我的问题是使用其他方法显示数据。我尝试了两种方法，但没有输出。
我认为当我把它们作为两个方法的参数时，ArrayList中的对象都消失了。或者不是。
请帮助我解决我的这个问题。还有更多的选择需要填补，我也需要一些帮助。
public class Student {
private String IDNumber;
private String firstName;
private String middleName;
private String lastName;
private String degree;
private int yearLevel;
public Student() {
this.IDNumber = IDNum;
this.firstName = fName;
this.middleName = mName;
this.lastName = lName;
this.degree = deg;
this.yearLevel = level;
}
public void setIdNumber(String IDNumber) {
this.IDNumber = IDNumber;
}
public String getIdNumber() {
return IDNumber;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getFirstName() {
return firstName;
}
public void setMiddleName(String middleName) {
this.middleName = middleName;
}
public String getMiddleName()
{
return middleName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getLastName() {
return lastName;
}
public void setDegree(String degree) {
this.degree = degree;
}
public String getDegree() {
return degree;
}
public void setYearLevel(int yearLevel) {
this.yearLevel = yearLevel;
}
public int getYearLevel() {
return yearLevel;
}
/* @Override
public String toString(){
return ("ID Number: "+this.getIdNumber()+
"\nName: "+ this.getFirstName()+
" "+ this.getMiddleName()+
" "+ this.getLastName()+
"\nDegree and YearLevel: "+ this.getDegree() +
" - " + this.getYearLevel());
} */
}
import java.util.ArrayList;
import java.util.Scanner;
public class test {
public static void main(String[] args) {
menu();
}
public static void menu() {
Scanner in = new Scanner(System.in);
int choice = 0;
System.out.print("****STUDENT RECORD SYSTEM****\n\n");
System.out.println("\t MENU ");
System.out.println("[1]ADD STUDENT");
System.out.println("[2]DISPLAY ALL");
System.out.println("[3]DISPLAY SPECIFIC");
System.out.println("[4]UPDATE");
System.out.println("[5]AVERAGE");
System.out.println("[6]EXIT");
System.out.println("?");
choice = in.nextInt();
if (choice == 1) {
options();
}
else if (choice == 2) {
displayAll(student, studentList);
}
else if (choice == 3) {
displaySpecific(student, studentList);
}
}
public static void options() {
Scanner in = new Scanner(System.in);
ArrayList<Student> studentList = new ArrayList<Student>();
char ans;
String temp;
int total;
do {
System.out.println("TOTAL: ");
total = in.nextInt();
Student[] student = new Student[total];
for (int index = 0; index < student.length; index++) {
student[index] = new Student();
System.out.print("*********STUDENT INFORMATION*********\n\n");
System.out.println("PRESS ENTER");
in.nextLine();
System.out.print("ID NUMBER: ");
student[index].setIdNumber(in.nextLine());
System.out.print("FIRST NAME: ");
student[index].setFirstName(in.nextLine());
System.out.print("MIDDLE NAME: ");
student[index].setMiddleName(in.nextLine());
System.out.print("LAST NAME: ");
student[index].setLastName(in.nextLine());
System.out.print("DEGREE: ");
student[index].setDegree(in.nextLine());
System.out.print("YEAR LEVEL: ");
student[index].setYearLevel(in.nextInt());
studentList.add(student[index]);
}
System.out
.print("Would you like to enter in a new student (y/n)? ");
String answer = in.next();
ans = answer.charAt(0);
} while (ans == 'y');
// SEARCH and DISPLAY SPECIFIC
String id = new String();
in.nextLine();
System.out.print("Enter ID NUMBER: ");
id = in.nextLine();
for (int j = 0; j < studentList.size(); j++) {
if (id.equals(studentList.get(j).getIdNumber())) {
System.out.printf("STUDENT SEARCHED");
System.out.print("\nID NUMBER: "
+ studentList.get(j).getIdNumber());
System.out.print("\nFULL NAME: "
+ studentList.get(j).getFirstName() + " "
+ studentList.get(j).getMiddleName() + " "
+ studentList.get(j).getLastName());
System.out.print("\nDEGREE and YEAR: "
+ studentList.get(j).getDegree() + "-"
+ studentList.get(j).getYearLevel() + "\n\n");
System.out.println();
}
}
// DISPLAY ALL
for (int i = 0; i < studentList.size(); i++) {
System.out.printf("STUDENT[%d]", i + 1);
System.out
.print("\nID NUMBER: " + studentList.get(i).getIdNumber());
System.out.print("\nFULL NAME: "
+ studentList.get(i).getFirstName() + " "
+ studentList.get(i).getMiddleName() + " "
+ studentList.get(i).getLastName());
System.out.print("\nDEGREE and YEAR: "
+ studentList.get(i).getDegree() + "-"
+ studentList.get(i).getYearLevel());
System.out.println();
}
menu();
}
public static void displayAll(Student student,
ArrayList<Student> studentList) {
System.out.printf("STUDENT RECORD");
for (int i = 0; i < studentList.size(); i++) {
System.out.printf("STUDENT[%d]", i + 1);
System.out
.print("\nID NUMBER: " + studentList.get(i).getIdNumber());
System.out.print("\nFULL NAME: "
+ studentList.get(i).getFirstName() + " "
+ studentList.get(i).getMiddleName() + " "
+ studentList.get(i).getLastName());
System.out.print("\nDEGREE and YEAR: "
+ studentList.get(i).getDegree() + "-"
+ studentList.get(i).getYearLevel());
System.out.println();
}
}
public static void displaySpecific(Student student,
ArrayList<Student> studentList) {
String id = new String();
