Question

我看过这里有类似问题的答案，但我无法将它们与我的代码相符。我的代码：

Student Class / StudentArrayList Class

import java.util.*;

class Student {

    private String StuID;
    private String FName;
    private String LName;
    private String Email;
    private int Age;
    private double Grade1;
    private double Grade2;
    private double Grade3;

    public Student (String stuid, String fname, String lname, String email,
        int age, double grade1, double grade2, double grade3)
    {
        this.StuID = stuid;
        this.FName = fname;
        this.LName = lname;
        this.Email = email;
        this.Age = age;
        this.Grade1 = grade1;
        this.Grade2 = grade2;
        this.Grade3 = grade3;
    }

    public String getStuID(){ return this.StuID;}

    public String getFName(){return this.FName;}

    public String getLName(){return this.LName;}

    public String getEmail(){return this.Email;}

    public int getAge(){return this.Age;}

    public double getGrade1(){return this.Grade1;}

    public double getGrade2(){return this.Grade2;}

    public double getGrade3(){return this.Grade3;}

    public String setStuID(String newStuID){return (this.StuID= newStuID);}

    public String setFName(String newFName){return (this.FName= newFName);}

    public String setLName(String newLName){return (this.LName= newLName);}

    public String setEmail(String newEmail){return (this.Email= newEmail);}

    public int setAge(int newAge){return (this.Age= newAge);}

    public double setGrade1(double newGrade1){return (this.Grade1= newGrade1);}

    public double setGrade2(double newGrade2){return (this.Grade2= newGrade2);}

    public double setGrade3(double newGrade3){return (this.Grade1= newGrade3);}

    public String toString() {
        return String.format("StuID: %s\t First Name: %s\t Last Name: %s\t EMail: %s\t Age: %s\t Grade1: %s\t Grade2: %s\t Grade3: %s\t", 
            this.StuID, this.FName, this.LName, this.Email,
            this.Age, this.Grade1, this.Grade2, this.Grade3);

    }
}

public class StudentArrayList {

    public static void main(String[]args){

        ArrayList<Student> StudentArray = new ArrayList<Student>();

        StudentArray.add(new Student("1","John","Smith","John1989@gmail.com", 20, 88, 79, 59));
        StudentArray.add(new Student("2","Susan","Erickson","Erickson_1990@gmail.com", 19, 91, 72, 85));
        StudentArray.add(new Student("3","Jack","Napoli","The_lawyer99yahoo.com", 19, 85, 84, 87));
        StudentArray.add(new Student("4","Erin","Black","Erin.black@comcast.net", 22, 91, 98, 82));
        StudentArray.add(new Student("5","Tom","Gaye","tgay@att.net", 65, 99, 98, 97));

        //Example of printing specific student data using getters.
        System.out.println("");
        for (Student a: StudentArray) {
            System.out.println(a.getStuID());
            System.out.println(a.getFName());
            System.out.println(a.getLName());

        }
    }
}

名册等级

public class Roster {
    public static void main(String[]args){
        System.out.println("");
        for (Student s: StudentArray) { //THIS IS WHERE IT ERRORS
            System.out.printf("%s\n",s);
        }
    }
}

我遇到的问题是我正在尝试在System.out.print课程中执行Roster。我得到的错误是Roster类中的“StudentArray无法解析为变量”。如果我在main中的StudentArrayList方法下执行此操作，则print方法可以正常工作。我知道我必须有办法调用阵列，只是不确定该怎么做。这会是一个吸气剂吗？

Answer 1

＆＃34; StudentArray无法解析为变量＆＃34;

这意味着您尚未声明变量StudentArray。

public class Roster {

    public static void main(String[]args){
        ArrayList<Student> StudentArray = new ArrayList<Student>();

        for (Student s: StudentArray) { // loop through the array
            System.out.printf("%s\n",s);
        }
    }
}

Answer 2

您需要先声明studentArray

ArrayList<Student> studentArray = new ArrayList<Student>();

填充添加一些学生，例如：

Student stud1 = new Student("stud params");
//other students declaration
//you could do this with a loop if data are asked to user
studentArray.add(stud1);

然后打印整个列表：

for(Student s: studentArray){
     System.out.println(%s\n",s);
}

Answer 3

我认为你根本不需要Roster类，因为你想让程序在Student类中完成。你不能有两个带有main的类，Student Class和Roster Class都有Main。

学生班的主要是做正确的事，它正在初始化学生并打印名册。

所以你可以做两件事删除Roster类或取出这段代码

public class StudentArrayList {

public static void main(String[]args){

    ArrayList<Student> StudentArray = new ArrayList<Student>();

    StudentArray.add(new Student("1","John","Smith","John1989@gmail.com", 20, 88, 79, 59));
    StudentArray.add(new Student("2","Susan","Erickson","Erickson_1990@gmail.com", 19, 91, 72, 85));
    StudentArray.add(new Student("3","Jack","Napoli","The_lawyer99yahoo.com", 19, 85, 84, 87));
    StudentArray.add(new Student("4","Erin","Black","Erin.black@comcast.net", 22, 91, 98, 82));
    StudentArray.add(new Student("5","Tom","Gaye","tgay@att.net", 65, 99, 98, 97));

    //Example of printing specific student data using getters.
    System.out.println("");
        for (Student a: StudentArray) {
            System.out.println(a.getStuID());
            System.out.println(a.getFName());
            System.out.println(a.getLName());

        }   

}

到名册，这将完成这项工作。

坚持从另一个类

3 个答案: