修改 Arraylist 中的所有值

Question

我的编程 I 课程有一个实验室，我们需要设计一个程序，该程序使用电阻的 ArrayList 来计算并联和串联电路的总电阻。对于并联电路，我需要将 ArrayList 中的每个项目更改为其倒数（1/项目）。我到了这一点，似乎无法找到为什么这是错误的以及可能的解决方法。谢谢。

**我得到的错误是“ArrayList 类型中的方法 get(int) 不适用于参数 (double)”，用于“resistances = 1 / resistances.get(index);”行**

-业务逻辑类-

import java.util.ArrayList;

/**
* The class Circuit gathers the resistances of a user-defined number of
* resistors for a user-defined type of circuit and displays the total
* resistance of the circuit for the main method of the Presentation class.
*/

public class Circuit {

    private double arrayListSize;

    public double n;

    public double sum;

    public double finalSum;

    public ArrayList<Double> resistances = new ArrayList<Double>();

    /**
     * @param initialPop
     *      user-defined initial population
     */
    public final void setArraySize(final double alSize) {
        arrayListSize = alSize;
    }

    public final double getArraySize() {
        return arrayListSize;
    }

    public final void setResistors(double alResistances) {
        for (n = 0; n < getArraySize(); n++) {
            resistances.add(alResistances);
        }
    }

    public  ArrayList<Double> getResistors() {
        return resistances;
    }

    public final void setPResistance(ArrayList<Double> resistances) {
        for (double index : resistances) {
            resistances = 1 / resistances.get(index);
        }
        sum = 0;
        for (double i : resistances) {
            sum =sum + i;
        }
        double finalSum = 1 / sum;

    }

    public final double getPResistance() {
        return finalSum;
    }
}

-演示类-

import java.util.Scanner;

/**
* The Class Presentation
*/
public class Presentation {

    /**
    * The main class uses the Circuit class and user input 
    * to calculate the total resistance of a circuit.
    * 
    * @param args
    *            command line arguments
    */
    public static void main(final String[] args) {
        Scanner keyboard = new Scanner(System.in);
        Circuit resistanceTotal = new Circuit();

        System.out.println("This program will calculate the"
                + " total resistance of either a parallel or "
                + " a series circuit.\n");

        System.out.println("Would you like to calculate the"
                + " resistance of a parallel circuit (1) or a"
                + " series circuit (2)?");
        int userChoice = keyboard.nextInt();

        System.out.println("How many resistors are there in the circuit?");
        resistanceTotal.setArraySize(keyboard.nextDouble());

        System.out.println("Enter resistance of resistor #" + (resistanceTotal.n + 1));
        resistanceTotal.setResistors(keyboard.nextDouble());
        resistanceTotal.getResistors();

        if (userChoice == 1) {
            resistanceTotal.setPResistance(resistanceTotal.getResistors());
            resistanceTotal.getPResistance();
        }

        if (userChoice != 1 & userChoice != 2) {
            System.out.println("You must enter 1 or 2!!!");
        }
        keyboard.close();
    }
}

Answer 1

您的错误在于 setPResistance 方法。 arrayList.get(i) 方法将int 值作为参数，您将位置的实际值传递给它，即double。

要将数组列表中的每个项目替换为其倒数，请更改方法，如下所示：

public final void setPResistance(ArrayList<Double> resistances) {
    for (int c = 0; c < resistances.size(); c++) {
        resistances.set(c, 1/resistances.get(c));
    }
}

set(int index, Double element) 方法的 Java 文档：

将此列表中指定位置的元素替换为 指定元素。