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;
}
Related
public class pro1{
static ArrayList <String> student = new ArrayList<String>();
static ArrayList <Integer> id = new ArrayList<Integer>();
String name;
int ID;
public pro1() {
this.name = "";
this.ID = 0;
}
public pro1(String name, int ID) {
this.name = name;
this.ID = ID;
}
public boolean addStudent(String name, int ID) {
student.add(name);
id.add(ID);
return true;
}
/*#Override
public String toString() {
return name + ID;
}*/
public static void main(String args[]) {
pro1 stu = new pro1();
stu.addStudent("john", 1);
stu.addStudent("johnny", 2);
System.out.println(stu);
}
}
I want to print out both the name of the student and the student id using ArrayList. however, I'm not sure how to do that since in this class I can only print out the ArrayList of names or the ArrayList of id. I'm thinking of maybe using another class to create a student object, but I'm not sure how to do so.
great question, I think the best solution for this would be to create a Student object just like you thought!
public static class Student {
private final String name;
private final int id;
public Student(String name, int id) {
this.name = name;
this.id = id;
}
#Override
public String toString() {
return String.format("name=%s, id=%s", name, id);
}
}
public static class School {
private final List<Student> students;
public School(List<Student> students) {
this.students = students;
}
public void add(Student student) {
students.add(student);
}
public List<Student> getStudents() {
return students;
}
}
public static void main(String... args) {
School school = new School(new ArrayList<>());
school.add(new Student("jason", 1));
school.add(new Student("jonny", 2));
school.getStudents().forEach(System.out::println);
}
Non-OOP
Loop the pair of lists.
First sanity-check: Are the two lists the same size?
if( students.size() != ids.size() ) { … Houston, we have a problem }
Then loop. Use one index number to pull from both lists.
for( int index = 0 ;
index < students.size() ;
index ++
)
{
System.out.println(
students.get( index ) +
" | " +
ids.get( index )
) ;
}
OOP
The object-oriented approach would be to define a class. The class would have two member fields, the name and the id of the particular student.
Then create a method that outputs a String with your desired output.
All this has been covered many times on Stack Overflow. So search to learn more. For example: Creating simple Student class and How to override toString() properly in Java?
Uncomment and modify your toString() method as below. It will print both student and id.
#Override
public String toString() {
return student.toString() + id.toString();
}
If you want to have Student to Id mapping, best is to have them in Map collection. Id as key and student name as value.
I want to add values to the objects with out looping because if there are 1000 of objects then I don't want to loop all of them.I want to add age randomly to the students based on the Name of the student.Is there are any way to add values
Here is the code
import java.util.*;
import java.io.*;
class Student{
Student(String Name){
this.Name=Name;
}
String Name;
int age;
}
public class HelloWorld{
public static void main(String []args){
String a []={"Ram","Krishna","Sam","Tom"};
ArrayList<Student> al = new ArrayList<Student>();
for(int i=0;i<a.length;i++){
Student c;
c=new Student(a[i]);
al.add(c);
}
for(Student obj:al){
if(obj.Name.equals("Krishna")){
obj.age=24;
}
System.out.println("Name = "+ obj.Name + " Age = " + obj.age);
}
}
}
First some minor points:
You should never use the fields directly but create getter and setters instead. The fields should be private. Variable names should start with a lower case letter by convention. So this would be the adjusted Student class:
public class Student {
private String name;
private int age;
public Student(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
To store the Student objects you can use a map with names as keys and Student instances as values.
It is good practice to declare the variable only with the interface type Map and not with the concrete implementation HashMap. A hash map has O(1) complexity for searching by key. So you don't need a loop to iterate through all Student instances. (The HashMap.get() implementation doesn't use a loop internally.)
public static void main(String[] args) {
String a [] = {"Ram", "Krishna", "Sam", "Tom"};
// Keys: student names
Map<String, Student> al = new HashMap<String, Student>();
// Fill the Student's map
for(int i = 0; i < a.length; i++){
String name = a[i];
al.put(name, new Student(name));
}
// Manipulate one student by name. If there is no entry for that name we get null.
// So we better check for null before using it.
