java - 我怎样才能在这个循环中合并 'int only' 输入？

Question

我已经对这段代码进行了大约一个小时的研究，现在尝试在用户输入字符而不是数字时使其循环

    System.out.println("Enter level student last completed (0-3): "); 
    int level = in.nextInt();
    while (level > 3 || level < 0){
        System.out.println("Please enter a valid level!: ");
        level = in.nextInt();
    }

我想添加!in.hasNextInt()到线while (level > 3 || level < 0)做到这一点

while (!in.hasNextInt() || level > 3 || level < 0)

但这并没有帮助，因为如果输入字符，程序仍然会崩溃。

编辑:

    System.out.println("Enter level student last completed (0-3): "); 
    int level = 1; //in.nextInt();
    while (in.hasNextInt()==false || level > 3 || level < 0){
        in.next();
        System.out.println("Please enter a valid level!: ");
    }
    level = in.nextInt();

Answer 1

您可以创建一个 while 循环来重复请求输入，直到获得所需的类型

基本解决方案

    int i;
    while(scan.hasNextInt()==false){ //keep asking until it gets something it likes
        scan.next(); //<--consume bad input, important!
        System.out.println("Only integers are valid");
    }
    i=scan.nextInt();
    
    System.out.println(i);

高级解决方案

您可以将其打包到方法中，当我们想要合并更多逻辑时，这将使生活变得更轻松

public static int getSafeInteger(){
    Scanner scan=new Scanner(System.in); //if using scanner over and over consider passing the scanner as an argument
    while(scan.hasNextInt()==false){
        scan.next();
        System.out.println("Only integers are valid");
    }
    return scan.nextInt();
}

然后我们可以在现有循环中使用该方法

    System.out.println("Enter level");
    
    Scanner scan=new Scanner(System.in);
    
    int level=getSafeInteger();
    while (level > 3 || level < 0){
        System.out.println("Please enter a valid level!: ");
        level = getSafeInteger();
    }