Java 通过使用arraylist添加元素创建接口

使用arraylist在集合中添加一组元素时遇到了一个问题。我有一个班的学生有3个变量。还有一个包含添加、删除和获取学生的界面，但在我的测试中，我无法显示不同的结果

String studId = "";
String firstName = "";
String lastName = "";
int number = 0;
int index = 0;
StudentServiceImpl studServImpl = new StudentServiceImpl();
Scanner scan = new Scanner(System.in);
Student student = new Student();
    do {
        System.out.println("1.Add Student:");
        System.out.println("2.Delete Student:");
        System.out.println("3.Display Students:");
        System.out.println("4.Exit");
        System.out.println();
        System.out.print("Select number: ");
        System.out.println();
        number = scan.nextInt();
        if (number == 1) {
            System.out.println("Enter Student No.");
            studId = scan.next();
            student.setStudId(studId);
            System.out.println("Enter First Name:");
            firstName = scan.next();
            student.setFirstName(firstName);
            System.out.println("Enter Last Name:");
            lastName = scan.next();
            student.setLastName(lastName);
            studServImpl.add(student);
        } else if (number == 2) {
            // TODO:
        } else if (number == 3) {
            List<Student> studentList = new ArrayList<Student>();
            studentList = studServImpl.getStudent();
            System.out.println("\nThe size of List: " + studentList.size());
            for (Student studentRec : studentList) {
                System.out.println("Student ID: " + studentRec.getStudId());
                System.out.println("First Name: " + studentRec.getFirstName());
                System.out.println("Last Name: " + studentRec.getFirstName() + "\n");
            }
        } else if (number == 4) {
            System.out.println("Thank you, Good Bye!");
        }
    } while (number != 0);

---

救命

您在循环外部实例化了

student

，并使用菜单项

1

多次添加它

应该在循环内移动实例化…

String studId=“”；
String studId = "";
String firstName ="";
String lastName ="";
int number =0;
int index = 0;
StudentServiceImpl studServImpl = new StudentServiceImpl();
Scanner scan = new Scanner(System.in);

do{

System.out.println("1.Add Student:");
System.out.println("2.Delete Student:");
System.out.println("3.Display Students:");
System.out.println("4.Exit");
System.out.println();
System.out.print("Select number: ");
System.out.println();
number=scan.nextInt();

if(number==1){
    Student student =  new Student();
    System.out.println("Enter Student No.");
    studId = scan.next();
    student.setStudId(studId);

    System.out.println("Enter First Name:");
    firstName = scan.next();
    student.setFirstName(firstName);

    System.out.println("Enter Last Name:");
    lastName = scan.next();
    student.setLastName(lastName);

    studServImpl.add(student);

}


    else if(number ==2){



    }

    else if (number == 3){

    List<Student> studentList = new ArrayList<Student>();

    studentList = studServImpl.getStudent();

    System.out.println("\nThe size of List: "+studentList.size());



    for (Student studentRec : studentList) {
        System.out.println("Student ID: "+ studentRec.getStudId());
        System.out.println("First Name: "+ studentRec.getFirstName());
        System.out.println("Last Name: "+ studentRec.getLastName()+"\n");


    }

    }

    else if(number == 4){

        System.out.println("Thank you, Good Bye!");
    }



    }


    while(number!=0);

}

字符串firstName=“”；
字符串lastName=“”；
整数=0；
int指数=0；
studentserviceinpl studservinpl=新的studentserviceinpl（）；
扫描仪扫描=新扫描仪（System.in）；
做{
System.out.println（“1.Add Student:”）；
System.out.println（“2.Delete Student:”）；
System.out.println（“3.Display Students:”）；
System.out.println（“4.Exit”）；
System.out.println（）；
系统输出打印（“选择编号：”）；
System.out.println（）；
number=scan.nextInt（）；
如果（数字==1）{
学生=新生（）；
System.out.println（“输入学号”）；
studId=scan.next（）；
student.setStudId（studId）；
System.out.println（“输入名字：”）；
firstName=scan.next（）；
student.setFirstName（firstName）；
System.out.println（“输入姓氏：”）；
lastName=scan.next（）；
student.setLastName（lastName）；
studServImpl.add（学生）；
}
else if（数字=2）{
}
else if（数字=3）{
List studentList=new ArrayList（）；
studentList=studservinpl.getStudent（）；
System.out.println（“\n列表大小：”+studentList.size（））；
用于（学生中心：学生名单）{
System.out.println（“学生ID:+studentRec.getStudId（））；
System.out.println（“名字：+studentRec.getFirstName（））；
System.out.println（“姓氏：“+studentRec.getLastName（）+”\n”）；
}
}
else if（数字=4）{
System.out.println（“谢谢你，再见！”）；
}
}
while（number！=0）；
}

---

您的代码可能是这样的，请注意，我所做的唯一更改是将student对象设置为输入块内的局部变量。

能否格式化代码……您的代码是否编译？您正在调用student.setFirstName，但student是一个数组。欢迎使用堆栈溢出！寻求调试帮助的问题（“为什么这段代码不起作用？”）必须包括所需的行为、特定的问题或错误以及在问题本身中重现它所需的最短代码。没有明确问题陈述的问题对其他读者没有用处。请参见：如何创建。使用“编辑”链接改进您的问题-不要通过评论添加更多信息。谢谢你想让我们花时间帮你做作业。因此，请您花5分钟的时间来编写一个正确的、缩进正确的代码，而不是给我们带来这样的麻烦！我没有看到索引的增加。。。

String studId = "";
String firstName ="";
String lastName ="";
int number =0;
int index = 0;
StudentServiceImpl studServImpl = new StudentServiceImpl();
Scanner scan = new Scanner(System.in);

do{

System.out.println("1.Add Student:");
System.out.println("2.Delete Student:");
System.out.println("3.Display Students:");
System.out.println("4.Exit");
System.out.println();
System.out.print("Select number: ");
System.out.println();
number=scan.nextInt();

if(number==1){
    Student student =  new Student();
    System.out.println("Enter Student No.");
    studId = scan.next();
    student.setStudId(studId);

    System.out.println("Enter First Name:");
    firstName = scan.next();
    student.setFirstName(firstName);

    System.out.println("Enter Last Name:");
    lastName = scan.next();
    student.setLastName(lastName);

    studServImpl.add(student);

}


    else if(number ==2){



    }

    else if (number == 3){

    List<Student> studentList = new ArrayList<Student>();

    studentList = studServImpl.getStudent();

    System.out.println("\nThe size of List: "+studentList.size());



    for (Student studentRec : studentList) {
        System.out.println("Student ID: "+ studentRec.getStudId());
        System.out.println("First Name: "+ studentRec.getFirstName());
        System.out.println("Last Name: "+ studentRec.getLastName()+"\n");


    }

    }

    else if(number == 4){

        System.out.println("Thank you, Good Bye!");
    }



    }


    while(number!=0);

}