Question

程序无法识别我输入了gerbil.foodTypes的值（gerbil.foodName.length的值为0。为什么？

class Gerbil {
public int foodTypes;
public String[] foodName = new String[foodTypes];
}
public class mainmethod {
public static void main(String args[]) {
    Scanner keyboard = new Scanner(System.in);
    Gerbil gerbil = new Gerbil();
    System.out.println("How many types of food do the gerbils eat?");
    gerbil.foodTypes = keyboard.nextInt();
    for (int x = 0; x < gerbil.foodTypes ; x++) { 
        System.out.println("Enter the name of food item " + (x+1));
        gerbil.foodName[x] = keyboard.nextLine();
        keyboard.nextLine();
        System.out.println("Maximum consumed per gerbil:");
        gerbil.foodMax[x] = keyboard.nextInt();
    }

Answer 1

public int foodTypes;
public String[] foodName = new String[foodTypes];

在评估foodTypes时，

new String[foodTypes]为0，因此foodName始终为零长度数组。

可能添加一个带foodTypes的构造函数。

Gerbil gerbil = new Gerbil(keyboard.nextInt());

Answer 2

构造类时，数组'foodName'的启动长度为零。这样做的原因是当你声明一个整数，例如。public int foodTypes'时，所有编译器看到的都是public int foodTypes = 0;

初始化后无法调整数组的大小，因此无法“重置”数组的大小。

我会添加一个构造函数，它从输入中获取一个数字并将其分配给foodTypes，因此它不是0.

这是一些未经测试的代码：

class Gerbil {
public int foodTypes;
public String[] foodName;

public Gerbil(int num){
    this.foodTypes = num;
    this.foodName = new String[foodTypes];
}
}
public class Assignment4 {
public static void main(String args[]) {
    Scanner keyboard = new Scanner(System.in);
    System.out.println("How many types of food do the gerbils eat?");
        Gerbil gerbil = new Gerbil(keyboard.nextInt());
    for (int x = 0; x < gerbil.foodTypes ; x++) { 
        System.out.println("Enter the name of food item " + (x+1));
        gerbil.foodName[x] = keyboard.nextLine();
        keyboard.nextLine();
        System.out.println("Maximum consumed per gerbil:");
        gerbil.foodMax[x] = keyboard.nextInt();
    }

Here是有关数组的更多文档。

班级不会识别用户输入？

2 个答案: