我的程序不会遇到异常

Question

如果用户输入负数，为什么这个代码不会捕获错误？

public class Lab12 {

    public static void main(String[] args) {

            Course[] course1 = courses();
            print(course1);
    }//end main

    public static Course[] courses() throws IllegalArgumentException{
        Scanner input = new Scanner(System.in);
        System.out.println("How many courses?");
        int numCourses = input.nextInt();
        Course[] array = new Course[numCourses];
        int s = 0;
        boolean b = true;
        for(int i = 0; i<numCourses; i++){
            System.out.println("Enter the course title.");
            String t = input.nextLine();
            t = input.nextLine();
            System.out.println("Enter the corresponding major.");
            String m = input.nextLine();
            do{
                try{
                System.out.println("Enter the number of students taking this course.");
                s = input.nextInt();
                b = false;
            }//end try block
            catch(IllegalArgumentException ex){
                System.out.println("Input error."+
            "\nPlese enter a positive number for students.");}//end catch
            }while(b);
//Right here I dont see why my try catch wont work
            Course c = new Course(t,m,s);
            array[i] = c;
        }//end for loop
        input.close();
        return array;
}//end courses method
    public static void print(Course[] c){
        for(int i = 0; i<c.length; i++){
        System.out.println("Course title: "+c[i].getTitle()+
                "\nMajor: "+c[i].getMajor()+
                "\nNumber of Students: "+c[i].getStudents());
        }//end for loop
    }//end 
}//end lab12

这是与主要相关的类：

public class Course {

    private String title;
    private String major;
    private int students;

    public Course(String t, String m, int s){

        title = t;
        major = m;
        students = s;
        if(students<0){
        throw new IllegalArgumentException("Wrong Argument.");
        }
//my instruction were to throw an exception in the constructor is this correct
    }//end constructor method
    public String getTitle(){
        return title;
    }//end get title
    public String getMajor(){
        return major;
    }//end get major
    public int getStudents(){
        return students;
    }//end get students
    public void setTitle(String t){
        title = t;
    }//end set title
    public void setMajor(String m){
        major = m;
    }//end set major
    public void setStudents(int s){
        students = s;
    }//end set students
}//end Class Course

Answer 1

为了在Java中捕获异常，您需要在try/catch块中包围抛出异常的代码。

将主for循环更改为以下内容：

for(int i = 0; i<numCourses; i++){
        System.out.println("Enter the course title.");
        String t = input.nextLine();
        t = input.nextLine();
        System.out.println("Enter the corresponding major.");
        String m = input.nextLine();

        // Need to declare the Course object outside of the do/while so that it stays 
        // in scope afterwards
        Course c = null;

        do{
            try{
                System.out.println("Enter the number of students taking this course.");
                s = input.nextInt();
                b = false;

                // Create the Course here so that the try/catch will correctly catch
                // the IllegalArgumentException
                c = new Course(t,m,s);

            }//end try block
            catch(IllegalArgumentException ex){
                System.out.println("Input error."+
                "\nPlease enter a positive number for students.");
            }//end catch
        } while(b);

        array[i] = c;

    }//end for loop