Develop Reference

Saving an undefined number of user input

I have created a program in JAVA that has menu Options, 1 to 5. Option 4 being "Add student". Where it asks a 4 questions
Questions:
Please Enter student name:
Please Enter student course:
Please Enter student number:
Please Enter student gender:
After user has given these details, It will save into an array and ends the program. I am quite lost on how to save these details into an array.
This is my program where i tried to find a solution myself, But im relatively new to arrays and method myself.
public static void newstudent (String[] name,String[] course,int[] number,String[] gender)
{
}
public static void selection (int option) // Menu
{
switch (option)
{
case 1:
System.out.println("Display Student option");
break;
case 2:
System.out.println("Search Student");
break;
case 3:
System.out.println("Delete Student");
break;
case 4:
//code for adding new student
break;
case 5:
System.out.println("Exited");
break;
default:JOptionPane.showMessageDialog(null, "Invalid option! Please enter in the range from 1 to 5.", "Error", JOptionPane.ERROR_MESSAGE);
}
}
public static void main(String[] args) {
//Start of Menu loop Statement
int option1 ;
do{
String option = JOptionPane.showInputDialog(null,"Enter your option:\n"+"\n"+"1. Display Students\n"+"2. Search Students\n" + "3. Delete Students\n"+"4. Add Students\n"+"5. Exit ","DMIT Students",JOptionPane.QUESTION_MESSAGE);
option1 = Integer.parseInt(option);
selection(option1);
}while(option1 <1 || option1 > 5);
// End of Menu Loop statement
}
}
i tried doing a for loop to add +1 to these array everytime a user inputs all these details but the for loop will be stuck in a infinite loop. Is there any suggestions that i can get? or easier solutions?

You shouldn't use arrays (the way you are using here) in the first place because you don't want to store the details of single student in four different places i.e. arrays. You can define a class Student with all the details you need and then it will be simple to add the details using class instances. Something like -
public class Student
{
private String m_name;
private int m_age;
private String m_course;
private String m_year;
private String m_section;
public Student( String name, int age, String course, String year, String section )
{
m_name = name;
m_age = age;
m_course = course;
m_year = year;
m_section = section;
}
public String getName()
{
return m_name;
}
public int getAge()
{
return m_age;
}
public String getCourse()
{
return m_course;
}
public String getYear()
{
return m_year;
}
public String getSection()
{
return m_section;
}
public String toString()
{
return "name: " + m_name + ", age: " + m_age +
", course: " + m_course + ", year: " + m_year +
", section: " + m_section;
}
public static void main(String[] args)
{
ArrayList<Student> students = new ArrayList<Student>();
Scanner input = new Scanner(System.in);
int menuChoice = 4;
do {
System.out.println("\t\t\tStudent Record Menu");
System.out.println("\t\t1. Add Student\t2. View Students\t3. Search Student\t4. Exit");
try {
System.out.println("Enter a choice: ");
menuChoice = Integer.parseInt(input.nextLine());
} catch (NumberFormatException e) {
continue;
}
if (menuChoice==1)
{
System.out.println("Full name:");
String name = input.nextLine();
int age = -1;
do {
try {
System.out.println("Age:");
age = Integer.parseInt(input.nextLine());
} catch (NumberFormatException e) {
System.out.println("Enter a number!");
continue;
}
} while (age <= 0);
System.out.println("Course:");
String course = input.nextLine();
System.out.println("Year:");
String year = input.nextLine();
System.out.println("Section:");
String section = input.nextLine();
Student student = new Student(name, age, course, year, section);
students.add(student);
} else if (menuChoice==2) {
System.out.println("Students:");
for (Student student : students)
{
System.out.println(student);
}
}
} while (menuChoice<4);
}
}
The above code snippet is referred from here.

