public static double[] numbers;

public static void main(String[] args) {

    //Create a Polynomial object
    Polynomial pol = new Polynomial();

    Scanner scan = new Scanner(System.in);
    Scanner scanner = new Scanner(System.in);
    System.out.print("Enter the degree of the first polynomial -> ");
    degree = scan.nextInt();

    System.out.print("Enter its coefficients in order of descending powers -> ");
    String deg = scanner.nextLine();
    String[] numbersStr = deg.split(" ");
    double[] numbers = new double[ numbersStr.length ];
    for ( int i = 0; i < numbersStr.length; i++ )
    {
        numbers[i] = Integer.parseInt( numbersStr[i] );
    }


    //Set values
    pol.setDegree(degree);
    pol.setCoefficients(numbers);

}

您需要在 Polynomial class.

中定义 setDegree(int degree) 和 setCoefficients(double [] coeff)

Setter、构造函数等是 Java 的基础。尝试寻找教程或阅读文档。另外，尝试模块化您的代码。

如何从 main 方法中获取值以用于另一个 class？

How do you obtain a value from the main method to use in another class?

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