Student student = al.get("Krishna");
if(student != null) {
student.setAge(24);
}
// Output the all students
for(Student obj: al.values()){
System.out.println("Name = "+ obj.getName() + " Age = " + obj.getAge());
}
}
My code is as follows:
import java.io.*;
import java.util.*;
public class readStudents extends Object
{
private String SName = "";
private String DoB = "";
private String Gender = "";
private String Address = "";
Student [] students = new Student[20];
public void fillStudentArray()
{
// properties
int size; // total number of Students in collection
File file = new File("StudentDetails.txt");
try
{
Scanner in = new Scanner(file);
while(in.hasNextLine())
{
String SName = in.next();
String DoB = in.next();
String Gender = in.next();
String Address = in.next();
}
}
catch (FileNotFoundException e)
{
e.printStackTrace();
}
}
public String getName()
{
return this.SName;
}
public void printname()
{
System.out.println("hello");
}
public Student search(String name)
{
System.out.print("Enter the name you wish to search: ");
for (int i = 0; i < this.students.length; i++)
{
Student s = this.students[i];
if (s.getName().equalsIgnoreCase(name))
{
return s;
}
}
return null;
}
} //end class students
However I am trying to create a well refined program that I can call on these methods from another main file with as minimal code as possible in that file.
The search method at the bottom is tripping me up as I am assuming I need to put something to do with the array in my getName() method but I can't figure it out.
Since I am doing this as a class for another main method, with the placement of my array initialization and declaration it allows the other methods to access it but it leaves me with no way to create this array from the main method unless I am missing something?
This is the error jCreator is throwing:
F:\University\Ass2\readStudents.java:62: error: cannot find symbol
if (s.getName().equalsIgnoreCase(name))
^
symbol: method getName()
location: variable s of type Student
You never populated the Student students[] array... You retrieved the values you would populate them with here:
while(in.hasNextLine())
{
String SName = in.next();
String DoB = in.next();
String Gender = in.next();
String Address = in.next();
}
But you never actually set those values into a Student object in the students[] array
Do something like this:
int i = 0;
while(in.hasNextLine())
{
String name = in.next();
String dateOfBirth = in.next();
String gender = in.next();
String address = in.next();
students[i] = new Student(name, dateOfBirth, gender, address);
i++
}
Also, you might consider ditching the array and using some sort of List or Hash object... If your file contains more than 20 lines, the array will be out of index when you try to define the 21st value.. With an arraylist or a List you wouldn't have that problem
I took a liberty to tweak your code as previous answer mentioned, it's better to use array list in your case. You could make a small student container class within your reader. The get name method is also kinda redundant ;s
package test;
import java.io.*;
import java.util.*;
public class readStudents{
ArrayList<Student> students = new ArrayList<Student>();
class Student {
private String name;
private String dob;
private String gender;
private String address;
public Student(String name, String dob, String gender, String address) {
this.name = name;
this.dob = dob;
this.gender = gender;
this.address = address;
}
public void fillStudentArray() {
// properties
int size; // total number of Students in collection
File file = new File("StudentDetails.txt");
try {
Scanner in = new Scanner(file);
while (in.hasNextLine()) {
String SName = in.next();
String DoB = in.next();
String Gender = in.next();
String Address = in.next();
students.add(new Student(SName, DoB, Gender, Address));
}
}
catch (FileNotFoundException e) {
e.printStackTrace();
}
}
public String getName(Student student) {
return student.name;
}
public void printname() {
System.out.println("hello");
}
public Student search(String name) {
System.out.print("Enter the name you wish to search: ");
for (Student student : students) {
if (student.name.equalsIgnoreCase(name))
;
return student;
}
return null;
}
}
}
If you're not forced by your teacher to use for or for-each cycle in the search function - this is how to do a full scan the Java 8 way
public Optional<Student> findFirstByName(final String name) {
return Arrays.stream(students)
.filter(s -> s.getName().equalsIgnoreCase(name))
.findFirst();
}
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)
}
Let say I have an ArrayList<Student> contains 4 Students(name , city, school).
For example:
1. John Nevada BBBB
2. Mary Ander AAAA
3. Winn Arcata CCCC
4. Ty Artes BBBB
If user enter “BBBB” then it displays: :
1. John Nevada BBBB
2. Ty Artes BBBB
My question is that how do I compare a input string “BBBB” with the schools in the above ArrayList?
Thank you for any help that you guys would provide!
public class Student
{
private String name;
private String city;
private String school;
/**
* Constructor for objects of class Student
*/
public Student(String name, String city, String school)
{
this.name = name;
this.city = city;
this.school = school;
}
public String getSchool(String school)
{
return this.school = school;
}
public String toString()
{
return "Name: " + name + "\tCity: " +city+ "\tSchool: "+school;
}
}
public class AllStudent
{
// instance variables - replace the example below with your own
private ArrayList<Student> listStudent = new ArrayList<Student>();
/**
* Constructor for objects of class AllStudent
*/
public AllStudent() throws IOException
{
//variables
// read an input file and save it as an Arraylist
fileScan = new Scanner (new File("students.txt");
while(fileScan.hasNext())
{
//.......
listStudent.add(new Student(name,city,school);
}
//now let user enter a school, the display name, city, school of that student.
//i am expecting something like below...
public void displayStudentBasedOnSchool(String school)
{
for (i = 0; i < listStudent.size(); i++)
{
//what should i put i here to comapre in input School with school in the listStudent>
}
}
}
Assuming your student is modelled like this (AAAA, BBBB values are stored in blah field):
public class Student {
private String name;
private String state;
private String blah;
//getters & setters..
}
The simplest (not most efficient way) is just to loop the array list and compare the query string with value of blah field
for(Student s : studentList) {
if(s.getBlah().equals(queryString)) {
// match!..
}
}
I believe Student is class and you are creating list of Student
The ArrayList uses the equals method implemented in the class (your case Student class) to do the equals comparison.
You can call contains methods of list to get matching object
Like,
public class Student {
private String name;
private String city;
private String school;
....
public Student(String name, String city, String school) {
this.name = name;
this.city = city;
this.school = school;
}
//getters & setters..
public String setSchool(String school) {
this.school = school;
}
public String getSchool() {
return this.school;
}
public boolean equals(Object other) {
if (other == null) return false;
if (other == this) return true;
if (!(other instanceof Student)) return false;
Student s = (Student)other;
if (s.getSchool().equals(this.getSchool())) {
return true; // here you compare school name
}
return false;
}
public String toString() {
return "Name: " + this.name + "\tCity: " + this.city + "\tSchool: "+ this.school;
}
}
Your array list would be like this
ArrayList<Student> studentList = new ArrayList<Student>();
Student s1 = new Student(x, y, z);
Student s2 = new Student(a, b, c);
studentList.add(s1);
studentList.add(s2);
Student s3 = new Student(x, y, z); //object to search
if(studentList.contains(s3)) {
System.out.println(s3.toString()); //print object if object exists;
} // check if `studentList` contains `student3` with city `y`.It will internally call your equals method to compare items in list.
Or,
You can simply iterate object in studentList and compare items
for(Student s : studentList) {
if(s.getSchool().equals(schoolToSearch)) {
// print object here!..
}
}
Or, as you commented ,
public void displayStudentBasedOnSchool(String school){
for(int i = 0; i < studentList.size(); ++i) {
if(studentList.get(i).getSchool().equals(school)) {
System.out.println(studentList.get(i).toString()); // here studentList.get(i) returns Student Object.
}
}
}
Or,
ListIterator<Student> listIterator = studentList.listIterator(); //use list Iterator
while(listIterator.hasNext()) {
if(iterator.next().getSchool().equals(school)) {
System.out.println(listIterator.next());
break;
}
}
or even,
int j = 0;
while (studentList.size() > j) {
if(studentList.get(j).getSchool().equals(school)){
System.out.println(studentList.get(j));
break;
}
j++;
}
So now you have set of options
for-loop
for-each loop
while loop
iterator
I would probably use Guava library from Google.
Take a look at this question: What is the best way to filter a Java Collection? It provides many excelent solutions for your problem.