[英]Java can't get array list to print out?
所以我有3个类,其中一个可以运行所有代码。 一个学生班,一个研究生班和一个本科班,以及一个运行代码的名为Lab 4的班。 该代码要求有多少个研究生和多少个本科生,然后要求用户输入每个数目的所有信息。 输入所有信息后,本科生或研究生学生对象将添加到学生数组列表中。 添加完所有学生后,然后打印所有信息。 但是,当我输入所有信息时,该数组不打印,程序终止。 我如何获得要打印的阵列?
码:
实验4:创建学生对象,数组列表,将它们添加到数组,并打印添加到数组列表的对象的所有信息
import java.util.ArrayList;
import java.util.Scanner;
public class Lab04 {
public static void main(String[] args) {
ArrayList <Student> studentList = new ArrayList <Student>();
Scanner s = new Scanner(System.in);
System.out.println("How many Graduate Students do you want to store?");
int numOfStudents = s.nextInt();
s.nextLine();
for (int i = 0; i < numOfStudents; i++) {
System.out.println("What is the student's name?");
String name = s.nextLine();
System.out.println("What is the student's GPA?");
double GPA = s.nextDouble();
s.nextLine();
System.out.println("What is the student's ID?");
String ID = s.nextLine();
System.out.println("What is the student's High School?");
String highSchool = s.nextLine();
System.out.println("What is the student's graduate major?");
String gradMajor = s.nextLine();
System.out.println("What is the student's undergraduate major?");
String underMajor = s.nextLine();
System.out.println("What is the student's undergradute school? ");
String underSchool = s.nextLine();
GraduateStudent gradStu = new GraduateStudent(name, GPA, ID, highSchool, gradMajor, underMajor,
underSchool);
studentList.add(gradStu);
}
System.out.println("How many UnderGraduate students are there?");
int numOfUnder = s.nextInt();
s.nextLine();
for (int j = 0; j < numOfUnder; j++) {
System.out.println("What is the student's name?");
String name = s.nextLine();
System.out.println("What is the student's GPA?");
double GPA = s.nextDouble();
s.nextLine();
System.out.println("What is the student's ID?");
String ID = s.nextLine();
System.out.println("What is the student's High School?");
String highSchool = s.nextLine();
System.out.println("What is the student's major?");
String major = s.nextLine();
System.out.println("What the student's minor?");
String minor = s.nextLine();
UnderGraduate UnderGrad = new UnderGraduate(name, GPA, ID, highSchool, major, minor);
studentList.add(UnderGrad);
}
for (int j = 0; j < studentList.size(); j++) {
(studentList.get(j)).getStudentInformation();
}
}
}
学生班:
public class Student {
private String name;
private double gpa;
private String id;
private String highSchool;
//private String major;
//private String minor;
public Student() {
name = "";
gpa = 0.0;
id = "";
highSchool = "";
//major = "";
//minor = "";
}
public Student(String name, double gpa, String id, String highSchool){
this.name = name;
this.gpa = gpa;
this.id = id;
this.highSchool = highSchool;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getGpa() {
return gpa;
}
public void setGpa(double gpa) {
this.gpa = gpa;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getHighSchool() {
return highSchool;
}
public void setHighSchool(String highSchool) {
this.highSchool = highSchool;
}
public String getStudentInformation() {
String result = "Name: " + name + " GPA: " + gpa + " ID: " + id
+ " High School: " + highSchool;
return result;
}
}
研究生班:
public class GraduateStudent extends Student {
private String gradMajor;
private String underMajor;
private String underSchool;
public GraduateStudent(String name, double gpa, String id, String highSchool,
String gradMajor, String underMajor, String underSchool) {
super(name, gpa, id, highSchool);
this.gradMajor = gradMajor;
this.underMajor = underMajor;
this.underSchool = underSchool;
}
public String getGradMajor() {
return gradMajor;
}
public void setGradMajor(String gradMajor) {
this.gradMajor = gradMajor;
}
public String getUnderMajor() {
return underMajor;
}
public void setUnderMajor(String underMajor) {
this.underMajor = underMajor;
}
public String getUnderSchool() {
return underSchool;
}
public void setUnderSchool(String underSchool) {
this.underSchool = underSchool;
}
@Override
public String getStudentInformation() {
String result = super.getStudentInformation()+
"Graduate Major: " + gradMajor + "Undergraduate Major: " + underMajor +
"Undergraduate School: " + underSchool;
return result;
}
}
因为您没有打印任何东西。 更改
for (int j = 0; j < studentList.size(); j++) {
(studentList.get(j)).getStudentInformation();
}
至
for (int j = 0; j < studentList.size(); j++) {
System.out.println((studentList.get(j)).getStudentInformation());
}
当您询问getStudentInformation时,它返回一个String,您现在要对System.out.println(...)
这个String对象进行操作
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