Develop Reference

Referencing the array variables in the Reference class, sorting it using another method, and invoking the sorted values in the case statement

I am trying to call the array variables in the reference class, try to sort them using a user-defined method and call the method onto the case statement that will be invoked if the user chooses a particular number. I wanted to provide the user the option what attribute of a student will be sorted (i.e. name, course...) and show the sorted one dimensional array called in the case statements and invoked through the main method.
Here's the variables in the Reference class:
class RecordReference {
private int idNumber;
private String firstName = "";
private String middleName = "";
private String lastName = "";
private int age;
private String yearLevel;
private String course = "";
private double gwa;
public RecordReference(int i, String f, String m, String l, int a, String y, String c, double g) {
idNumber = i;
firstName = f;
middleName = m;
lastName = l;
age = a;
yearLevel = y;
course = c;
gwa = g;
}
public int getIdNumber() {
return idNumber;
}
public String getFirstName() {
return firstName;
}
public String getMiddleName() {
return middleName;
}
public String getLastName() {
return lastName;
}
public int getAge() {
return age;
}
public String getYearLevel() {
return yearLevel;
}
public String getCourse() {
return course;
}
public double getGwa() {
return gwa;
}
public void setIdNumber(int idnumber) {
idNumber = idnumber;
}
public void setFirstName(String fName) {
firstName = fName;
}
public void setMiddleName(String mName) {
middleName= mName;
}
public void setLastNameName(String lName) {
lastName= lName;
}
public void setAge(int a) {
age = a;
}
public void setYearLevel(String yLevel) {
yearLevel = yLevel;
}
public void setCourse(String c) {
course = c;
}
public void setGwa(int gwa) {
gwa = gwa;
}
public String toString() {
return String.valueOf(System.out.printf("%-15s%-15s%-15d%-15d%n",
firstName, course , yearLevel ,gwa));
}
} // end of class
And I am trying to call it in this sort method, but I don't know how to reference it.
public static void sortFirstNameArray(String[] f){
for (int i = 0; i < f.length - 1; i++) {
for (int j = i + 1; j < f.length; j++) {
if (f[i].compareToIgnoreCase(f[j]) > 0) {
String temp = f[i];
f[i] = f[j];
f[j] = temp;
}
}
}
}
After the sorting is successfully done, I'll call it in a switch case statements that will be invoked once the user chooses a particular number. This part has 5 case statements (Name, Age, Course, General Weighted Average and the option to sort it all - I plan to add more student attributes if this works)
(I don't know if I should store this in another method and call it in the main method or just put it in the main method like that)
public RecordReference Process(RecordReference[] f, RecordReference[] a) {
// for loop?
for (int x = 0; x < f.length; x++) {
switch (choice) {
case 1:
System.out.println("Sorted array of first name: ");
sortFirstNameArray(f[x].getFirstName());
System.out.printf("%-15s%n", Arrays.toString(f));
break;
case 2:
System.out.println("Sorted array of age: ");
// invokes the age method
sortAgeArray(a[x].getAge());
System.out.printf("%-15s%n", Arrays.toString(a));
break;
}
}
}
If it is in another method, what param do I include when I call it in the main method?
I tried this but it doesn't work, I don't know what to do
System.out.print("Please choose what student attribute you want to
sort :");
choice = keyboard.nextInt();
// calling the process method here, but I receive syntax error
Process(f,a); // Here, I want to pass the sorted values back into the array but I get an error.
If you can help me out that would be great. Thank you in advance.
I'm just a first year student and I am eager to learn in solving this error.

