线程“main”java中出现异常。util。NoSuchElementException：关闭扫描仪时未找到线条

Question

所以我有3个不同的类，每个都有一个扫描仪。在main方法中，我循环遍历这些类，并为每个类输入几次。问题是当我关闭扫描仪（scanner.close（）；）时，我只能迭代一次，执行的第一个类，然后我得到这个错误：线程“main”中的异常java.util.NoSuchElementException：找不到行。当我不关闭扫描仪时，一切都很好，但我不想有内存泄漏。如果发布代码可以帮助您更好地理解我的问题，请让我知道

代码

''公共类主{

public static void main(String args[]){
    Employee new_guard[] = new Guard[5];
    Employee new_it[] = new ITPersonal[5];
    Employee new_manager[] = new Management[5];
    int count_guard = 0, count_it = 0, count_manager = 0;

    for(int i = 0; i <= 14; i++){
        if(i % 3 == 0){
            new_guard[count_guard] = new Guard();
            new_guard[count_guard].input_variables();
            count_guard++;
            System.out.println();
        }else if(i % 2 == 0){
            new_it[count_it] = new ITPersonal();
            new_it[count_it].input_variables();
            count_it++;
            System.out.println();
        }else{
            new_manager[count_manager] = new Management();
            new_manager[count_manager].input_variables();
            count_manager++;
            System.out.println();
        }
    }

    int k = 0, j = 0, l = 0;

    for(int i = 0; i < 15; i++){
        if(i % 3 == 0){
            System.out.println(new_manager[k].toString());
                k++;
            }else if(i % 2 == 0){
                System.out.println(new_it[j].toString());
                j++;
            }else{
                System.out.println(new_guard[l].toString());
                l++;
            }
        }
    }

}

抽象公共类员工{

public Employee(){}

String name, surname, rang;
int salary = 0, daysoff = 20;

public Employee(String name, String surname, String rank, int salary, int daysoff){
    this.name = name;
    this.surname = surname;
    this.salary = salary;
    this.rank = rank;
    this.daysoff= daysoff;
}

}

导入java.util.扫描仪；

公共类守卫扩展员工{

String rang = "Guard";
int night_shifts, early_shifts, late_shifts;   

public Guard(){}

public void input_variables(){
    Scanner scan = new Scanner(System.in);
    System.out.println("First name: ");
    this.name = scan.nextLine();
    System.out.println("Last name: ");
    this.surname = scan.nextLine();
    System.out.println("Night shifts (per month): ");
    this.night_shifts = scan.nextInt();
    System.out.println("Late shifts (per month): ");
    this.late_shifts = scan.nextInt();
    System.out.println("Night shifts (per month): ");
    this.early_shifts = scan.nextInt();
    // scan.close();
    System.out.printf("Added %s, %s to company!", this.surname, this.name);
}

public int getSalary(){
    return salary = 160 * night_shifts + 100 * (early_shifts + late_shifts);
}

public int getDaysOff(){
    return daysoff += 0.25 * (early_shifts + late_shifts + night_shifts);
}

public String toString(){
    return String.format("%s, %s (%s): Shifts %d/%d/%d; Monthly salary = %d EURO; %d offdays.", 
    surname, name, rank, early_shifts, late_shifts, night_shifts, getSalary(), getDaysOff());
}

}

导入java.util.扫描仪；

公共类ITPersonal扩展员工{

String rang;
int year_joined, weekhours, daysoff = 22;
int current_year = 2021, bonusdays = 0;

public ITPersonal(){}

public void input_variables(){
    Scanner scan = new Scanner(System.in);
    System.out.println("First name: ");
    this.name = scan.nextLine();        
    System.out.println("Last name: ");
    this.surname = scan.nextLine();
    System.out.println("Enter rank (\"Junior Developer" + " or " + "Senior Developer\"): \"");
    this.rank = scan.nextLine();
    System.out.println("Year joined: ");
    this.year_joined = scan.nextInt();
    System.out.println("Week hours: ");
    this.weekhours = scan.nextInt();
    // scan.close();
    System.out.printf("Added %s, %s to company!", this.surname, this.name);
}

public int getDaysOff(){

    if(current_year - year_joined >= 3){
        if((current_year - year_joined) % 3 == 0){
            if((current_year - year_joined) / 3 >= 5){
                bonusDays = 5;
            }else
                bonusDays = (current_year - year_joined) / 3;
        }else{
            if((current_year - year_joined) / 3 >= 5){
                bonusDays = 5;
            }else
                bonusDays = (current_year - year_joined) % 3;
        }
    } 

    if(this.rang == "Senior Developer"){
        daysoff += bonusTage;
    }else
        daysoff = 22;

    return daysoff;
}

public int getSalary(){
    if(rang == "Junior Developer"){
        salary = 25 * weekhours;
    }else{
        salary = (32 * weekhours) + current_year - year_joined;
    }

    return salary;
}

public String toString(){
    return String.format("%s, %s (%s): Weekhours = %d; Monthly salary = %d EURO; %d offdays.", 
    this.surname, this.name, this.rank, this.weekhours, getSalary(), getDaysOff());
}

}

“”

Answer 1

扫描仪不是问题所在。初始化扫描仪时，您可能正在执行

Scanner scanner = new Scanner(System.in);

问题是调用扫描器时。close（），扫描仪正在关闭系统。在中，它是进程的单例（从控制台读取的流）。用正则类包装单例（系统中的）并不是隐藏其存在的解决方案。

要解决此问题，您只需初始化扫描仪一次，然后在程序结束时将其关闭（仅一次）。然后通过依赖项注入给类Scanner的引用。

这方面的一个很好的实现是使用try with resource：

public class Main {
    public static void main(String[] args) {
        try (Scanner scanner = new Scanner(System.in)) {
            // the rest of your program
        } // scanner is automatically closed after the try block.
    }
}