Java passing class array into array

I am a student and looking for help with an assignment. Here is the task: Create a CollegeCourse class. The class contains fields for the course ID (for example, “CIS 210”), credit hours (for example, 3), and a letter grade (for example, ‘A’).
Include get() and set()methods for each field. Create a Student class containing an ID number and an array of five CollegeCourse objects. Create a get() and set() method for the Student ID number. Also create a get() method that returns one of the Student’s CollegeCourses; the method takes an integer argument and returns the CollegeCourse in that position (0 through 4). Next, create a set() method that sets the value of one of the Student’s CollegeCourses; the method takes two arguments—a CollegeCourse and an integer representing the CollegeCourse’s position (0 through 4).
I am getting runtime errors on the second for loop where I am trying to get the data into the course array. It is asking for both the CourseID and Hours in the same line and regardless of what I respond with it I am getting an error, it almost seems like it is trying to get all the arrays variables at the same time. Here is my code which includes three classes. Any help to send me in the right direction is appreciated as I have spent a ton of time already researching to resolve.
public class CollegeCourse {
private String courseId;
private int creditHours;
private char grade;
public CollegeCourse(String id, int hours, char grade)
{
courseId=id;
creditHours = hours;
this.grade = grade;
}
public void setCourseId(String id)
{
courseId = id;//Assign course id to local variable
}
public String getCourseId()
{
return courseId;//Provide access to course id
}
public void setHours(int hours)
{
creditHours = hours;//Assign course id to local variable
}
public int getHours()
{
return creditHours;//Provide access to course id
}
public void setGrade(char grade)
{
this.grade = grade;//Assign course id to local variable
}
public char getGrade()
{
return grade;//Provide access to course id
}
}
Student Class
public class Student {
final int NUM_COURSES = 5;
private int studentId;
private CollegeCourse courseAdd;//Declares a course object
private CollegeCourse[] courses = new CollegeCourse[NUM_COURSES];
//constructor using user input
public Student(int studentId)
{
this.studentId=studentId;
}
public void setStudentId(int id)
{
studentId = id;//Assign course id to local variable
}
public int getStudentId()
{
return studentId;//Provide access to course id
}
public void setCourse(int index, CollegeCourse course)
{
courses[index] = course;
}
public CollegeCourse getCourse(int index)
{
return courses[index];
//do I need code to return the courseId hours, grade
}
}
InputGrades Class
import java.util.Scanner;
public class InputGrades {
public static void main(String[] args) {
final int NUM_STUDENTS = 2;
final int NUM_COURSES = 3;
Student[] students = new Student[NUM_STUDENTS];
int s;//subscript to display the students
int c;//subscript to display courses
int stId;
int csIndex;
String courseId = "";
int hours = 0;
//String gradeInput;
char grade = 'z';
CollegeCourse course = new CollegeCourse(courseId,hours, grade);//not sure if I am handling this correctly
Scanner input = new Scanner(System.in);
for(s = 0; s<NUM_STUDENTS; ++s)
{
students[s] = new Student(s);
System.out.print("Enter ID for student #" + (s+1) + ":");
stId = input.nextInt();
input.nextLine();
students[s].setStudentId(stId);
for(c=0; c < NUM_COURSES; ++c)
{
csIndex=c;
System.out.print("Enter course ID #" + (c+1) + ":");
courseId = input.nextLine();
course.setCourseId(courseId);
System.out.print("Enter hours:");
hours = input.nextInt();
input.nextLine();
course.setHours(hours);
String enteredGrade = "";
while(enteredGrade.length()!=1) {
System.out.print("Enter grade:");
enteredGrade = input.nextLine();
if(enteredGrade.length()==1) {
grade = enteredGrade.charAt(0);
} else {
System.out.println("Type only one character!");
}
}
course.setGrade(grade);
students[s].setCourse(csIndex, course);
}
}
for(s = 0; s<NUM_STUDENTS; ++s)
{
System.out.print("\nStudent# " +
students[s].getStudentId());
System.out.println();
for(c=0;c<NUM_COURSES;++c)
System.out.print(students[s].getCourse(c) + " ");
System.out.println();
}
}
}

