Java使用扫描程序时如何验证输入？
此示例显示了使用时如何验证输入java.util.Scanner。为了验证输入，Scanner该类提供了一些hasNextXXX()可用于验证输入的方法。例如，如果我们要检查输入是否为有效整数，可以使用该hasNextInt()方法。
在下面的代码片段中，将演示如何验证用户是否提供正整数。程序将重复执行，直到提供正确的输入为止。
package org.nhooo.example.util;
import java.util.Scanner;
public class ScannerValidateInput {
public static void main(String[] args) {
ScannerValidateInput demo = new ScannerValidateInput();
demo.validatePositiveNumber();
}
private void validatePositiveNumber() {
Scanner scanner = new Scanner(System.in);
int number;
do {
System.out.print("Please enter a positive number: ");
while (!scanner.hasNextInt()) {
String input = scanner.next();
System.out.printf("\"%s\" is not a valid number.\n", input);
}
number = scanner.nextInt();
} while (number < 0);
System.out.printf("You have entered a positive number %d.\n", number);
}
}代码段产生的输出：
Please enter a positive number: qwerty "qwerty" is not a valid number. @@@ "@@@" is not a valid number. -100 Please enter a positive number: 99 You have entered a positive number 99.
另一个示例是验证用户是否正确输入了字母来邀请一个秘密单词。在下面的代码段中，如果用户未输入字母，则该代码将继续要求输入有效的字母。循环直到输入字母的长度等于秘密单词的长度。
private void validateLetter() {
String secretWord = "Hello";
Scanner scanner = new Scanner(System.in);
int length = 0;
StringBuilder guess = new StringBuilder();
do {
System.out.print("Enter a letter to guess: ");
char letter = scanner.next().charAt(0);
if (Character.isLetter(letter)) {
guess.append(letter);
length++;
}
} while (length < secretWord.length());
if (secretWord.equalsIgnoreCase(guess.toString())) {
System.out.println("You are correct!");
} else {
System.out.println("Please try again!");
}
}Enter a letter to guess: 1 Enter a letter to guess: 2 Enter a letter to guess: H Enter a letter to guess: e Enter a letter to guess: l Enter a letter to guess: l Enter a letter to guess: o You are correct!