java - 代码似乎跳过了 if 或 for 循环

Question

1. 当我输入满足所有要求且不会触发任何错误的输入时，程序会在最后一次输入后退出，就像跳过 for 或 if 循环。

2. 此外，在 System.out.printf("输入您的第二个物种的名称:"); 之后，它不会允许任何输入，它只是跳到下一个提示。我不知道为什么会这样。上面询问第一个物种信息的部分工作正常。

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/>

这用于predictPopulation():

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

1. 这是因为在物种 2 超过物种 1 后，您永远不会打印任何内容，除非在非常特殊的情况下，物种 2 和物种 1 在某一年的人口完全相同。

2. 这是因为，当您输入物种 1 的增长率时，您输入一个整数，然后按 Enter。 keyboard.nextInt() 吞下整数，但将换行符保留在输入缓冲区上，因此后续的 keyboard.nextLine() 认为有一个空行在等待它.