java - 尝试检查输入是否为整数时出现 java.lang.NullPointerException

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 5 年前。

我收到 java.lang.NullPointerException 并且不知道到底是什么原因造成的。我知道这与我的 getInput 方法有关，但我不知道哪一行或多行导致了错误。任何帮助，将不胜感激。

public class Input {

private Scanner scan;

//Checks input is an integer and bigger than 1
public int getInput() {
    String input = scan.next();
    int number = 0;
    boolean isNumber = true;

    while(isNumber) {
        try {
            number = Integer.parseInt(input);
            if(number >= 1) {
                isNumber = false;
            }
        } catch (NumberFormatException e) {
            isNumber = true;
            System.out.println("Error: please enter a whole number that is bigger than 1");
            input = scan.next();
        }
    }

    return number;

}

}

public class Main  {
public static void main (String[] args) {

    Input userInput = new Input();
    System.out.println("\t" +"Collatz Conjecture");
    System.out.println("Please enter a value: ");
    int n;
    n = userInput.getInput();

    System.out.println("Your number is " + n);
   }
}

Answer 1

看起来你没有初始化它，所以它是 null 尝试添加 scan = new Scanner(System.in);您也可以使用 number = scan.nextInt();