I have two different class, Student and StudentTest - the Student class has;
public class Student {
// Data Members
private String name; // The name of this student
private long idNumber; // The ID number of this student
// Constructs a new Student with passed name and ID number parameters.
public Student(String studentName, long studentIDNumber) {
name = studentName;
idNumber = studentIDNumber;
}
// Returns the name of this student.
public String getName() {
return name;
}
// Returns the ID number of this student.
public long getIDNumber() {
return idNumber;
}
// Sets the name of this student.
public void setName(String studentName) {
name = studentName;
}
// Sets the ID number of this student.
public void setIDNumber(long studentIDNumber) {
idNumber = studentIDNumber;
}
#Override
public String toString(){
return "Name: " + this.name;
}
} // end class
And the StudentTest class has 3 different methods, 1. to ask the user to enter the size of an array and then create an array of type Student, 2. to ask the user to populate the array with names and ID numbers, 3. to display the contents of the array.
import java.util.Scanner;
public class StudentTest {
// Main method.
public static void main(String [] args) {
Student[] students = createArray();
populateArray(students);
displayArray(students);
}
// Method that asks user for size of array.
public static Student[] createArray() {
System.out.println("Enter size of array: ");
Scanner userInputEntry = new Scanner(System.in);
int inputLength = userInputEntry.nextInt();
Student students[] = new Student[inputLength];
return students;
}
// Method that asks user to populate array.
public static void populateArray(Student [] array) {
for(int i = 0; i < array.length; i++) {
array[i] = new Student();
System.out.println("Enter student name: ");
Scanner userInputEntry = new Scanner(System.in);
array[i].setName(userInputEntry.next());
System.out.println("Enter student ID number: ");
array[i].setIDNumber(userInputEntry.nextLong());
}
}
// Method that displays contents of array.
public static void displayArray(Student[] array) {
for(int i = 0; i < array.length; i++){
System.out.println(array[i].toString());
}
}
}
When I try to run it, I get an error about the
array[i] = new Student();
in the for loop in the second method.
How would you expect this to work ?
#Override
public void toString(){
return "Name: " + this.name;
}
It should give you an compile error. You are trying to send a string back and the return type is void.
Change it to
#Override
public String toString(){
return "Name: " + this.name;
}
Change you main method to
// Main method.
public static void main(String [] args) {
Student[] students = createArray();
populateArray(students);
displayArray(students)
}
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 am trying to solve an assignment in my Java class. I am stuck and need a little help.
I am trying to create a method in my Group class that will display the group name and the 4 students in the group. My code currently displays the group name and the memory location of my student inside my array.
public class Group {
/**-------Declaring attributes----*/
String groupName;
int newStudentCount;
/**----------------------------*/
/**--------Constructor------------*/
public Group(String givenGroupName) {
groupName = givenGroupName;
}
Student[] students = new Student[4];
/**----------------------------*/
/**--------Method------------*/
void addStudent(Student st) {
students[newStudentCount] = st;
++newStudentCount;
System.out.println("New student: " +st.getName());
}
public String getGroup() {
return "Group = " + groupName;
}
public Student getStudent(){
return students[0];
}
}
In my App class I have this:
public class App {
public static void main(String[] args) {
Group g1 = new Group("Pink Pony Princesses");
Student st1 = new Student("Joshua Mathews");
st1.getName();
g1.addStudent(st1);
Student st2 = new Student("Jame Brooks");
g1.addStudent(st2);
Student st3 = new Student("Mike Myers");
g1.addStudent(st3);
Student st4 = new Student("Christie Richie");
g1.addStudent(st4);
System.out.println(g1.getGroup()+ " " + g1.getStudent());
}
This is my Student class:
public class Student {
/**-------Declaring attributes----*/
String name;
String degree;
int age;
/**----------------------------*/
/**--------Constructor------------*/
Student(String givenName){
name = givenName;
}
Student(String givenName, String givenDegree, int givenAge) {
name = givenName;
degree = givenDegree;
age = givenAge;
}
/**--------- METHODS --------*/
//Array
public final String [] activities = {
"Working on Homework", "Playing a Game", "Taking a Nap"
};
String getInfo(){
return name + age + degree;
}
String getName() {
return name;
}
int getAge(){
return age;
}
String getDegree() {
return degree;
}
String whatsUp(){
Random rand = new Random();
int randomIndex = rand.nextInt(activities.length);
String returnActivity = activities[randomIndex];
return returnActivity;
}
I'm not sure how to call my array to display the 4 names, and not the memory location of them. Any help would be greatly appreciated.
I can deduce a couple of things from your question.
First, you are returning only the student at index 0 of the Student array held within your Group object. If you want to return all students your method signature should have a Student[] as the return type rather than a Student object.
If you follow the above prompt then you will have to iterate through the returned array printing each Student object.
Regardless of which implementation you choose the reason you print out a memory reference rather than a String object is that you have not overridden toString within your Student class.
Something like this will print out Student data when passed to a System.out call:
#Override
public String toString() {
return someStudentData;
}
You can go with what andrewdleach said by implementing toString(). OR
To print all student names your method should be something like:
public String getStudent(){
String studentNames = "";
for(Student stu: students){
studentNames+= stu.getName() + ",";
}
return studentNames;
}
I am trying to get my addStudent() method in the Roster class to work here.
It's supposed to add a given student to this roster. If the student is already on the roster, or the numStudents == stopPoint, it doesn't change the roster and returns false. If it is successful it returns true.
