We Keep Coding

How do you connect a single scanner to two arrays?

Basically, I'm trying to ask the user's input and the input should store in two arrays using a single scanner. Using two would ask the user twice and that would be impractical. The code looks like this
int record = 0;
Scanner midOrFinal = new Scanner(System.in);
Scanner scansubjects = new Scanner(System.in);
Scanner scangrades = new Scanner(System.in);
System.out.println("Press 1 to Record for Midterm");
System.out.println("Press 2 to Record for Final Term");
record = midOrFinal.nextInt();
int midterm[] = new int[8];
int grades[] = new int[8];
{
if ( record == 1 )
System.out.println("Enter 8 subjects and their corresponding grades:");
System.out.println();
int i = 0;
for( i = 0; i < 8; i++ )
{
System.out.println(subjects[i]);
System.out.print("Enter Grade: ");
grades[i] = scangrades.nextInt();
if( i == ( subjects.length) )
System.out.println();
}
System.out.println("Enter Grade Successful");
}
If the user chooses option 1, the user will be given some subjects in an array (which I didn't include) and asked to input the grades. The input shall then proceed to the midterm OR finalterm array but I can't seem to do it by using one scanner.
If there are better ideas than my proposed idea, then please share. I'm still very new in Java and my first time using stackoverflow. Thanks!

Break out the grade collection into a new function, and pass along the array you want to collect the grades into.
public static void main(String[] args) throws IOException {
int gradeType = 0;
// Use a single scanner for all input
Scanner aScanner = new Scanner(System.in);
System.out.println("Press 1 to Record for Midterm");
System.out.println("Press 2 to Record for Final Term");
gradeType = aScanner.nextInt();
String[] subjects = { "Subject A", "Subject B" };
int[] midtermGrades = new int[subjects.length];
int[] finalGrades = new int[subjects.length];
int[] gradesToCollect;
// Use gradesToCollect to reference the array you want to
// collect into.
//
// Alternatively, we could call collectGrades() in both the if/else
// condition
if (gradeType == 1) {
gradesToCollect = midtermGrades;
} else {
gradesToCollect = finalGrades;
}
collectGrades(subjects, gradesToCollect, aScanner);
System.out.println("\n\nThese are the collected grades");
System.out.println("Mid Final");
for (int i = 0; i < subjects.length; i++) {
System.out.format("%3d %3d\n", midtermGrades[i], finalGrades[i]);
}
}
// Collect a grade for each subject into the given grades array.
public static void collectGrades(final String[] subjects, final int[] grades, Scanner scn) {
System.out.format("Enter %s subjects and their corresponding grades:",
subjects.length);
System.out.println();
for (int i = 0; i < subjects.length; i++) {
System.out.format("Enter Grade for %s : ", subjects[i]);
grades[i] = scn.nextInt();
if (i == (subjects.length))
System.out.println();
}
System.out.println("Enter Grade Successful");
}

class Main {
public static final Scanner in = new Scanner(System.in);
public static void main(String[] args) {
in.useDelimiter("\r?\n");
Student student = new Student();
System.out.println("Press 1 to Record for Midterm");
System.out.println("Press 2 to Record for Final Term");
int record = in.nextInt();
if (record == 1) {
student.setTerm(TermType.MID);
System.out.println("Enter 8 subjects and their corresponding grades:");
System.out.println("Enter Subject and grades space separated. Example - \nMaths 79");
System.out.println();
for (int i = 0; i < 8; i++) {
System.out.println("Enter Subject " + (i + 1) + " details");
String subjectAndGrade = in.next();
int index = subjectAndGrade.lastIndexOf(" ");
String subject = subjectAndGrade.substring(0, index);
int grade = Integer.parseInt(subjectAndGrade.substring(index + 1));
student.getSubjects().add(new Subject(grade, subject));
}
System.out.println("Enter Grade Successful");
System.out.println("========================================================");
System.out.println("Details: ");
System.out.println("Term Type " + student.getTerm());
for(int i = 0; i< student.getSubjects().size(); i++) {
System.out.println("Subject: " + student.getSubjects().get(i).getSubjectName() + ", Grade: " + student.getSubjects().get(i).getGradeScore());
}
}
}
}
class Student {
private List<Subject> subjects = new ArrayList<>();
private TermType term;
public List<Subject> getSubjects() {
return subjects;
}
public void setSubjects(List<Subject> subjects) {
this.subjects = subjects;
}
public TermType getTerm() {
return term;
}
public void setTerm(TermType term) {
this.term = term;
}
}
class Subject {
private int gradeScore;
private String subjectName;
public Subject(int gradeScore, String subjectName) {
this.gradeScore = gradeScore;
this.subjectName = subjectName;
}
public double getGradeScore() {
return gradeScore;
}
public void setGradeScore(int gradeScore) {
this.gradeScore = gradeScore;
}
public String getSubjectName() {
return subjectName;
}
public void setSubjectName(String subjectName) {
this.subjectName = subjectName;
}
}
scanners work by separating the input into a sequence of 'tokens' and 'delimiters'. Out of the box, 'one or more whitespace characters' is the delimiter.