After input.nextInt() you need to add one more input.nextLine(); and than you can read grade.
System.out.print("Enter hours:");
hours = input.nextInt();
input.nextLine();
course.setHours(hours);
Why it is needed? See this question: Scanner is skipping nextLine() after using next(), nextInt() or other nextFoo() methods
You should add a very simple length validation when you input the grade:
String enteredGrade = "";
while(enteredGrade.length()!=1) {
System.out.print("Enter grade:");
enteredGrade = input.nextLine();
if(enteredGrade.length()==1) {
grade = enteredGrade.charAt(0);
} else {
System.out.println("Type only one character!");
}
}
so the full main class code:
import java.util.Scanner;
/**
* Created by dkis on 2016.10.22..
*/
public class App {
public static void main(String[] args) {
final int NUM_STUDENTS = 10;
final int NUM_COURSES = 5;
Student[] students = new Student[NUM_STUDENTS];
//String name;
int s;//subscript to display the students
int c;//subscript to display courses
int stId;
int csIndex;
String courseId = "";
int hours = 0;
char grade = 'z';
CollegeCourse course = new CollegeCourse(courseId,hours, grade);//not sure if I am handling this correctly
Scanner input = new Scanner(System.in);
for(s = 0; s<NUM_STUDENTS; ++s)
{
students[s] = new Student(s);
System.out.print("Enter ID for student #" + s+1 + ":");
stId = input.nextInt();
input.nextLine();
students[s].setStudentId(stId);
for(c=0; c < NUM_COURSES; ++c)
{
//CollegeCourse course = students[s].getCourse(c);
csIndex=c;
System.out.print("Enter course ID#" + c+1 + ":");
courseId = input.nextLine();
course.setCourseId(courseId);
System.out.print("Enter hours:");
hours = input.nextInt();
input.nextLine();
course.setHours(hours);
String enteredGrade = "";
while(enteredGrade.length()!=1) {
System.out.print("Enter grade:");
enteredGrade = input.nextLine();
if(enteredGrade.length()==1) {
grade = enteredGrade.charAt(0);
} else {
System.out.println("Type only one character!");
}
}
course.setGrade(grade);
students[s].setCourse(csIndex, course);
}
}
for(s = 0; s<NUM_STUDENTS; ++s)
{
System.out.print("\nStudent# " +
students[s].getStudentId());
for(c=0;c<NUM_COURSES;++c)
System.out.print(students[s].getCourse(c) + " ");
System.out.println();
}
}
}

Error when removing student from Java arraylist

I am struggling to get this program to do exactly what the assignment asks. It throws a null pointer exception when trying to remove an added student. Also when I list the students, it shows null on everything.
-Code is fixed-
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
ArrayList<Student> newStudents = new ArrayList<Student>();
System.out.println("Welcome to the Student Interface!.");
System.out.println("Please select a number from the options below \n");
while (true) {
// Give the user a list of their options
System.out.println("1: Add a student to the list.");
System.out.println("2: Remove a student from the list.");
System.out.println("3: Display all students in the list.");
System.out.println("0: Exit the student interface.");
// Get the user input
int userChoice = input.nextInt();
switch (userChoice) {
case 1:
addStudents(newStudents);
break;
case 2:
removeStudent(newStudents);
break;
case 3:
displayStudent(newStudents);
break;
case 0:
System.out.println("Thank you for using the student interface. See you again soon!");
System.exit(0);
}
}
}
public static void addStudents(ArrayList<Student> newStudents) {
Scanner input = new Scanner(System.in);
Student newStudent = new Student();
System.out.println("Please enter first name: ");
String First_Name = input.next();
newStudent.setFirst_Name(First_Name);
System.out.println("Please enter last name: ");
String Last_Name = input.next();
newStudent.setLast_Name(Last_Name);
System.out.println("Please enter major: ");
String Major = input.next();
newStudent.setMajor(Major);
System.out.println("Please enter GPA: ");
String GPA = input.next();
newStudent.setGPA(GPA);
System.out.println("Please enter UIN: ");
String UIN = input.next();
newStudent.setUIN(UIN);
System.out.println("Please enter NetID: ");
String NetID = input.next();
newStudent.setNetID(NetID);
System.out.println("Please enter Age: ");
String Age = input.next();
newStudent.setAge(Age);
System.out.println("Please enter Gender: ");
String Gender = input.next();
newStudent.setGender(Gender);
if (newStudents.size() <= 10) {
newStudents.add(newStudent);
System.out.println("Student added\n");
} else {
System.out.println("\n Student interface is full!");
}
}
private static void displayStudent(ArrayList<Student> newStudents) {
for (Student e : newStudents) {
System.out.println(e);
}
}
private static void removeStudent(ArrayList<Student> newStudents) {
Scanner input = new Scanner(System.in);
System.out.println("Please, enter the UIN to remove the Student: ");
String uin = input.nextLine();
for (Student e : newStudents) {
if (e.getUIN().equals(uin)) {
newStudents.remove(e);
System.out.println("Student removed");
break;
}
else {
System.out.println("Sorry, no such student with this " + uin + " " + "number exist");
}
}
}
Student Class:
package assignments;
public class Student{
private String First_Name;
private String Last_Name;
private String Major;
private String GPA;
private String UIN;
private String NetID;
private String Age;
private String Gender;
public String getFirstName()
{
return First_Name;
}
public void setFirst_Name(String value)
{
this.First_Name = value;
}
public String getLastName()
{
return Last_Name;
}
public void setLast_Name(String value)
{
Last_Name = value;
}
public String getMajor()
{
return Major;
}
public void setMajor(String value)
{
Major = value;
}
public String getGPA()
{
return GPA;
}
public void setGPA(String value)
{
GPA = value;
}
public String getUIN()
{
return UIN;
}
public void setUIN(String value)
{
UIN = value;
}
public String getNetID()
{
return NetID;
}
public void setNetID(String value)
{
NetID = value;
}
public String getAge()
{
return Age;
}
public void setAge(String value)
{
Age = value;
}
public String getGender()
{
return Gender;
}
public void setGender(String value)
{
Gender = value;
}
public String toString()
{
return "First Name: " + First_Name +
"\n Last Name: " + Last_Name +
"\n Major: " + Major +
"\n GPA: " +GPA+
"\n UIN: " + UIN +
"\n NetID: " + NetID+
"\n Age: " + Age+
"\n Gender: " + Gender;
}
public void createStudent(String first_Name2, String last_Name2, String major2, String gPA2, String uIN2, String netID2,
String age2, String gender2) {
first_Name2 = First_Name;
last_Name2 = Last_Name;
major2 = Major;
gPA2 = GPA;
uIN2 = UIN;
age2 = Age;
gender2 = Gender;
}
}

Your program runs about perfectly on my computer. Here’s an example run:
Welcome to the Student Interface!.
Please select a number from the options below
1: Add a student to the list.
2: Remove a student from the list.
3: Display all students in the list.
0: Exit the student interface.
2
Please, enter the UIN to remove the Student:
13
1: Add a student to the list.
2: Remove a student from the list.
3: Display all students in the list.
0: Exit the student interface.
1
Please enter first name:
o
Please enter last name:
v
Please enter major:
cs
Please enter GPA:
g
Please enter UIN:
79
Please enter NetID:
o
Please enter Age:
57
Please enter Gender:
m
Student added
1: Add a student to the list.
2: Remove a student from the list.
3: Display all students in the list.
0: Exit the student interface.
3
Student [firstName=o, lastName=v, major=cs, gPA=g, uIN=79, netID=o, age=57, gender=m]
1: Add a student to the list.
2: Remove a student from the list.
3: Display all students in the list.
0: Exit the student interface.
2
Please, enter the UIN to remove the Student:
79
Student removed
1: Add a student to the list.
2: Remove a student from the list.
3: Display all students in the list.
0: Exit the student interface.
3
1: Add a student to the list.
2: Remove a student from the list.
3: Display all students in the list.
0: Exit the student interface.
0
Thank you for using the student interface. See you again soon!
Potential issues in your program include: You have two Scanner objects on System.in, you may want to share just one. You don’t use the variable student_added. In my two cases the program didn’t report back to the user whether a student was removed or not. Your two TODO comments are obsolete and should be removed.

One of two reasons you'd get a NullPointerException on the remove operation. Either the ArrayList is null, or the object you are attempting to remove is null. Check for those.

I have some issue with my output

The Cullerton Part District holds a mini-Olympics each summer. Create a class named Participant with fields for a name, age, and street address. Include a constructor that assigns parameter values to each field and a toString() method that returns a String containing all the values. Also include an equals() method that determines two Participants are equal if they have the same values in all three fields. Create an application with two arrays of at least 5 Participants each--one holds the Participants in the mini-marathon and the other holds Participants in the diving competition. Prompt the user for Participants who are in both events save the files as BC.java and ABC.java.
import javax.swing.JOptionPane;
import java.util.*;
public class ABC {
private static Participant mini[] = new Participant[2];
public static void main(String[] args) {
setParticipant();
displayDetail();
}
// BC p=new BC(name,age,add);
//displayDetails();
// System.out.println( p.toString());
public static void displayDetail() {
String name=null;
String add = null;
int age=0;
System.out.println("Name\tAdress\tAge");
BC p=new BC(name,age,add);
for (int x = 0; x < mini.length; x++) {
//Participant p1=mini[x];
System.out.println(p.toString());
}
}
public static String getName() {
Scanner sc = new Scanner(System.in);
String name;
System.out.print(" Participant name: ");
return name = sc.next();
}
// System.out.print(" Participant name: ");
// name = sc.next();
public static int getAge() {
int age;
System.out.print(" Enter age ");
Scanner sc=new Scanner(System.in);;
return age= sc.nextInt();
}
public static String getAdd() {
String add;
Scanner sc=new Scanner(System.in);;
System.out.print("Enter Address: ");
return add=sc.next();
}
public static void setParticipant(){
for (int x = 0; x < mini.length; x++) {
System.out.println("Enter loan details for customer " + (x + 1) + "...");
//Character loanType=getLoanType();
//String loanType=getLoanType();
String name=getName();
String add=getAdd();
int age=getAge();
System.out.println();
}
}
}
//another class
public class BC {
private String name;
private int age;
private String address;
public BC(String strName, int intAge, String strAddress) {
name = strName;
age = intAge;
address = strAddress;
}
#Override
public String toString() {
return "Participant [name=" + name + ", age=" + age + ", address=" + address + "]";
}
public boolean equals(Participant value){
boolean result;
if (name.equals(name) && age==value.age && address.equals(address))
result=true;
else
result=false;
return result;
}
}
outPut:
Enter loan details for customer 1...
Participant name: hddgg
Enter Address: 122
Enter age 12
Enter loan details for customer 2...
Participant name: ddjkjde
Enter Address: hdhhd23
Enter age 12
//Why I'm not getting right output
Name Adress Age
Participant [name=null, age=0, address=null]
Participant [name=null, age=0, address=null]

You are getting that output because of this method:
public static void displayDetail() {
String name=null;
String add = null;
int age=0;
System.out.println("Name\tAdress\tAge");
BC p=new BC(name,age,add);
for (int x = 0; x < mini.length; x++) {
//Participant p1=mini[x];
System.out.println(p.toString());
}
}
You are creating a BC with null for name and add and 0 for age. You are then printing it twice.

Populating an array Using Polymorphism

Here is my code. I did my work a bit off. I was supposed to not just do one applicant, I was supposed to do many and I was supposed to populate the applicants into 2 different arrays, one for graduates, and one for undergraduates. I need help figuring out how to make an empty array and fill up applicants in those. A start would help
import java.util.Scanner;
public class CollegeApplicant
{
String applicantName;
String collegeName;
public String getApplicantName()
{
return applicantName;
}
public void setApplicantName(String applicantName)
{
this.applicantName = applicantName;
}
public String getCollegeName()
{
return collegeName;
}
public void setCollegeName(String collegeName)
{
this.collegeName = collegeName;
}
public void checkCollege()
{
int choice;
Graduate g = new Graduate();
Undergraduate ug = new Undergraduate();
Scanner input = new Scanner(System.in);
System.out.println("1. Undergraduate");
System.out.println("2. Graduate");
System.out.println("enter your choice ");
choice = input.nextInt();
if (choice == 1)
{
System.out.println("Enter SAT marks :");
ug.SAT = input.nextDouble();
System.out.println("Enter GPA marks :");
ug.GPA = input.nextDouble();
}
else
{
System.out.println("Enter the origin of college:");
g.collegeOrigin = input.next();
System.out.println("Status :" + g.checkCollege());
}
}
public class Undergraduate
{
double SAT;
double GPA;
}
public class Graduate
{
String collegeOrigin;
String checkCollege()
{
String information = null;
if (collegeName.equals(collegeName)) information = "Applicant is applying from inside";
else information = "Applicant is applying from outside";
return information;
}
}
}
The Client
import java.util.Scanner;
public class CollegeApplicantClient extends CollegeApplicant
{
public static void main(String[] args)
{
TestCollege tc = new TestCollege();
Scanner input = new Scanner(System.in);
System.out.println("Enter the name of applicant ");
tc.setApplicantName(input.next());
System.out.println("enter the college name of applicant ");
tc.setCollegeName(input.next());
tc.checkCollege();
}
}
Here is an example of the possible output
Name: Joe
College Applied to: Harvard
SAT: 5
GPA: 2
Name: Tom
College Applied to: Yale
College of Origin: NYU – from outside
I need to be able to put the graduates in an array and the undergrads in an array. Then display it when it's all done