控制一个整数值 null

Question

我在学生课堂上使用扫描仪获得了一些价值：垫子、姓名和姓氏。我想在 mat 的插入是 == "" 而不是代码时完成程序。 例如，当我插入 mat: 8293 时，程序继续运行，但是当我插入 "" 一个空白值时，程序将完成。我认为 mat 值应该转换为 Integer 但不适用于 if 块。

public static void inserimento() {
    Studente s=null;
    do{
        System.out.println("\nmatricola:");
        Scanner mat = new Scanner(System.in);
        int matricola = mat.nextInt();
        Integer i = Integer.valueOf(matricola);
        if(i.equals(null)){
          break;
        }       
      
        System.out.println("\ncognome:");
        Scanner cog = new Scanner(System.in);
        String cognome = cog.next();
      
        System.out.println("\nnome:");
        Scanner nom = new Scanner(System.in);
        String nome = nom.next();
        s = new Studente(matricola,cognome,nome);
    } while(true);
  
    System.out.println("fine inserimento");
}

Answer 1

您可以像字符串一样读取输入并将其解析为整数。这允许您检查输入值是否为空。

 public static void inserimento() {

    Studente s=null;
    do{
        System.out.println("\nmatricola:");
        Scanner mat = new Scanner(System.in);
        
        try {
            String matricola = mat.nextLine();
            if(matricola.equals("")){
                break;
            }   
            Integer i = Integer.valueOf(matricola);
            System.out.println("\ncognome:");
            Scanner cog = new Scanner(System.in);
            String cognome = cog.next();
            System.out.println("\nnome:");
            Scanner nom = new Scanner(System.in);
            String nome = nom.next();
            s = new Studente(matricola,cognome,nome);
        }
        catch(Exception e) {
            System.out.println("the input value must be an Integer");
        }
       
    } while(true);
    System.out.println("fine inserimento");
}

Answer 2

public static void inserimento() {
Studente s=null;
do{
    System.out.println("\nmatricola:");
    Scanner mat = new Scanner(System.in);
    String matricolaString = mat.nextLine();
    if(!matricolaString.equals(""))
    {
        int i  = Integer.parseInt(matricolaString);
    }
    else{
        break;
    }

    System.out.println("\ncognome:");
    Scanner cog = new Scanner(System.in);
    String cognome = cog.next();
  
    System.out.println("\nnome:");
    Scanner nom = new Scanner(System.in);
    String nome = nom.next();
    s = new Studente(matricola,cognome,nome);
} while(true);

System.out.println("fine inserimento");

}