It's good to see that you have attempted the problem yourself and corrected your question to make it clearer, because of that I am willing to help out.
I have tried to keep the solution to the problem as close to your solution as possible, so that you are able to understand it. There may be better ways of solving this problem but that is not the focus here.
First of all, let's create a class named BubbleSorter that will hold methods for sorting:
public class BubbleSorter
{
//Explicitly provide an empty constructor for good practice.
public BubbleSorter(){}
//Method that accepts a variable of type RecordReference[], sorts the
//Array based on the firstName variable within each RecordReference
//and returns a sorted RecordReference[].
public RecordReference[] SortByFirstName(RecordReference[] recordReferencesList)
{
for (int i = 0; i < recordReferencesList.length - 1; i++) {
for (int j = i + 1; j < recordReferencesList.length; j++) {
if (recordReferencesList[i].getFirstName().compareToIgnoreCase
(recordReferencesList[j].getFirstName()) > 0) {
RecordReference temp = recordReferencesList[i];
recordReferencesList[i] = recordReferencesList[j];
recordReferencesList[j] = temp;
}
}
}
return recordReferencesList;
}
}
That gives us a class that we can instantiate, where methods can be added to be used for sorting. I have added one of those methods which takes a RecordReference[] as a parameter and sorts the RecordReference[] based on the firstName class variable within each RecordReference. You will need to add more of your own methods for sorting other class variables.
Now for the main class:
class Main {
public static void main(String[] args) {
//Get a mock array from the GetMockArray() function.
RecordReference[] refArray = GetMockArray();
//Instantiate an instance of BubbleSorter.
BubbleSorter sorter = new BubbleSorter();
//Invoke the SortByFirstName method contained within the BubbleSorter
//and store the sorted array in a variable of type RecordReference[] named
//sortedResult.
RecordReference[] sortedResult = sorter.SortByFirstName(refArray);
//Print out the results in the sorted array to check if they are in the correct
//order.
//This for loop is not required and is just so that we can see within the
//console what order the objects in the sortedResult are in.
for(int i = 0; i < sortedResult.length; i++)
{
System.out.println(sortedResult[i].getFirstName());
}
}
public static RecordReference[] GetMockArray()
{
//Instantiate a few RecordReferences with a different parameter for
//the firstName in each reference.
RecordReference ref1 = new RecordReference(0, "Ada", "Test", "Test", 22, "First",
"Computer Science", 1.0f);
RecordReference ref2 = new RecordReference(0, "Bob", "Test", "Test", 22, "First",
"Computer Science", 1.0f);
RecordReference ref3 = new RecordReference(0, "David", "Test", "Test", 22,
"First", "Computer Science", 1.0f);
//Create a variable of type RecordReference[] and add the RecordReferences
//Instantiated above in the wrong order alphabetically (Based on their firstName)
//class variables.
RecordReference[] refArray = {
ref2, ref3, ref1
};
return refArray;
}
}
In the main class I have provided verbose comments to explain exactly what is happening. One thing I would like to point out is that I have added a method named GetMockArray(). This is just in place to provide a RecordReference[] for testing and you probably want to do that somewhere else of your choosing.
If anything is not clear or you need some more assistance then just comment on this answer and I will try to help you further.
Thanks.

Java cycling through objects

I'm trying to cycle through objects and update a variable each time, I have a Player class that has all of the following variables:
Name, s1 ,s2, s3,...., s11, total
I want to go through each variable from the start to the end and adding the score at each go for each player (all the players are in an array list).
I'm not sure what the best way to do this is, is there a way to select a specific object and then add the variable depending on who go it is.
if you need any more information please ask and thanks in advance for any help given.
public void addScore(int turn, int score){
Player.setScore( turn, score);
}

You can cycle in array list with a simple for, like this:
ArrayList<Player> players = ...;
for (int i = 0; i < players.size(); i++) {
/*Operations on players[i] = the current player*/
}
To take and modify the variables of your player you can create getter and setter methods for each parameter like this:
private String name;
public String getName(){
return name;
}
public void setName(String name){
this.name = name;
}
If you have a lot of variables (s1, s11) of the same type, use an array:
int[] scores = new int[11];
So you can use another for cycle.

If I understand this question correctly, each player has a name, 11 scores, and a total. You seem to be asking how to iterate through a list of players and make the total equal to the sum of the 11 scores.
A more usual (in an OO language) approach would be just to ensure that the total is always equal to the sum of the 11 scores. (This is called "encapsulation", and is the fundamental idea behind all of object-oriented programming.) This is very easy to accomplish (for ease of programming, I put the scores in an array):
public class Player {
private String name ;
private int[] scores ;
private int total ;
public Player(String name) {
this.name = name ;
this.scores = new int[11] ; // all initialized to zero, as is total.
}
public void setScore(int whichScore, int score) {
int change = score - scores[whichScore] ;
scores[whichScore] = score ;
total = total + change ;
}
public int getScore(int whichScore) {
return scores[whichScore] ;
}
public int getTotal() {
return total ;
}
public String getName() {
return name ;
}
public void setName(String name) {
this.name = name ;
}
}
Now your question is redundant: the total is always equal to the sum of the scores, so there is no need to iterate through the players to compute the total anywhere in your code. You can get the total for each player with
for (Player p : listOfPlayers) {
System.out.println("Player "+p.getName()+" has total score "+p.getTotal());
}