Need help sorting ArrayList & Calculating averages of test scores

I tried adding a new class per a suggestion I was given, which is seen at line 67. I am unsure how to link the new class with the entries created from user input and the goal is to sort the ArrayList by the last name and to calculate averages of each of the entries 4 test scores, resulting in an average score - I would like the average score to be added to each students entry and added to the final ArrayList
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;
//information given by user input that will eventually go into the ArrayList
public class studentInformation {
public static <T> void main(String[] args) {
//creating ArrayList to hold the objects created above
ArrayList<Object> studentdatabase = new ArrayList<Object>();
char cont;
do {
Scanner fnInput = new Scanner(System.in);
System.out.println("Enter Student's First Name & Press Enter");
//String fn = fnInput.nextLine();
studentdatabase.add(fnInput.nextLine());
Scanner lnInput = new Scanner(System.in);
System.out.println("Enter Student's Last Name & Press Enter");
//String ln = lnInput.nextLine();
studentdatabase.add(lnInput.nextLine());
Scanner score1Input = new Scanner(System.in);
System.out.println("Enter Student's First Exam Score & Press Enter");
//int score1 = score1Input.nextInt();
studentdatabase.add(score1Input.nextInt());
Scanner score2Input = new Scanner(System.in);
System.out.println("Enter Student's Second Exam Score & Press Enter");
//int score2 = score2Input.nextInt();
studentdatabase.add(score2Input.nextInt());
Scanner score3Input = new Scanner(System.in);
System.out.println("Enter Student's Third Exam Score & Press Enter");
//int score3 = score3Input.nextInt();
studentdatabase.add(score3Input.nextInt());
Scanner score4Input = new Scanner(System.in);
System.out.println("Enter Student's Fourth/Final Exam Score & Press Enter");
//int score4 = score4Input.nextInt();
studentdatabase.add(score4Input.nextInt());
Scanner continueInput = new Scanner(System.in);
System.out.println("Enter 'C' to end or 'A' to Add More");
cont = continueInput.next().charAt(0);
//calculate the average score for each student
//sort the ArrayList prior to printing
//Collections.sort(studentdatabase);
//Prints out the arrayList
System.out.println(studentdatabase);
}
while(cont != 'c' || cont != 'C');
}
class Students {
String firstName, lastName;
int firstScore, secondScore, thirdScore, fourthScore, averagescore;
char lettergrade;
}
}

Fisrt, create a real Student class (singular, not plural). An instance of this class is only one student. It will handle average calculation in a dedicated method.
Think about using getters and setters with the correct accessors on your attributes.
public class Student {
private String firstName, lastName;
private int firstScore, secondScore, thirdScore, fourthScore, averagescore;
private char lettergrade;
public float computeAverage(){
int sum = firstScore + secondScore + thirdScore + fourthScore;
return (float) sum / 4;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public int getFirstScore() {
return firstScore;
}
public void setFirstScore(int firstScore) {
this.firstScore = firstScore;
}
public int getSecondScore() {
return secondScore;
}
public void setSecondScore(int secondScore) {
this.secondScore = secondScore;
}
public int getThirdScore() {
return thirdScore;
}
public void setThirdScore(int thirdScore) {
this.thirdScore = thirdScore;
}
public int getFourthScore() {
return fourthScore;
}
public void setFourthScore(int fourthScore) {
this.fourthScore = fourthScore;
}
public int getAveragescore() {
return averagescore;
}
public void setAveragescore(int averagescore) {
this.averagescore = averagescore;
}
public char getLettergrade() {
return lettergrade;
}
public void setLettergrade(char lettergrade) {
this.lettergrade = lettergrade;
}
}
Then, don't use Object in your list but Student. You created an object. Use it !
You can't sort the list until you're done with feeding it. Put the sort out of the loop.
cont != 'c' || cont != 'C'
will always be true. So you will never get out of your loop.
Finally, I would suggest something like this.
import java.util.ArrayList;
import java.util.Comparator;
import java.util.Scanner;
public class Main {
public static <T> void main(String[] args) {
//creating ArrayList to hold the objects created above
ArrayList<Student> studentdatabase = new ArrayList<Student>();
char cont;
do {
Student currentStudent = new Student();
Scanner fnInput = new Scanner(System.in);
System.out.println("Enter Student's First Name & Press Enter");
currentStudent.setFirstName(fnInput.nextLine());
Scanner lnInput = new Scanner(System.in);
System.out.println("Enter Student's Last Name & Press Enter");
currentStudent.setLastName(lnInput.nextLine());
Scanner score1Input = new Scanner(System.in);
System.out.println("Enter Student's First Exam Score & Press Enter");
currentStudent.setFirstScore(score1Input.nextInt());
Scanner score2Input = new Scanner(System.in);
System.out.println("Enter Student's Second Exam Score & Press Enter");
currentStudent.setSecondScore(score2Input.nextInt());
Scanner score3Input = new Scanner(System.in);
System.out.println("Enter Student's Third Exam Score & Press Enter");
currentStudent.setThirdScore(score3Input.nextInt());
Scanner score4Input = new Scanner(System.in);
System.out.println("Enter Student's Fourth/Final Exam Score & Press Enter");
currentStudent.setFourthScore(score4Input.nextInt());
studentdatabase.add(currentStudent);
Scanner continueInput = new Scanner(System.in);
System.out.println("Enter 'C' to end or 'A' to Add More");
cont = continueInput.next().charAt(0);
//Prints out the arrayList
System.out.println(studentdatabase);
}
while(cont != 'c' && cont != 'C');
//sort the arrayList prior to printing
studentdatabase.sort(Comparator.comparing(Student::getLastName));
//studentdatabase.sort(Comparator.comparing(Students::getLastName).reversed());
for (Student student:studentdatabase) {
System.out.println(student.getLastName() + " " + student.getFirstName() + " : " + student.computeAverage());
}
}
}

HashMap returning null after adding values

I know this question has been asked before but I can't understand how to fix this issue. I'm adding values to a HashMap and in setStudent and then when I try to change the value in replaceName but the key doesn't seem to exist.
import java.util.*;
public class Student {
private HashMap<String, List<String>> studentDetails = new HashMap<String, List<String>>();
private HashMap<String, List<String>> studentModules = new HashMap<String, List<String>>();
public void setStudent(String id, String name, String postalAddress, String emailAddress, String degreeTitle, String dateEnrolled, List<String> modules) {
List<String> information = new ArrayList<>();
information.add(name);
information.add(postalAddress);
information.add(emailAddress);
information.add(degreeTitle);
information.add(dateEnrolled);
studentDetails.put(id, information);
studentModules.put(id, modules);
}
public List<String> getStudentDetails(String x) {
return studentDetails.get(x);
}
public List<String> getStudentModules(String x) {
return studentModules.get(x);
}
public void replaceName(String id, String name, String postalAddress, String emailAddress, String degreeTitle, String dateEnrolled) {
List<String> information = new ArrayList<>();
information.add(name);
information.add(postalAddress);
information.add(emailAddress);
information.add(degreeTitle);
information.add(dateEnrolled);
studentDetails.replace(id, information);
}
}
My main class is quite long but basically it takes user input to get the values:
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner source = new Scanner(System.in);
RecordManager r = new RecordManager();
Module m = new Module();
Student s = new Student();
ChangeName c = new ChangeName();
while (true) {
System.out.println("Please enter the student id:");
r.setId(source.nextLine());
System.out.println("Please enter the student name:");
r.setName(source.nextLine());
System.out.println("Please enter the student address:");
r.setAddress(source.nextLine());
System.out.println("Please enter the student email address:");
r.setEmailAddress(source.nextLine());
System.out.println("Please enter the degree title:");
r.setDegreeTitle(source.nextLine());
System.out.println("Please enter the date enrolled:");
r.setDateEnrolled(source.nextLine());
List<String> a = new ArrayList<>();
while (true) {
System.out.println("Please enter the module name:");
String name = source.nextLine();
m.setName(name);
a = r.addModule(name, a);
m.setTitle(name);
System.out.println("Please enter the module code:");
m.setCode(source.nextLine());
while (true) {
System.out.println("Please enter the module mark (between 1 and 100):");
int mark = source.nextInt();
if (mark > 0 && mark <101) {
m.setMark(mark);
break;
}
else {
System.out.println("Module mark must be between 1 and 100");
}
}
System.out.println("Please enter the module credits:");
m.setCredits(source.nextInt());
m.setModule();
System.out.println("Would you like to enter another module? (Y/N)");
String more = source.next();
if (more.equalsIgnoreCase("N")) {
break;
}
source.nextLine();
}
r.setModules(a);
s.setStudent(r.getId(), r.getName(), r.getAddress(), r.getEmailAddress(), r.getDegreeTitle(), r.getDateEnrolled(), r.getModules());
r.addStudents(r.getId(), s.getStudentDetails(r.getId()));
System.out.println("Would you like to enter the details for another student? (Y/N)");
String another = source.next();
if (another.equalsIgnoreCase("N")) {
break;
}
source.nextLine();
}
while (true) {
System.out.println("Full list of students and details (1) \nLookup a student by name (2) \nChange student name (3)");
source.nextLine();
int choice = source.nextInt();
if (choice == 1) {
for (String id : r.getStudents().keySet()) {
System.out.println(s.getStudentDetails(id) + " " + s.getStudentModules(id));
}
break;
}
else if (choice == 2) {
System.out.println("Please enter the full name of the student:");
source.nextLine();
String name = source.nextLine();
boolean exists = false;
int i = 0;
for (String id : r.getStudents().keySet()) {
if (s.getStudentDetails(id).get(i).equalsIgnoreCase(name)) {
System.out.println(s.getStudentDetails(id) + " " + s.getStudentModules(id));
exists = true;
}
i += 1;
}
if (exists == false) {
System.out.println("Student not found");
}
break;
}
else if (choice == 3) {
System.out.println("Please enter the ID of the student:");
source.nextLine();
String id = source.nextLine();
System.out.println("Please enter the new name:");
String name = source.nextLine();
c.changeName(id, name, s.getStudentDetails(id));
System.out.println(s.getStudentDetails(id));
break;
}
else {
System.out.println("Incorrect selection. Please enter 1, 2 or 3");
}
}
}
}
And finally I have the class to change the name:
import java.util.*;
public class ChangeName {
RecordManager r = new RecordManager();
Student s = new Student();
public void changeName(String id, String newName, List<String> details) {
s.replaceName(id, newName, details.get(1), details.get(2), details.get(3), details.get(4));
}
}
Any help would be greatly appreciated!!

How do i use user input for a string array that is in a while loop?

I'm trying to convert the user input from the question of students name and score into a array.
I also need help to printout the array.
The while loop is using boolean loopNaming as its condition, and i is updated everytime the loop occurs.
public static void main(String [] args)
{
Scanner keyboard = new Scanner(System.in);
double score;
boolean loopNaming=true;
int i=0;
String[] name = new String[i];
while(loopNaming==true)
{
System.out.printf("Enter name of student or done to finish: ");
name[i] = keyboard.next();
if(name[i].equals("done"))
{
loopNaming = false;
}
else
{
System.out.println("Enter score: ");
score = keyboard.nextDouble();
}
i=i+1;
}
System.out.println(name[i]);
}
}

You can simplify the logic of your program and write something like this,
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
List<String> nameList = new ArrayList<String>();
List<Double> scoreList = new ArrayList<Double>();
while (true) {
System.out.printf("Enter first name of student or done to finish: ");
String fname = keyboard.next();
if (fname.equals("done")) {
break;
}
System.out.printf("Enter last name of student: ");
String lname = keyboard.next();
nameList.add(fname + " " + lname);
System.out.println("Enter score: ");
scoreList.add(keyboard.nextDouble());
}
keyboard.close();
System.out.println("Names: " + nameList);
System.out.println("scores: " + scoreList);
}

I have changed the array to an arraylist and moved i=i+1; to inside else segment. Also changed the final print statement to print the list.
public static void main(String [] args)
{
Scanner keyboard = new Scanner(System.in);
double score;
boolean loopNaming=true;
int i=0;
ArrayList<String> name = new ArrayList<String>();
while(loopNaming==true)
{
System.out.printf("Enter name of student or done to finish: ");
name.add(keyboard.next());
if(name.get(i).equals("done"))
{
loopNaming = false;
}
else
{
System.out.println("Enter score: ");
score = keyboard.nextDouble();
i=i+1;
}
}
System.out.println(name);
}

I would firstly recommend using a List data structure:
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
double score;
boolean loopNaming = true;
List<String> name = new ArrayList<>();
while (loopNaming) {
System.out.printf("Enter name of student or done to finish: ");
String input = keyboard.next();
if (input.equals("done")) {
loopNaming = false;
} else {
name.add(input);
System.out.println("Enter score: ");
score = keyboard.nextDouble();
}
}
System.out.println(name.toString());
}
However, if you very much would like to use an array, you could make your own method to increase the size of your array each time a new name is added:
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
double score;
int i = 0;
boolean loopNaming = true;
String[] name = {};
while (loopNaming) {
System.out.printf("Enter name of student or done to finish: ");
String input = keyboard.next();
if (input.equals("done")) {
loopNaming = false;
} else {
name = increaseArray(name);
name[i] = input;
System.out.println("Enter score: ");
score = keyboard.nextDouble();
i++;
}
}
System.out.println(Arrays.toString(name));
}
public static String[] increaseArray(String[] arr) {
String[] temp = new String[arr.length + 1];
for (int i = 0; i < arr.length; i++) {
temp[i] = arr[i];
}
return temp;
}
I was unsure what your plan was with your score variable, but this would be two ways to achieve your desired result.
I hope this helps.

public static void main(String [] args)
{
Scanner keyboard = new Scanner(System.in);
double score;
boolean loopNaming=true;
int i=0;
ArrayList<String> name = new ArrayList<>();
while(loopNaming==true)
{
System.out.printf("Enter name of student or done to finish: ");
String input = keyboard.next();
if(input.equals("done"))
{
loopNaming = false;
}
else
{ name.add(input);
System.out.println("Enter score: ");
score = keyboard.nextDouble();
}
i=i+1; //no need to use
}
System.out.println(name);
}
You should use a dynamic list because You can't resize an array in Java. The second point when the user gives "done", you should not put it in the list so check it before the insertion.

You declared your String array with size 0. that's why you cant add elements in to it.
import java.util.Scanner;
public class NameArray {
public static void main(String [] args){
Scanner keyboard = new Scanner(System.in);
double score[] = new double[10];
boolean loopNaming=true;
int i=0;
String namae;
String[] name = new String[10];
int count = 0;
while(loopNaming==true){
System.out.printf("Enter name of student or done to finish: ");
name[i] = keyboard.next();
if(name[i].equals("done")){
loopNaming = false;
}
else{
System.out.println("Enter score: ");
score[i] = keyboard.nextDouble();
count++;
}
i=i+1;
}
for(int j = 0; j < count; j++) {
System.out.println(name[j]+" "+score[j]);
}
}
}
Try this code or you can go for any other data structures.

