第一关

第二关

题目要求：

public static void main(String[] args) {Scanner sc = new Scanner(System.in);try {int num1 = sc.nextInt();int num2 = sc.nextInt();/********* Begin *********/System.out.println(num1/num2);} catch (Exception e) {System.out.println("除数不能为0");}/********* End *********/}

第三关

public static void main(String[] args) throws FileNotFoundException {test();}public static void test()  throws FileNotFoundException           {File file = new File("abc");if(!file.exists()){		//判断文件是否存在//文件不存在，则 抛出 文件不存在异常throw  new FileNotFoundException("该文件不存在");}else{FileInputStream fs = new FileInputStream(file);}}/********* End *********/

第四关

假如有错误，微调一下，可能是行数问题。

public class Task {/********* Begin *********/public  static void main(String[] args) throws MyException{Scanner sc = new Scanner(System.in);String username = sc.next();if (username.length()<3) {//判断用户名throw new MyException("用户名小于三位Exception");}else{System.out.println("用户名格式正确");}}}class  MyException extends Exception{public MyException() {}public MyException(String message) {super(message);}}