Inputting random integers into a file and sorting them into another file? FileIO

I'm trying to create a FileIO where random numbers are placed into a .txt file and outputted, sorted in another .txt file. I have a bubble sort code that can sort numbers & I have another code that makes a .txt file. I'm just not sure how I'd implement these 2 together.
Here's my fileIO code:
public static void main(String[] args) {
File file = new File("test.txt");
//Writes name and age to the file
try {
PrintWriter output = new PrintWriter(file);
output.println("Rober");
output.println(27);
output.close();
} catch (IOException ex) {
System.out.printf("ERROR: %s\n", ex);
}
//Reads from the file
try {
Scanner input = new Scanner(file);
String name = input.nextLine();
int age = input.nextInt();
System.out.printf("Name: %s Age %d\n", name, age);
} catch (FileNotFoundException ex) {
System.out.printf("ERROR: %s\n", ex);
}
}
And here is my bubble sort code:
public static void main(String[] args) {
Random num = new Random();
//Creating an array for 10 integers
int [] number = new int [10];
System.out.print("Random Numbers:");
/*Display the unsorted numbers in a random order.
These numbers range from 0 to 100
*/
for (int d = 0 ; d<number.length ; d++){
/* We add a "+1" to the nextInt(100) here because then the numbers
will only range from 0 to 99.
*/
int RandomG = num.nextInt(100)+1;
number[d] = RandomG;
System.out.print(" " +RandomG);
}
//Display the sorted numbers
System.out.print("\nSorted Numbers:"+Arrays.toString(BubbleSortAsceMethod(number)));
}
public static int [] BubbleSortAsceMethod(int[] number){
int placeholder;
for(int i = 0 ; i < number.length-1 ; i++){
for ( int x = 1 ; x < number.length-i ; x++){
/*If the first number in the sequence is greater than the second
number, than save the first number of sequence in placeholder
and place the second number in the first numbers position, and
put the placeholder in the second numbers position (SWAP).
*/
/*
Since this is saying that when the first term is bigger than the
2nd term, the sequence will increase. If we flip the relational
operator, the sequence will decrease.
*/
if ( number[x-1] < number[x]){
placeholder = number[x-1];
number[x-1] = number[x];
number[x] = placeholder;
}
}
}
return number;
}
I'm kinda new to all this java stuff so please go a bit easy on me! Any help at all is appreciated :)

