Question

我知道这段代码编写得非常糟糕（Java和编程的第一天），但我正在编写一个Java代码，它将从用户（骰子）获取输入并从该骰子中生成一个随机数。我添加了一个while循环来询问用户是否想要重新启动程序，但是每次运行它都会告诉我在输入任何内容之前它是无效的输入。请帮忙。

import java.util.Scanner;
import java.util.Random;
public class Java {
public static void main(String args[]){
    Scanner input = new Scanner(System.in);
    String restartChoice = "y";
    while (restartChoice == "y" || restartChoice == "Y"){
        int choice;
        System.out.println("Please choose which dice you would like to                       roll. 4/6/12 ");
        choice = input.nextInt();
        while (choice != 4 && choice != 6 && choice != 12){
            System.out.println("That is not a valid input, please try again... ");
            choice = input.nextInt();   
        }
        Random rand = new Random(); 
        int value = rand.nextInt(choice) + 1;
        System.out.print("You chose to roll the ");
        System.out.print(choice);
        System.out.print(" sided dice. The number is ");
        System.out.println(value);
        System.out.println("Would you like to restart? Y/N ");
        restartChoice = input.nextLine();
        while (restartChoice != "y" && restartChoice != "n" && restartChoice != "y" && restartChoice != "n"){
            System.out.println("That is not a valid input. Please try again. ");
            restartChoice = input.nextLine();
        }
    }
}

}

Answer 1

Scanner#nextInt()不会使用换行符，导致该字符被传递到循环

while (restartChoice != "y" && restartChoice != "n" && restartChoice != "y" && restartChoice != "n"){
            System.out.println("That is not a valid input. Please try again. ");
            restartChoice = input.nextLine();
}

在每个nextLine语句后添加nextLine语句以使用此换行符。

choice = input.nextInt();
input.nextLine();

==运算符也会比较对象引用。使用String#equals：

while (restartChoice.equals("y") || restartChoice.equals("Y")) {

要防范NullPointerException，您可以先放置String字面值。此外，equalsIgnoreCase可用于提供更短的if语句表达式：

while ("y".equalsIgnoreCase(restartChoice)) {

while语句表达式需要进行此更改。

Answer 2

使用String.equals（otherString）

字符串是对象，而不是基元。您目前正在比较字符串的地址。

为什么我的Java代码不起作用？

2 个答案: