I created a user defined data type and read data from a file. Here are the codes:
Student Class:
package system.data;
public class Student {
private String firstName;
private String lastName;
private String regNumber;
private int coursework1Marks;
private int coursework2Marks;
private int finalExamMarks;
private double totalMarks;
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 String getRegNumber() {
return regNumber;
}
public void setRegNumber(String regNumber) {
this.regNumber = regNumber;
}
public int getCoursework1Marks() {
return coursework1Marks;
}
public void setCoursework1Marks(int coursework1Marks) {
this.coursework1Marks = coursework1Marks;
}
public int getCoursework2Marks() {
return coursework2Marks;
}
public void setCoursework2Marks(int coursework2Marks) {
this.coursework2Marks = coursework2Marks;
}
public int getFinalExamMarks() {
return finalExamMarks;
}
public void setFinalExamMarks(int finalExamMarks) {
this.finalExamMarks = finalExamMarks;
}
public double getTotalMarks() {
totalMarks = (coursework1Marks * 0.2) + (coursework2Marks * 0.2) + (finalExamMarks * 0.6);
return totalMarks;
}
}
And the main coding:
public class MainInterface extends javax.swing.JFrame {
private File studentFile = new File(".\\StudentMarks.txt");
private PrintWriter printWriter = null;
private FileOutputStream fileOutputStream = null;
public ArrayList<Student> studentDetails = null;
private Scanner input = null;
private int counter = 0;
/**
* Creates new form MainInterface
*/
public MainInterface() {
initComponents();
setLocationRelativeTo(null);
studentDetails = new ArrayList<Student>();
ReadStudentDetails(studentDetails);
}
private void ReadStudentDetails(ArrayList<Student> studentDetails) {
ArrayList<String> strList = new ArrayList<>();
Student student = new Student();
try {
input = new Scanner(studentFile);
} catch (FileNotFoundException ex) {
Logger.getLogger(MainInterface.class.getName()).log(Level.SEVERE, null, ex);
}
while(input.hasNext()){
counter++;
String str = input.nextLine();
strList.add(str);
System.out.println(counter);
}
for (String item : strList) {
int x = 0;
String[] arr = item.split(":");
student.setFirstName(arr[0]);
student.setLastName(arr[1]);
student.setRegNumber(arr[2]);
student.setCoursework1Marks(Integer.parseInt(arr[3]));
student.setCoursework2Marks(Integer.parseInt(arr[4]));
student.setFinalExamMarks(Integer.parseInt(arr[5]));
studentDetails.add(student);
}
}
There no syntax errors given. But When I try to print the elements in the ArrayList as,
for(Student item: studentDetails){
System.out.println(item.getFirstName());
}
It gives out only the last record from the file, (which has 3 records). Why is this happening? Thanks in advance.
The same student object is reused, because Java passes a reference to an object in the call that adds the student to the list. In other words, the original student is passed each time. The solution is to create a new Student for each call.
for (String item : strList) {
int x = 0;
String[] arr = item.split(":");
Student student = new Student();
student.setFirstName(arr[0]);
student.setLastName(arr[1]);
student.setRegNumber(arr[2]);
student.setCoursework1Marks(Integer.parseInt(arr[3]));
student.setCoursework2Marks(Integer.parseInt(arr[4]));
student.setFinalExamMarks(Integer.parseInt(arr[5]));
studentDetails.add(student);
}
create new instance of Student object inside the for loop
like this
for (String item : strList) {
int x = 0;
String[] arr = item.split(":");
Student student = new Student();
student.setFirstName(arr[0]);
student.setLastName(arr[1]);
student.setRegNumber(arr[2]);
student.setCoursework1Marks(Integer.parseInt(arr[3]));
student.setCoursework2Marks(Integer.parseInt(arr[4]));
student.setFinalExamMarks(Integer.parseInt(arr[5]));
studentDetails.add(student);
}
Actually you are always using the same student object.You have to put Student student = new Student(); inside the for loop.
try moving Student student = new Student(); inside the for loop:
for (String item : strList) {
int x = 0;
String[] arr = item.split(":");
Student student = new Student();
student.setFirstName(arr[0]);
student.setLastName(arr[1]);
student.setRegNumber(arr[2]);
student.setCoursework1Marks(Integer.parseInt(arr[3]));
student.setCoursework2Marks(Integer.parseInt(arr[4]));
student.setFinalExamMarks(Integer.parseInt(arr[5]));
studentDetails.add(student);
}
hope this helps.
Related
I am new in java and I trying to get information
for five students and save them into an array of classes. how can I do this?
I want to use class person for five students whit different informations
import java.io.IOException;
import java.util.*;
public class exam
{
public static void main(String[] args)
{
Scanner s = new Scanner(System.in);
// I want to get and save information in this array
person[] f = new student[5];
}
}
class person defined for get name and family name.
import java.util.*;
public abstract class person {
Scanner scr = new Scanner(System.in);
private String name , fname;
public void SetName() {
System.out.println("enter name and familyNAme :");
name = scr.next();
}
public String getname() {
return name;
}
public void setfname () {
System.out.println("enter familyname:");
fname = scr.next();
}
public String getfname() {
return fname;
}
}
class student that inherits from the class person for get studentID and student Scores .
import java.util.*;
class student extends person {
float[] p = new float[5];
int id , sum ;
float min;
public void inputs() {
System.out.println("enter the id :");
id = scr.nextInt();
}
public void sumation() {
System.out.println("enter points of student:");
sum= 0;
for(int i = 0 ; i<5 ; i++){
p[i]=scr.nextFloat();
sum+=p[i];
}
}
public void miangin() {
min = (float)sum/4;
}
}
So first things first, when creating Java objects, refrain from getting input inside the object so that if you decide to change the way you get input (e.g. transition from command line to GUI) you don't need to modify the Java object.
Second, getters and setters should only get or set. This would save some confusion when debugging since we don't have to check these methods/functions.
So here's the person object:
public abstract class Person {
protected String name, fname;
public Person (String name, String fname) {
this.name = name;
this.fname = fname;
}
public void setName (String name) {
this.name = name;
}
public String getName () {
return name;
}
public void setFname (String fname) {
this.fname = fname;
}
public String getFname () {
return fname;
}
}
And here's the student object (tip: you can make as much constructors as you want to make object creation easier for you):
public class Student extends Person {
private float[] p;
private int id;
public Student (String name, String fname) {
this (name, fname, -1, null);
}
public Student (String name, String fname, int id, float[] p) {
super (name, fname);
this.id = id;
this.p = p;
}
public void setP (float[] p) {
this.p = p;
}
public float[] getP () {
return p;
}
public void setId (int id) {
this.id = id;
}
public int getId () {
return id;
}
public float summation () {
float sum = 0;
for (int i = 0; i < p.length; i++)
sum += p[i];
return sum;
}
public float miangin () {
return summation () / 4.0f;
}
#Override
public String toString () {
return new StringBuilder ()
.append ("Name: ").append (name)
.append (" Family name: ").append (fname)
.append (" Id: ").append (id)
.append (" min: ").append (miangin ())
.toString ();
}
}
And lastly, wherever your main method is, that is where you should get input from. Take note that when you make an array, each index is initialized to null so you still need to instantiate each array index before using. I made a sample below but you can modify it depending on what you need.
import java.util.*;
public class Exam {
Scanner sc;
Person[] people;
Exam () {
sc = new Scanner (System.in);
people = new Person[5];
}
public void getInput () {
for (int i = 0; i < people.length; i++) {
System.out.print ("Enter name: ");
String name = sc.nextLine ();
System.out.print ("Enter family name: ");
String fname = sc.nextLine ();
System.out.print ("Enter id: ");
int id = sc.nextInt (); sc.nextLine ();
System.out.println ("Enter points: ");
float[] points = new float[5];
for (int j = 0; j < points.length; j++) {
System.out.printf ("[%d] ", j + 1);
points[j] = sc.nextFloat (); sc.nextLine ();
}
people[i] = new Student (name, fname, id, points);
}
}
public void printInput () {
for (Person p: people)
System.out.println (p);
}
public void run () {
getInput ();
printInput ();
}
public static void main (String[] args) {
new Exam ().run ();
}
}
Just one last tip, if you ever need dynamic arrays in Java, check out ArrayList.
You can add a class attribute, and then add class information for each student, or you can add a class class, define an array of students in the class class, and add an add student attribute, and you can add students to that class.
First of all, please write class names with capital letter (Student, Exam <...>).
Exam class:
import java.util.Scanner;
public class Exam {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
Student[] students = new Student[]{
new Student(),
new Student(),
new Student(),
new Student(),
new Student()
};
for (int i = 0; i < 5; i++) {
students[i].setFirstName();
students[i].setLastName();
students[i].setId();
}
}
}
Person class:
import java.util.Scanner;
public class Person {
String firstName, lastName;
public String getFirstName() {
return firstName;
}
public void setFirstName() {
System.out.println("Type firstName: ");
this.firstName = new Scanner(System.in).next();
}
public String getLastName() {
return lastName;
}
public void setLastName() {
System.out.println("Type lastName: ");
this.lastName = new Scanner(System.in).next();
}
}
Student class:
import java.util.Scanner;
public class Student extends Person{
int id;
public int getId() {
return id;
}
public void setId() {
//Converting String line into Integer by Integer.parseInt(String s)
System.out.println("Type id: ");
this.id = Integer.parseInt(new Scanner(System.in).next());
}
}
I'm trying to add order1 object to orderList in the Customer class, but it's not working. The toString() method returns zero items in the ArrayList. Does anyone have any idea of what else I can try doing instead?
public class Customer {
private ArrayList<Order> orderList;
private int numberOfOrders = 0;
public Customer(String name, Order firstElementInList) {
this(name);
this.orderList.add(0, firstElementInList);
}
public void setNumberOfOrders() {
this.numberOfOrders = orderList.size();
}
public String toString() {
return name + numberOfOrders;
}
}
public class Main {
static Scanner scan = new Scanner(System.in);
public static void main(String[] args) {
Order order1 = new Order( "bob", 1.1 );
Customer bob = new Customer( "Bobby Shmurda ", order1 );
System.out.println(bob.toString());
}
}
A String Object gets added to ArrayList and when toString() is invoked should return the length of the ArrayList.
Because your list is yet to be created as you have not created its object.
Use below code to create your list.
private ArrayList<Order> orderList = new ArrayList<>();
public class Customer {
private List<Order> orderList;
private int numberOfOrders = 0;
public Customer(String name, Order firstElementInList) {
this(name);
if(orderList == null) {
orderList = new ArrayList<Order>();
}
this.orderList.add(0, firstElementInList);
}
public void setNumberOfOrders() {
this.numberOfOrders = orderList.size();
}
public String toString() {
return "The length of the orderList: " + orderList != null ? orderList.size() : 0;
}
}
public class Main {
static Scanner scan = new Scanner(System.in);
public static void main(String[] args) {
Order order1 = new Order( "bob", 1.1 );
Customer bob = new Customer( "Bobby Shmurda ", order1 );
System.out.println(bob.toString());
}
}
Here is the method in the driver:
public class CustomerTest {
private static int customerCounter = 0;
public static boolean test1(){
System.out.println("Test1: create a customer");
Customer c = new Customer("Alice", "Smith");
customerCounter++;
return c.getName().equals("Alice Smith") && customerCounter == c.getCustomerID();
}
public static boolean test2() {
System.out.println("Test2: create two customers");
Customer c1 = new Customer("Alice", "Smith");
Customer c2 = new Customer("Bob", "Simpson");
customerCounter += 2;
return c1.getName().equals("Alice Smith") && (customerCounter - 1) == c1.getCustomerID()
&& c2.getName().equals("Bob Simpson") && (customerCounter) == c2.getCustomerID();
}
public static void main(String[] args) {
String result = "";
//System.out.print("Test 1: ");
result = test1() ? "pass." : "failed.";
System.out.println(result);
//System.out.print("Test 2: ");
result = test2() ? "pass." : "failed.";
System.out.println(result);
}
}
Here is code I've written:
public class Customer {
public static final int MAX_ACCOUNTS = 5;
private String firstName;
private String lastName;
private int customerID;
private BankAccount[] accounts;
private int numAccounts;
private static int nextCustomerID = 1;
//default constructor
public Customer() {
firstName = "";
lastName = "";
customerID = 1;
accounts = null;
numAccounts = 0;
nextCustomerID = 1;
}
//Constructor sets name and initialized values
//#param first is the first name
//#param last is the last name
public Customer (String first, String last)
{
this.firstName = first;
this.lastName = last;
this.customerID = 1;
Customer.nextCustomerID = 1;
}
public String getFirst(){
return firstName;
}
public String getLast(){
return lastName;
}
public String getName ()
{
return String.format("%s,%s", getFirst(),getLast());
}
public int getCustomerID ()
{
return customerID;
}
}
When I run the driver it returns failed. I can't seem to see why, everything seems to be in place correctly. The only thing I can think of is a problem with String.format
I have two classes; Course and Student classes. One of the fields in the Student class is a course. When i run this program, I fail to hold a course object in the declared array. The code below will give more light where things are failing:
package school;
public class Course
{
private String courseName;
private String courseGrade;
int counter;
public Course()
{
courseName="";
courseGrade="";
counter = 0;
}
public Course (String name,String grade)
{
courseName=name;
courseGrade=grade;
counter=0;
}
public String getCourseName()
{
return courseName;
}
public String getCourseGrade()
{
return courseGrade;
}
public void setCourse(String name,String grade)
{
courseName=name;
courseGrade=grade;
counter++;
}
#Override
public String toString ()
{
return String.format("%-10s %-10s", courseName,courseGrade);
}
}
package school;
public class Student
{
private String firstName;
private String lastName;
private int counter;
private Course [] myCourse;
public Student ()
{
firstName="";
lastName="";
myCourse =new Course[2];
for (int i=0;i<2;i++)
{
myCourse [i]= new Course ();
}
counter= 0;
}
public Student(String first,String last)
{
firstName=first;
lastName=last;
myCourse =new Course[2];
for (int i=0;i<2;i++)
{
myCourse [i]= new Course ();
}
counter= 0;
}
public Student(String first,String last, Course [] newCourse)
{
firstName=first;
lastName=last;
myCourse= new Course [2];
for (int i=0;i<2;i++)
{
myCourse [i]= new Course ();
}
counter++;
}
public String getFirstName()
{
return firstName;
}
public String getLastName()
{
return lastName;
}
public int getNumberOfCourses()
{
return counter;
}
public void setStudent(String first,String last, Course [] newCourse)
{
firstName=first;
lastName=last;
myCourse= new Course [2];
for (int i=0;i<2;i++)
{
myCourse [i]= newCourse[i];
}
counter++;
}
public void setStudent(String first,String last)
{
firstName=first;
lastName=last;
}
public void registerCourses(Course newCourse)
{
for (int i=0;i<2;i++)
{
myCourse[i]=newCourse;
}
counter++;
}
public String toString()
{
String getString;
getString =(firstName+" "+lastName);
for(int i=0;i<2;i++)
{
getString=getString+String.format("%n %-10s",myCourse[i]);
}
return getString;
}
}
package school;
import java.util.*;
public class Test
{
static Scanner cin= new Scanner(System.in);
public static void main(String[] args)
{
String first,last,name,grade;
Student [] myStudent= new Student [2];
Course [] myCourse= new Course [2];
for (int i=0;i<2;i++)
{
myStudent[i] = new Student();
System.out.println("enter name:");
first=cin.next();
System.out.println("Last Name:");
last=cin.next();
// For loop within a for loop
for (int j=0;j<2;j++)
{
myCourse [j]= new Course ();
System.out.println("Course Name:");
name=cin.next();
System.out.println("Course Grade:");
grade=cin.next();
myCourse [j] = new Course(name,grade);
myStudent[i].registerCourses(myCourse [j]);
}
myStudent [i]=new Student(first, last, myCourse);
}
for (int i=0;i<2;i++)
{
System.out.println(myStudent[i]);
}
}
}
the problem is in the second for loop which is unable to hold course object that i want it to.
I want the program to output something similar to the following:
Student One
MAT A
PHY B
BIO C
CHE A
LAN A+
HIS A
Student Two
COM C
Statistics A+
COM C
Mathematics D
Geography A
Biology C+
Student Three
Biology C
Mathematics D
LAN A+
COM B
Physics B
Physics B
However I am unable to obtain that output. In fact i get the following output:
enter name:
Student
Last Name:
One
Course Name:
MAT
Course Grade:
A
Course Name:
COM
Course Grade:
C
enter name:
Student
Last Name:
Two
Course Name:
STA
Course Grade:
A
Course Name:
ENG
Course Grade:
B
Student One
Student Two
you are destroying the first myStudent[i] data when performing a new on the same index at the end of your loop:
for (int i=0;i<2;i++)
{
myStudent[i] = new Student();
<some code>
myStudent [i]=new Student(first, last, myCourse);
Since you have an undefined number of courses I would suggest using ArrayList and then you do
Also, think what you are doing here.
public void registerCourses(Course newCourse)
{
for (int i=0;i<2;i++)
{
myCourse[i]=newCourse;
}
counter++;
}
You are adding one course and then saying for each position for a course in my array add the new course I was given
You should either use an index, or use an arraylist, or linkedlist etc.
E.g.
public void registerCourses(Course newCourse, int index)
{
myCourse[index]=newCourse;
}
or
public void registerCourses(Course newCourse)
{
myCourse.push(newCourse); // that is given myCourse is an ArrayList<Course>
}
Check the registerCourses method inside Student class. It seems its overriding your result on a same index.
You can do that with List and keep adding that.
Here is the one I updated Student Class.
package com.stack;
import java.util.ArrayList;
import java.util.List;
public class Student
{
private String firstName;
private String lastName;
private int counter;
private List<Course> myCourse;
public Student ()
{
firstName="";
lastName="";
myCourse =new ArrayList<Course>();
counter= 0;
}
public Student(String first,String last)
{
firstName=first;
lastName=last;
myCourse =new ArrayList<Course>();
counter= 0;
}
public Student(String first,String last, List<Course> newCourse)
{
firstName=first;
lastName=last;
myCourse= newCourse;
counter++;
}
public String getFirstName()
{
return firstName;
}
public String getLastName()
{
return lastName;
}
public int getNumberOfCourses()
{
return counter;
}
public void setStudent(String first,String last, List<Course> newCourse)
{
firstName=first;
lastName=last;
myCourse= newCourse;
counter++;
}
public void setStudent(String first,String last)
{
firstName=first;
lastName=last;
}
public void registerCourses(Course newCourse)
{
myCourse.add(newCourse);
counter++;
}
public String toString()
{
String getString;
getString =(firstName+" "+lastName);
for(int i=0;i<2;i++)
{
getString=getString+String.format("%n %-10s",myCourse.get(i));
}
return getString;
}
}
Test Class:
package com.stack;
import java.util.*;
public class Test
{
static Scanner cin= new Scanner(System.in);
public static void main(String[] args)
{
String first,last,name,grade;
Student [] myStudent= new Student [2];
List<Course> myCourse= new ArrayList<Course>();
for (int i=0;i<2;i++)
{
myStudent[i] = new Student();
System.out.println("enter name:");
first=cin.next();
System.out.println("Last Name:");
last=cin.next();
// For loop within a for loop
for (int j=0;j<2;j++)
{
System.out.println("Course Name:");
name=cin.next();
System.out.println("Course Grade:");
grade=cin.next();
Course myC = new Course(name,grade);
myCourse.add(myC);
myStudent[i].registerCourses(myC);
}
myStudent [i]=new Student(first, last, myCourse);
}
for (int i=0;i<2;i++)
{
System.out.println(myStudent[i]);
}
}
}
Note: For 3 Students, you need to iterate loop until i<3 (not 2).
Im creating a program that is supposed have the user enter a student name and see if it exist in the student array using a linear search method. The student array is in a different class and im having trouble creating a constructor i have tried many things and its not working can someone point me in the right direction.
My linear search class is
import java.util.*;
import java.util.Scanner;
public class LinearSearch {
public int find(Student [] a, String nm) {
for (int i = 0; i < a.length; i++) {
if (a[i].equals(nm)){
return i;
break;
}
else{
return -1;
}
}
}
public static void main(String[] args) {
Scanner reader = new Scanner(System.in);
LinearSearch search = new LinearSearch();
Student stu = new Student();
Student [] arr = stu.getArray();
System.out.print("Enter the name to search: ");
String name = reader.nextLine();
int n = search.find(arr, name);
if ((n >= 0) && (n < arr.length)) {
System.out.println(name + " was found at index: " + n);
} else {
System.out.println(name + " was not found");
}
}
}
My Student class is
import java.util.*;
public class Student {
public Student(){
}
public Student [] getArray(){
Student [] studentArray = new Student[3];
studentArray[0] = new Student ("Mel");
studentArray[1] = new Student ("Jared");
studentArray[2] = new Student ("Mikey");
return studentArray;
}
}
You defined a constructor with no argument:
public Student() {
}
But you're invoking a constructor which needs a String as argument:
studentArray[0] = new Student("Mel");
So, your constructor should have a String as argument:
public Student(String name)
And you should probably store this name as a field in the Student class:
private String name;
public Student(String name) {
this.name = name;
}
Note that there is no way that a Student instance could be equal to a String instance. You should provide a getter method for the name, and compare the entered String with the name of the student, instead of comparing it with the student itself.
import java.util.*;
public class Student {
private String name;
public Student(String name){
this.name = name;
}
public Student [] getArray(){
Student [] studentArray = new Student[3];
studentArray[0] = new Student ("Mel");
studentArray[1] = new Student ("Jared");
studentArray[2] = new Student ("Mikey");
return studentArray;
}
public String getName(){
return name;
}
}
and of course in the compersion you'll need to do:
f (a[i].getName().equals(nm)){
public class Student {
private String studentName;
private Student[] studentArray;
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public Student[] getStudentArray() {
return studentArray;
}
public void setStudentArray(Student[] studentArray) {
this.studentArray = studentArray;
}
public Student(){
studentArray = new Student[3];
}
public Student[] getArray() {
Student st1 = new Student();
st1.setStudentName("mel");
Student st2 = new Student();
st2.setStudentName("Jared");
Student st3 = new Student();
st3.setStudentName("Mikey");
studentArray[0]=st1;
studentArray[1]=st2;
studentArray[2]=st3;
return studentArray;
}
}
the above code is your Student class. there is no need to create a constructor though. but because you would like it i put it in the code.
the LinearSearch class is as follow:
public class LinearSearch {
private int i;
public int find(Student[] a, String nm) {
for ( i = 0; i < a.length; i++) {
if (a[i].getStudentName().equals(nm)) {
break;
} else {
i = -1;
}
}
return i;
}
public static void main(String[] args) {
Scanner reader = new Scanner(System.in);
LinearSearch search = new LinearSearch();
Student stu = new Student();
Student[] arr = stu.getArray();
System.out.print("Enter the name to search: ");
String name = reader.nextLine();
int n = search.find(arr, name);
if ((n >= 0) && (n < arr.length)) {
System.out.println(name + " was found at index: " + n);
} else {
System.out.println(name + " was not found");
}
}
}