英文:
How to check if userInput is an int
问题
import java.util.*;
public class ForLoopPractice {
public static void main(String[]args) {
Scanner scnr = new Scanner(System.in);
final int MAX_VALUE;
System.out.println("打印偶数值");
System.out.print("最大值：");
MAX_VALUE = scnr.nextInt();
for (int i=0; i < MAX_VALUE; i++) {
if (i % 2 == 0) {
System.out.println(i + " ");
}
}
while (!scnr.hasNextInt()) {
System.out.println("无效的值");
scnr.next();
}
System.out.println();
System.out.println("打印一定范围的值");
System.out.print("第一个值：");
int firstVal = scnr.nextInt();
System.out.print("最后一个值：");
int secondVal = scnr.nextInt();
for (int i = firstVal; i >= secondVal; i--) {
System.out.println(i+ " ");
}
for (int i = firstVal; i <= secondVal; i++) {
System.out.println(i+ " ");
}
}
}
英文:
I am trying to output "Invalid value" if the MAX_VALUE I have is not an integer. Whenever I run this code, my overall output gets changed. I am wondering how to correctly do this.
import java.util.*;
public class ForLoopPractice {
public static void main(String[]args) {
Scanner scnr = new Scanner(System.in);
final int MAX_VALUE;
System.out.println("Print even values");
System.out.print("Max value: ");
MAX_VALUE = scnr.nextInt();
for (int i=0; i < MAX_VALUE; i++) {
if (i % 2 == 0) {
System.out.println(i + " ");
}
}
while (!scnr.hasNextInt()) {
System.out.println("Invalid value");
scnr.next();
}
System.out.println();
System.out.println("Print a range of values");
System.out.print("First Value: ");
int firstVal = scnr.nextInt();
System.out.print("Last Value: ");
int secondVal = scnr.nextInt();
for (int i = firstVal; i >= secondVal; i--) {
System.out.println(i+ " ");
}
for (int i = firstVal; i <= secondVal; i++) {
System.out.println(i+ " ");
}
}
}
答案1
得分: 1
使用Try-Catch块。如果输入不是数字，Scanner.nextInt()会抛出InputMismatchException。
您可以使用一个函数，确保程序在用户选择正确输入之前不会继续执行。
public static int getValidNumber(){
try{
Scanner sc = new Scanner(System.in);
System.out.println("Enter a number: ");
int num;
num = sc.nextInt();
return num;
} catch (InputMismatchException ex){
System.out.println("Invalid Input.");
return getValidNumber();
}
}
英文:
Use a Try-Catch block. Scanner.nextInt() throws InputMismatchException if the input isn't a number.
You can use a function to make sure the program doesn't go forward until the user has selected the proper input.
public static int getValidNumber(){
try{
Scanner sc = new Scanner(System.in);
System.out.println("Enter a number: ");
int num;
num = sc.nextInt();
return num;
} catch (InputMismatchException ex){
System.out.println("Invalid Input.");
return getValidNumber();
}
}
答案2
得分: 0
你可以使用以下代码将 "MAX_VALUE = scnr.nextInt();" 包装起来：
if (scnr.hasNextInt()) {
MAX_VALUE = scnr.nextInt();
}
这会在下一个值可以被解释为整数时返回 true。
英文:
You could wrap "MAX_VALUE = scnr.nextInt();" with:
if (scnr.hasNextInt())
It will return true if the next value can be interpreted as an integer.
答案3
得分: -1
在输入时，您可以使用isDigit()方法进行检查。
如果N是用户输入的一个值，请使用System.out.print(Character.isDigit('N'))进行检查；
该方法将提供布尔值。
英文:
While taking the input, you can check it by a method isDigit().
If N is a input given by user, check it by System.out.print(Character.isDigit('N'));
The method will provide boolean value.
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