java - Java中的无限循环问题

Question

当我在这段代码的底部运行 for 循环时，我得到一个无限循环，每次使用 i 都会输出 if 语句中的输出 每次都会增加并且不会停止。我很确定这是一个小问题，我只是无法指出......

    import java.util.Scanner;

public class HW2johnson_pp1 {

    public static void main(String args[]) {

        Scanner keyboard = new Scanner(System.in);

        System.out.printf("Please enter the species with the higher" + 
                          " population first\n");
        System.out.printf("Enter the name of your first species ");
        String Species1 = keyboard.nextLine();
        System.out.printf("Enter the species' population: ");
        int Pop1 = keyboard.nextInt();
        System.out.printf("Enter the species' growth rate: ");
        int Growth1 = keyboard.nextInt();

        System.out.printf("Enter the name of your second species: ");
        String Species2 = keyboard.nextLine();
        System.out.printf("Enter the species' population: ");
        int Pop2 = keyboard.nextInt();
        System.out.printf("Enter the species' growth rate: ");
        int Growth2 = keyboard.nextInt();

        if (Pop2 > Pop1) {
            System.out.printf("The first population must be higher. \n");
            System.exit(0);
        }


        Species input1 = new Species();
        input1.name = Species1;
        input1.population = Pop1;
        input1.growthRate = Growth1;

        Species input2 = new Species();
        input2.name = Species2;
        input2.population = Pop2;
        input2.growthRate = Growth2;

        if ((input1.predictPopulation(1) - input2.predictPopulation(1)) <= 
            (input1.predictPopulation(2) - input2.predictPopulation(2))){

            System.out.printf(Species2 + " will never out-populate " + 
                              Species1 + "\n");
        }
        else {

            for (int i = 0; input2.predictPopulation(i) <= 
                            input1.predictPopulation(i); i++) {

                if (input2.predictPopulation(i) == input1.predictPopulation(i)) {
                    System.out.printf(" will out-populate \n");
                }
            }
        }
    }
}

<小时/>

public int predictPopulation(int years)
        {
            int result = 0;
            double populationAmount = population;
            int count = years;
            while ((count > 0) && (populationAmount > 0))
            {
                populationAmount = (populationAmount +
                              (growthRate / 100) * populationAmount);
                count--;
            }
            if (populationAmount > 0)
                result = (int)populationAmount;

            return result;
        }

Answer 1

这个:

        if (Pop2 > Pop1) {
            Species2 = Species1;
            Pop2 = Pop1;
            Growth1 = Growth2;
        }

没有意义。显然，您的目的是“交换”两个群体的值，但相反，您只是使两个群体相同，因此对于 years 的任何值, predictPopulation(years)两个对象都是相同的。

<小时/>

编辑添加:此测试:

        if ((input1.predictPopulation(1) - input2.predictPopulation(1)) < 
            (input1.predictPopulation(2) - input2.predictPopulation(2)))

不是判断物种 2 最终是否会超越物种 1 的有效方法。如果物种 2 具有更大的比例增长率 ( growthRate )，那么它最终将超越物种 1，甚至如果在最初几年，它的绝对增长率较低。 (这仅与您的无限循环无关 - Dampsquid 指出，如果您使用 <= 而不是 < ，您将不会有无限循环 - 但这是您需要解决的问题。)