java - 在 Main 中引用 ArrayList

Question

我在执行引用 Main 中的 ArrayList 的 System.out.print() 时遇到问题。我的代码...

import java.util.*;

public class Roster {

    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@gmailcom", 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","Jack","Black","jblack14@wgu.edu", 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());}
        }
    }

    public static void print_all(){
        System.out.println("");
        for (Student s: StudentArray) {
            System.out.printf("%s\n",s);
        }
    }
    //Print All Student Info
}

学生类(class)

public 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 E-Mail: %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);
    }
}

我知道这对于某些(或大多数)人来说可能是一项简单的任务，但过去几天我一直在努力解决这个问题。如果我将“print_all”移动到 Main (如“Example”)方法中，它就可以正常工作。但该练习需要一个引用 Main 的新方法。如果您能提供帮助，我将不胜感激。我大学的 Material 对这一点的解释很糟糕。谢谢。

Answer 1

也许你想做这样的事情:

import java.util.ArrayList;
public class Roster {
    ArrayList<Student> studentArray;

    public Roster(ArrayList<Student> ar)
    {
        studentArray=ar;
    }

    public void print_all(){
        System.out.println("");{
        for (Student s: studentArray) {
            System.out.printf("%s\n",s);}}
        //Print All Student Info
    }

    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@gmailcom", 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","Jack","Black","jblack14@wgu.edu", 65, 99, 98, 97));
        //Example of printing specific student data using getters.

        Roster r=new Roster(studentArray);
        r.print_all();
    }

}

正如您所看到的，方法 print_all 现在是类 Roster 的一个方法，您可以在构造函数中传递在 main 中初始化的数组的引用。