Roster Class:
public class Roster {
Student[] students;
int numStudents;
int stopPoint;
Course course;
//constructor for this class initialize this roster to empty
public Roster(int stopPoint, Course course)
{
this.stopPoint = stopPoint;
this.course = course;
}
//returns a string that represents the object for printing
public String toString()
{
String res = "";
for(int j = 0; j < numStudents; j++)
{
res = res + "\n" + students[j].toString();
}
return course + " " + numStudents + "/" + stopPoint+res;
}
//returns true if and only if the number of students in it is at stopPoint
public boolean isFull(int numStudents, int stopPoint)
{
if (numStudents == stopPoint)
{
return true;
}
else
return false;
}
/*add given student to this roster if student already on roster
or numStudents already == stopPoint, will not change roster and return
false but return true if successful, else false
*/
public boolean addStudent(Student student)
{
if(this.numStudents < this.stopPoint)
{
this.students[numStudents] = student; // here is where I get the error
this.numStudents++;
return true;
}
else
return false;
}
}
Testing Class:
public class TestRoster
{
public static void main(String[] args)
{
Student s1 = new Student("John","Doe");
Course c1 = new Course(198, 111);
Roster r1 = new Roster(4, c1);
System.out.println(r1);
testAdd(r1, s1);
}
private static void testAdd(Roster r, Student s)
{
System.out.println(s.familyName+" "+r.addStudent(s));
System.out.println(r);
}
}
Student Class:
public class Student
{
String personalName;
String familyName;
public Student(String pName, String fName)
{
personalName = pName;
familyName = fName;
}
public String toString( )
{
return "Student: " + familyName + ", "+ personalName;
}
}
Lastly, the Course Class:
public class Course
{
int deptNum;
int courseNum;
public Course(int deptNum, int courseNum)
{
this.deptNum = deptNum;
this.courseNum = courseNum;
}
public String toString( )
{
return deptNum + ":" + courseNum;
}
}
Here is the error:
Exception in thread "main" java.lang.NullPointerException
at assign4.Roster.addStudent(Roster.java:56)
at assign4.TestRoster.testAdd(TestRoster.java:17)
at assign4.TestRoster.main(TestRoster.java:13)
Java Result: 1`
The other answers suggest using an arbitrary number for the array instansiation, this is not a good idea as you never know if it will be enough.
Your Roster class knows how many students there should be (via the constructor), you should initialize the Student array with stopPoint:
Student[] students;
int numStudents;
int stopPoint;
Course course;
public Roster(int stopPoint, Course course)
{
this.stopPoint = stopPoint;
this.course = course;
this.students = new Student[this.stopPoint]
}
Since you can't touch your class variables, you can and should initialize the array within the constructor.
i have problem with printing the array after reading it. After printing, the address of memory is printed, not value of the array. What can i do for that ?
public class MyClass
{
Student St = new Student();
Student[]Array1 = new Student[10];
void AddList()
{
Scanner Scan = new Scanner(System.in);
for (int i=0; i<Array1.length & i<ArrayF1.length; i++)
{
System.out.println("Enter Student NAME Number " + (i+1) + ":");
Array1[i] = new Student();
Array1[i].setName(Scan.next());
//System.out.println("Enter Student MARK Number " + (i+1) + ":");
//St.setMark(Scan.nextFloat());
}
}
this is my print method. The result of print is like this
(studentproject.Student#1a758cb)
void PrintList()
{
for (int i=0; i<Array1.length; i++)
{
System.out.println(Array1[i]);
}
}
this is my Student Class that i have all my setter and getter method on that ... So i have 3 Class how can i work with this 3 class and in one of them get the data and in another print the Mark data and in third class print the Student Name data ... how can i do that ... i do some code but i dont know is it correct or not ... thanks for your help ...
public class Student
{
private String Name;
private float Mark;
/**
* #return the Name
*/
public String getName() {
return Name;
}
/**
* #param Name the Name to set
*/
public void setName(String Name) {
this.Name = Name;
}
/**
* #return the Mark
*/
public float getMark() {
return Mark;
}
/**
* #param Mark the Mark to set
*/
public void setMark(float Mark) {
this.Mark = Mark;
}
}
Just override the toString() method in Student class, and return the appropriate string you want to get printed when you print an instance.
It may look like: -
#Override
public String toString() {
return "Name: " + studentName;
}
Currently, the default implementation of toString() method of Object class is invoked, and what you are seeing is the format returned from that method, which is of the form - Type#hashCode
Here I've added some stuff how toString() method can be override
public class Student {
private String name;
private int id;
float mark;
public Student() {
}
public Student(String name, int id) {
this.name = name;
this.id = id;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public float getMark() {
return mark;
}
public void setMark(float mark) {
this.mark = mark;
}
#Override
public String toString() {
return "Student[ID:" + id + ",Name:" + name + ",Mark:"+mark+"]";
}
public void printStudentInfo() {
// print all the details of student
}
public static void main(String[] args) {
Student[] students = new Student[10];
Scanner scanner = new Scanner(System.in);
for (int i = 0; i < students.length; i++) {
System.out.println("Enter Student Name " + (i + 1) + ":");
String name = scanner.nextLine();
Student student = new Student(name, i + 1);
System.out.println("Enter Student MARK Number " + (i + 1) + ":");
float mark = scanner.nextFloat();
student.setMark(mark);
students[i]=student;
}
for(Student student:students) {
// by default toStirng method is called
System.out.println(student);
//or you can call like
//student.printStudentInfo();
}
}
}
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");
}
}
}