英文:
How do I get the Scanner in java to read a string?
问题
import java.util.*;
public class Main {
public static void main(String[] args) {
String input;
Scanner scan = new Scanner(System.in);
System.out.println("Enter your age, or enter 'q' to quit the program.");
input = scan.next();
if (input.equalsIgnoreCase("q")) {
return;
}
int age = Integer.parseInt(input);
System.out.println("Your age is " + age);
}
}
英文:
How would I get my program to quit when the user enters q?
Is there something wrong with the scanner?
My code
import java.util.*;
public class Main{
public static void main(String []args){
int age;
Scanner scan = new Scanner(System.in);
System.out.println("Enter your age, or enter 'q' to quit the program.");
age = scan.nextInt();
if(age.equals("q") || age.equals("Q")){
return 0;
}
System.out.println("Your age is " + age);
}
}
答案1
得分: 0
我在你的代码中主要看到两个问题：
- 代码缺少一个循环来重复询问年龄。有许多种方法（
for、while、do-while）可以编写循环，但我认为对于这种情况，do-while是最合适的，因为它始终至少执行do块中的语句一次。 age的类型是int，因此无法与字符串进行比较，例如你的代码age.equals("q")是不正确的。处理这种情况的一种好方法是将输入存储在类型为String的变量中，并在需要时检查其值，以确定是否应该允许/禁止处理它（例如尝试将其解析为int）。
注意，当你尝试解析一个无法解析为 int 的字符串（例如 "a"）时，会得到一个 NumberFormatException，你需要处理它（例如显示错误消息，更改某些状态等）。
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
int age;
String input;
Scanner scan = new Scanner(System.in);
boolean valid;
do {
// 假设输入是有效的
valid = true;
System.out.print("输入你的年龄，或输入 'q' 退出程序: ");
input = scan.nextLine();
if (!(input.equals("q") || input.equals("Q"))) {
try {
// 尝试将输入解析为整数
age = Integer.parseInt(input);
System.out.println("你的年龄是 " + age);
} catch (NumberFormatException e) {
System.out.println("无效输入");
// 将 valid 的值更改为 false
valid = false;
}
}
} while (!valid || !(input.equals("q") || input.equals("Q")));
}
}
一个示例运行：
输入你的年龄，或输入 'q' 退出程序: a
无效输入
输入你的年龄，或输入 'q' 退出程序: 12.5
无效输入
输入你的年龄，或输入 'q' 退出程序: 14
你的年龄是 14
输入你的年龄，或输入 'q' 退出程序: 56
你的年龄是 56
输入你的年龄，或输入 'q' 退出程序: q
英文:
I can see mainly two problems in your code:
- It lacks a loop to repeat asking for age again. There can be many ways (
for,while,do-while) to write a loop but I finddo-whilemost appropriate for such a case as it always executes the statements within thedoblock at least once. ageis of type,intand therefore it can not be compared with a string e.g. your code,age.equals("q")is not correct. A good way to handle such a situation is to get the input into a variable of type,Stringand check the value if it should allow/disallow processing it (e.g. trying to parse it into anint).
Note that when you try to parse a string which can not be parsed into an int (e.g. "a"), you get a NumberFormatException which you need to handle (e.g. show an error message, change some state etc.).
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
int age;
String input;
Scanner scan = new Scanner(System.in);
boolean valid;
do {
// Start with the assumption that input will be valid
valid = true;
System.out.print("Enter your age, or enter 'q' to quit the program: ");
input = scan.nextLine();
if (!(input.equals("q") || input.equals("Q"))) {
try {
// Try to parse input into an int
age = Integer.parseInt(input);
System.out.println("Your age is " + age);
} catch (NumberFormatException e) {
System.out.println("Invalid input");
// Change the value of valid to false
valid = false;
}
}
} while (!valid || !(input.equals("q") || input.equals("Q")));
}
}
A sample run:
Enter your age, or enter 'q' to quit the program: a
Invalid input
Enter your age, or enter 'q' to quit the program: 12.5
Invalid input
Enter your age, or enter 'q' to quit the program: 14
Your age is 14
Enter your age, or enter 'q' to quit the program: 56
Your age is 56
Enter your age, or enter 'q' to quit the program: q
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