As the data contained in the file will consist of a pair of values: The name (String) and the age (int), you will need to retain their relationship. The best way of doing this would be to create a Class to represent the data. Eventually you want to sort the data on age using your BubbleSort method. While practically this would not be your first choice to sort data, I assume that this is a requirement. The BubbleSort method you have sorts an int[] by comparing each entry against it's immediate neighbor. With int being primitive, you can directly compare each element using the < operator.
public class Person implements Comparable<Person> {
private String name;
private int age;
public Person(String name, int age) {
this.age = age;
this.name = name;
}
public String getName() { return name; }
public int getAge() { return age; }
#Override
public String toString() {
return name + System.lineSeperator() + age;
}
#Override
public int compareTo(Person person) {
return this.age - person.age;
}
}
You may want to implement the Comparable interface to compare Objects; in which the interface must be implemented by Overriding the compareTo(Person person) method. You can impose sorting on age by returning the difference in age. This is not the only way you can impose the order you want; you may wish to compare directly using the getAge() of each Object or create a Comparator object.
Using the Comparable interface does allow you to make your BubbleSort class more generic, however (though the array must be of Objects that implement the interface; hence no primitive types).
public class BubbleSort {
public static <T extends Comparable> T[] BubbleSortAsceMethod(T[] array) {
for (int i = 0; i < array.length - 1; i++) {
for (int x = 1; x < array.length - i; x++) {
if (comparator.compare(array[x - 1], array[x]) < 0) {
T placeholder = array[x - 1];
array[x - 1] = array[x];
array[x] = placeholder;
}
}
}
return array;
}
}
You will notice that this sort method has some slight differences from your original, namely the BubbleSortAsceMethod method signature with the introduction of generic type parameters. Once again, this is completely optional, though this does give you the flexibility to use this method in the future for other arrays of Classes that extend the Comparable interface.
If you don't want to use generics or the Comparable interface, you will need to change the method signature and if statement.
You're method signature should instead look like public static Person[] BubbleSortAsceMethod(Person[] array) and the if statement if (array[x-1].getAge() < array[x].getAge())
This can give you an illustration of it working, though this does not consider the file io which should be simple to implement from what you have done already.
static Random random = new Random();
public static void main (String args[]) {
int size = 100;
Person[] peopleArray = new Person[size];
for (int i = 0; i < size; i++) {
String name = generateName(random.nextInt(4) + 4);
int age = random.nextInt(100);
peopleArray[i] = new Person(name, age);
}
peopleArray = BubbleSort.BubbleSortAsceMethod(peopleArray);
}
Note that this conforms, at least as much as possible, to the code you have implemented this far. If the BubbleSort and use of arrays are not critical, data structures that implement the List interface, such as ArrayList, can allow you to implement this much cleaner. This does not use the BubbleSort method at all.
public static void main (String args[]) {
int size = 100;
ArrayList<Person> people = new ArrayList<>();
for (int i = 0; i < size; i++) {
String name = generateName(random.nextInt(4) + 4);
int age = random.nextInt(100);
people.add(new Person(name, age));
}
peopleList.sort(Person::compareTo);
//or, if you don't want to implement comparable
peopleList.sort(Comparator.comparing(Person::getAge));
}
Appendix:
Used for illustrative purposes: Generates a name of a set length (randomly).
static char[] alphabet = "abcdefghijklmnopqrstuvwxyz".toCharArray();
public static String generateName(int length) {
if (length > 0) {
return alphabet[random.nextInt(alphabet.length)] + generateName(length - 1);
}
return "";
}