in.nextLine();
System.out.print("Enter ID NUMBER: ");
id = in.nextLine();
for (int j = 0; j < studentList.size(); j++) {
if (id.equals(studentList.get(j).getIdNumber())) {
System.out.printf("STUDENT SEARCHED");
System.out.print("\nID NUMBER: "
+ studentList.get(j).getIdNumber());
System.out.print("\nFULL NAME: "
+ studentList.get(j).getFirstName() + " "
+ studentList.get(j).getMiddleName() + " "
+ studentList.get(j).getLastName());
System.out.print("\nDEGREE and YEAR: "
+ studentList.get(j).getDegree() + "-"
+ studentList.get(j).getYearLevel() + "\n\n");
System.out.println();
}
}
}
}
答案 0 :(得分：2)
移动
ArrayList <Student> studentList = new ArrayList <Student>();
从options方法到类字段。
编辑：
如您所见，现在studentList不是
的局部变量public static void options()
但是班级。
无论如何，我编辑了一些方法的args，因为你不需要将学生作为参数传递，因为现在它是该类的一个字段。
import java.util.ArrayList;
import java.util.Scanner;
public class test {
static ArrayList<Student> studentList = new ArrayList<Student>();
public static void main(String[] args) {
menu();
}
public static void menu() {
Scanner in = new Scanner(System.in);
int choice = 0;
System.out.print("****STUDENT RECORD SYSTEM****\n\n");
System.out.println("\t MENU ");
System.out.println("[1]ADD STUDENT");
System.out.println("[2]DISPLAY ALL");
System.out.println("[3]DISPLAY SPECIFIC");
System.out.println("[4]UPDATE");
System.out.println("[5]AVERAGE");
System.out.println("[6]EXIT");
System.out.println("?");
choice = in.nextInt();
if (choice == 1) {
options();
}
else if (choice == 2) {
displayAll();
}
else if (choice == 3) {
displaySpecific(student);// here you should ask to the user what studend he want to show - here it continues to give you error
}
}
public static void options() {
Scanner in = new Scanner(System.in);
char ans;
String temp;
int total;
do {
System.out.println("TOTAL: ");
total = in.nextInt();
Student[] student = new Student[total];
for (int index = 0; index < student.length; index++) {
student[index] = new Student();
System.out.print("*********STUDENT INFORMATION*********\n\n");
System.out.println("PRESS ENTER");
in.nextLine();
System.out.print("ID NUMBER: ");
student[index].setIdNumber(in.nextLine());
System.out.print("FIRST NAME: ");
student[index].setFirstName(in.nextLine());
System.out.print("MIDDLE NAME: ");
student[index].setMiddleName(in.nextLine());
System.out.print("LAST NAME: ");
student[index].setLastName(in.nextLine());
System.out.print("DEGREE: ");
student[index].setDegree(in.nextLine());
System.out.print("YEAR LEVEL: ");
student[index].setYearLevel(in.nextInt());
studentList.add(student[index]);
}
System.out
.print("Would you like to enter in a new student (y/n)? ");
String answer = in.next();
ans = answer.charAt(0);
} while (ans == 'y');
// SEARCH and DISPLAY SPECIFIC
String id = new String();
in.nextLine();
System.out.print("Enter ID NUMBER: ");
id = in.nextLine();
for (int j = 0; j < studentList.size(); j++) {
if (id.equals(studentList.get(j).getIdNumber())) {
System.out.printf("STUDENT SEARCHED");
System.out.print("\nID NUMBER: "
+ studentList.get(j).getIdNumber());
System.out.print("\nFULL NAME: "
+ studentList.get(j).getFirstName() + " "
+ studentList.get(j).getMiddleName() + " "
+ studentList.get(j).getLastName());
System.out.print("\nDEGREE and YEAR: "
+ studentList.get(j).getDegree() + "-"
+ studentList.get(j).getYearLevel() + "\n\n");
System.out.println();
}
}
// DISPLAY ALL
for (int i = 0; i < studentList.size(); i++) {
System.out.printf("STUDENT[%d]", i + 1);
System.out
.print("\nID NUMBER: " + studentList.get(i).getIdNumber());
System.out.print("\nFULL NAME: "
+ studentList.get(i).getFirstName() + " "
+ studentList.get(i).getMiddleName() + " "
+ studentList.get(i).getLastName());
System.out.print("\nDEGREE and YEAR: "
+ studentList.get(i).getDegree() + "-"
+ studentList.get(i).getYearLevel());
System.out.println();
}
menu();
}
public static void displayAll() {
for (int i = 0; i < studentList.size(); i++) {
System.out.printf("STUDENT[%d]", i + 1);
System.out
.print("\nID NUMBER: " + studentList.get(i).getIdNumber());
System.out.print("\nFULL NAME: "
+ studentList.get(i).getFirstName() + " "
+ studentList.get(i).getMiddleName() + " "
+ studentList.get(i).getLastName());
System.out.print("\nDEGREE and YEAR: "
+ studentList.get(i).getDegree() + "-"
+ studentList.get(i).getYearLevel());
System.out.println();
}
}
public static void displaySpecific(Student student) {
String id = new String();
in.nextLine();
System.out.print("Enter ID NUMBER: ");
id = in.nextLine();
for (int j = 0; j < studentList.size(); j++) {
if (id.equals(studentList.get(j).getIdNumber())) {
System.out.printf("STUDENT SEARCHED");
System.out.print("\nID NUMBER: "
+ studentList.get(j).getIdNumber());
System.out.print("\nFULL NAME: "
+ studentList.get(j).getFirstName() + " "
+ studentList.get(j).getMiddleName() + " "
+ studentList.get(j).getLastName());
System.out.print("\nDEGREE and YEAR: "
+ studentList.get(j).getDegree() + "-"
+ studentList.get(j).getYearLevel() + "\n\n");
System.out.println();
}
}
}
}