Java Programming String Array Trouble

import java.util.Scanner;
public class GradePointAverage {
public static void main(String[] args) {
Scanner peace = new Scanner(System.in);
System.out.print("How many subjects do you want to enter?: ");
int a=peace.nextInt();
String[] b = new String[a];
for(int i=0;i<a;i++) {
b[i]="";
System.out.print("Enter Subject No "+(i+1)+" ");
String c=peace.next();
}
for(i=0;i<b.length;i++) {
System.out.print(b[i]);
}
}
}
Greetings. :)
We have a programming experiment and well I was stuck in this part. I need to ask the user how many subjects he wants to enter and ask the user to input the subjects. I think I already entered the subjects on the array but when i want to see the content of the array it won't give me my desired output, the subjects i entered won't appear. Please help, I'm new here on this site and it's my first time to ask a question on a forum like this. Hoping that someone would reply. Thanks.

You never put the subject into the array.
import java.util.Scanner;
public class GradePointAverage
{
public static void main(String[] args)
{
int i;
Scanner peace=new Scanner(System.in);
System.out.print("How many subjects do you want to enter?: ");
int a=peace.nextInt();
String []b=new String [a];
for(i=0;i<a;i++)
{
System.out.print("Enter Subject No "+(i+1)+" ");
b[i]=peace.next();
}
for(i=0;i<b.length;i++)
{
System.out.print(b[i]);
}
}
}

You never assign the Strings to the array.
Change
String c=peace.next();
to
b[i] = peace.next();
In addition, you should probably add some separator (or new line) when printing the array :
public static void main(String[] args)
{
Scanner peace = new Scanner(System.in);
System.out.print("How many subjects do you want to enter?: ");
int a = peace.nextInt();
String[] b = new String[a];
for(int i = 0; i < a; i++) {
System.out.print("Enter Subject No " + (i + 1) + " ");
b[i] = peace.next();
}
for(i = 0; i < b.length; i++) {
System.out.print(b[i] + " ");
}
}

import java.util.Scanner;
public class GradePointAverage
{
public static double processAverage(int []SubjectGrades,int SubjectsNumber)
{
double sum=0;
double Ave=0;
for(int i=0;i<SubjectGrades.length;i++)
{
sum=SubjectGrades[i]+sum;
}
Ave=sum/SubjectsNumber;
return Ave;
}
public static int processNumericalValue(double Ave)
{
int Numeral;
if(Ave>=98.0&&Ave<100.0)
{
Numeral=4;
}
else if(Ave>=90.0&&Ave<98.0)
{
Numeral=3;
}
else if(Ave>=80.0&&Ave<90.0)
{
Numeral=2;
}
else if(Ave>=75.0&&Ave<80.0)
{
Numeral=1;
}
else
{
Numeral=0;
}
return Numeral;
}
public static void processLetterGrade(int Numeral)
{
if(Numeral==4)
{
System.out.println("Congratulations!");
}
else if(Numeral==3)
{
System.out.println("Your Letter Grade is B!");
}
else if(Numeral==2)
{
System.out.println("Your Letter Grade is C!");
}
else if(Numeral==1)
{
System.out.println("Your Letter Grade is D!");
}
else
{
System.out.println("You Failed!");
}
}
public static void main(String[] args)
{
double Ave=0;
Scanner peace=new Scanner(System.in);
System.out.print("How many subjects do you want to enter?: ");
int SubjectsNumber=peace.nextInt();
int []SubjectGrades=new int [SubjectsNumber];
String []Subjects=new String [SubjectsNumber];
for(int i=0;i<SubjectsNumber;i++)
{
Subjects[i]="";
System.out.print("Enter Subject No "+(i+1)+": ");
Subjects[i]=peace.next();
System.out.println("What is your grade in "+Subjects[i]+": ");
SubjectGrades[i]=peace.nextInt();
}
int Numeral;
Ave=processAverage(SubjectGrades,SubjectsNumber);
System.out.println("Your General Average is: "+Ave);
Numeral=processNumericalValue(Ave);
System.out.println("Numerical Value is: "+Numeral);
processLetterGrade(Numeral);
}
}