Array project seems to only print out null

The program is supposed to assign random values to the Student objects in the studentArr array.
Right now it is only printing out null values. Ive tried several different print methods.
I'm pretty sure its something wrong with either my method that is supposed to fill out each student object's attributes, or with my print statement.
import java.util.*;
public class Lab6Excercise
{
String[] first={"Rick","Morty","Moriarty","Samus","Promethius","Geiger","Moriarti","Bob","Taco",
"Asparagus","Shoes","Potato","Dirty","Dan","Spongebob","Space","Nova","Illadin","Orange","Electron"};
String[] last={"PoopyButthole","Red","Mantis","Toboggan","Oak","Elm","Dumbledore","Potter","Spice","Toothbrush","Argon",
"Blitz","LazerWolf","Mc-BigMac","King","Queen","Spork","Petrolium","Apple","Trash"};
//no syntax errors if set to static, but prints out null for everything.
//problem here or in calling array to print?
public static Student[] studentArr= new Student[20];
public Lab6Excercise(){
initializeArray();
}
public void initializeArray(){
for(int i=0; i>20; i++){
//this one seems correct but it cant find the symbol method- setStudentID etc. methods
// online it said to try (Student)studentArr.setStudentID(id())
//which explicitely casts it
//seems to work
//http://stackoverflow.com/questions/29328569/setting-values-to-an-array-of-objects
studentArr[i]= new Student();
studentArr[i].setStudentID(id());
studentArr[i].setFirstName(First());
studentArr[i].setLastName(Last());
studentArr[i].setGrade(Grades());
//other way?probably wrong
//studentArr[i]= new Student(studentArr.id(),
//studentArr.First(),
//studentArr.Last(),
//studentArr.Grades());
}
}
public Student[] getStudentArr(){
return studentArr;
}
//do i even need this?
//public Lab6Excercise getLab(){
// return lab;
//}
public static void main(String[] args){
//randomly generate double grade, student id;
//create 2 arrays, first name, last name. pull randomly for name generation
//necessary? how do i
Lab6Excercise lab= new Lab6Excercise();
//prints out hash or something
//System.out.println(lab.studentArr.toString());
//prints out nulls
// System.out.println(Arrays.deepToString(studentArr));
for(int i=0; i<studentArr.length; i++){
System.out.println(studentArr[i]);
}
}
public int id(){
int ID=1+(int)(Math.random()*((100-1)+1));
return ID;
}
public String First(){
Random random= new Random();
int index= random.nextInt(first.length);
return first[index];
}
public String Last(){
Random random= new Random();
int index= random.nextInt(last.length);
return last[index];
}
public double Grades(){
double grade=0+(double)(Math.random()*((4-1)+1));
return grade;
}
}
and the object class
import java.util.Random;
public class Student
{
private int studentID;
private String firstName;
private String lastName;
private double grade;
// no-argument constructor calls other constructor with default values
public Student()
{
this( 0, "", "", 0.0 ); // call four-argument constructor
} // end no-argument Student constructor
// initialize a record
public Student( int id, String first, String last, double grade )
{
setStudentID( id );
setFirstName( first );
setLastName( last );
setGrade( grade );
} // end four-argument Student constructor
// set student ID number
public void setStudentID( int id )
{
studentID = id;
} // end method setStudentID
// get student ID number
public int getStudentID()
{
return studentID;
} // end method getStudentID
// set first name
public void setFirstName( String first )
{
firstName = first;
} // end method setFirstName
// get first name
public String getFirstName()
{
return firstName;
} // end method getFirstName
// set last name
public void setLastName( String last )
{
lastName = last;
} // end method setLastName
// get last name
public String getLastName()
{
return lastName;
} // end method getLastName
// set grade
public void setGrade( double gradeValue )
{
grade = gradeValue;
} // end method setGrade
// get grade
public double getGrade()
{
return grade;
} // end method getGrade
public static int getRandom(int[] array){
int rnd= new Random().nextInt(array.length);
return array[rnd];
}
public String toString(){
return "First name: "+firstName + "Last name: " + lastName+ "ID: "+ studentID+ "Grade: " + grade+"\n";
}
}

You never initialize your array, because your for loop indexing is wrong.
for (int i = 0; i > 20; i++)
This says: for i starting at 0, run the following code if i is greater than 20, incrementing the value of i by 1 each time. Since i starts out already being less than 20, it is never greater than 20, and the code never runs. Instead, do the following, making your run-condition i less than 20:
for (int i = 0; i < 20; i++)
Or, better yet:
for (int i = 0; i < studentArr.length; i++)
For more details on the syntax of the for statement, check out the Java documentation.

It's a simple error in your for loop in the initialize array method. The statement: i >20 is the condition under which the loop will execute. But if i starts as 0 it will never be 20 and the loop will never execute. Just change the condition (which is i >20 right now) to i < 20 and it will work. :)

How to change the position within the array

I have one class which is called people where I keep track of 50 people, their rank, name, age and order. Then I have a second class called rearrange where I have to change the position of the int order. So it will change up the order, like order 1 which is in position 0, will be moved to position 48th. I need to do the whole thing without using any loop.
class people {
int order[] = new int[50];
for(int j=0; j<order.length; j++) {
order[j] = "order" + j;
System.out.print(order);
}
}
class rearrange {
// In here i need to change the position of the int order, and need to do this without using any loop.
}

Shouldn't rearrange be a method of the people class? Classes are usually created for Nouns, Verbs are usually functions or methods of a class. And wouldn't it be better to have a class "Person" and make an array of 50 of them, and simply change their index to change their order?
Consider something like this:
public class Person //create Person class with the attributes you listed
{
private int rank;
private int age;
private String name;
public Person(int rank, int age, String name) //constructor
{
this.rank = rank;
this.age = age;
this.name = name;
}
}
public class MainClass
{
Person[] people = new Person[50]; //array of Persons, containing 50 elements
public static void main(String[] args)
{
for(int i = 0; i < people.length(); i++)
{
people[i] = new Person(something, something, something); //give all the people some values, you'll have to decide what values you are giving them
}
//do something with the rearrange function here
}
public static void rearrange(int target, int destination) //this is just a "swap" function
{
Person temp = people[destination];
people[destination] = people[target];
people[target] = temp;
}
}