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.

Object won't construct due to int error even tho they're included in the class [duplicate]

This question already has answers here:
Java error: constructor in class cannot be applied to given types
(3 answers)
Closed 4 years ago.
I have a three classes, one to demo and another to extend the first. Everything compiles when in the demo is gives me this error:
EssayDemo.java:11: error: constructor Essay in class Essay cannot be applied to given types;
Essay termPaper = new Essay();
^
required: int,int,int,int
The four ints are Grammar, Spelling, Length, and Content. I set them up but they don't construct an object properly.
This might have been easier if it weren't for the fact that I have to use two classes that I didn't write. Here are the two specific pieces of code. Here's the essayDemo.java:
/**
This program demonstrates a solution to
the Essay Class programming challenge.
*/
public class EssayDemo
{
public static void main(String[] args)
{
// Create an Essay object.
Essay termPaper = new Essay();
// Assign scores to the object.
// Grammer = 25 points, Spelling = 18 points,
// Length = 20 points, and Content = 25 points.
termPaper.setScore(25.0, 18.0, 20.0, 25.0);
// Display the score details.
System.out.println("Term paper:");
System.out.println("Grammar points: " + termPaper.getGrammar());
System.out.println("Spelling points: " + termPaper.getSpelling());
System.out.println("Length points: " + termPaper.getCorrectLength());
System.out.println("Content points: " + termPaper.getContent());
System.out.println("Total points: " + termPaper.getScore());
System.out.println("Grade: " + termPaper.getGrade());
}
}
And here's the gradedActivity.java:
/**
The GradedActivity class stores data about a graded
activity for the Essay Class programming challenge.
*/
public class GradedActivity
{
private double score; // Numeric score
/**
The setScore method sets the score field.
#param s The value to store in score.
*/
public void setScore(double s)
{
score = s;
}
/**
The getScore method returns the score.
#return The value stored in the score field.
*/
public double getScore()
{
return score;
}
/**
The getGrade method returns a letter grade
determined from the score field.
#return The letter grade.
*/
public char getGrade()
{
char letterGrade;
if (score >= 90)
letterGrade = 'A';
else if (score >= 80)
letterGrade = 'B';
else if (score >= 70)
letterGrade = 'C';
else if (score >= 60)
letterGrade = 'D';
else
letterGrade = 'F';
return letterGrade;
}
}
Here's the code I've written to extend it:
public class Essay extends GradedActivity
{
private final int grammarPossible = 30;
private final int spellingPossible = 20;
private final int lengthPossible = 20;
private final int contentPossible = 30;
private final int overallPossible = 100;
private int grammarGrade;
private int spellingGrade;
private int lengthGrade;
private int contentGrade;
private int overallGrade;
public Essay(int grammar, int spelling, int length, int content){
setGrammarGrade(grammar);
setSpellingGrade(spelling);
setLengthGrade(length);
setContentGrade(content);
setOverallGrade();
setScore(getOverallGrade());
}
public int getGrammarGrade(){
return grammarGrade;
}
public void setGrammarGrade(int grammarGrade){
this.grammarGrade = grammarGrade;
}
public int getSpellingGrade(){
return spellingGrade;
}
public void setSpellingGrade(int spellingGrade){
this.spellingGrade = spellingGrade;
}
public int getLengthGrade(){
return lengthGrade;
}
public void setLengthGrade(int lengthGrade){
this.lengthGrade = lengthGrade;
}
public int getContentGrade(){
return contentGrade;
}
public void setContentGrade(int contentGrade){
this.contentGrade = contentGrade;
}
public int getOverallGrade(){
return overallGrade;
}
public void setOverallGrade(){
int grades = grammarGrade + spellingGrade + lengthGrade + contentGrade;
this.overallGrade = grades;
}
public int getGrammarPossible(){
return grammarPossible;
}
public int getSpellingPossible(){
return spellingPossible;
}
public int getLengthPossible(){
return lengthPossible;
}
public int getContentPossible(){
return contentPossible;
}
public int getOverallPossible(){
return overallPossible;
}
}
I have four ints in the essay method but they aren't excepted in the constructor. Everything compiles.

required: int,int,int,int
The error is telling you that your constructor requires arguments (public Essay(int grammar, int spelling, int length, int content)). Right now you are trying to construct an Essay , but are not passing any arguments to it.
You need to provide those arguments, or provide a no args constructor:
public Essay(){}
Or if you wanted to initialize them all to zero and initialize the variables later:
Essay termPaper = new Essay(0,0,0,0);

Reading from keyboard to build a relationship between objects

I want to create an object named "Course", and get the information from the keyboard. The last attribute called the "pre", which means the prerequisite courses of this course. I want to input the whole information in one line and extract the information for each attribute. But I got the problem with"pre". I run the program and the output of course.pre is null. I do not know why. Here is my Course class code:
`import java.util.HashSet;
public class Course{
private String name;
private int isFall;
private int NumPre;
private HashSet<Course> pre;
public Course(String name) {
this.name = name;
}
public String getName() {
return name;
}
public String setName (String n){
return name = n;
}
// 1 - fall 0 - both -1 - spring
public void setType(String isFall) {
if(isFall.equals("F") || isFall.equals("f")){
this.isFall = 1;
}else if(isFall.equals("S") || isFall.equals("s")){
this.isFall = -1;
}else if(isFall.equals("B") || isFall.equals("b")){
this.isFall = 0;
}
}
public int getType(){
return isFall;
}
public void SetNumPre(int n) {
this.NumPre = n;
}
public int getNumPre() {
return NumPre;
}
public void addPre(Course c) {
pre.add(c);
}
public HashSet<Course> getPre() {
return pre;
}
}
`
And here is my main method here:
import java.util.*;
public class TimeToGraduate {
public static void main(String[] args){
Scanner scanner = new Scanner(System.in);
//System.out.print("Input first two integers here: ");
String globalInfo = scanner.nextLine();
String[] numOfCourse = globalInfo.split(" ");//[0] num of total course [1] max num per semester
int totalNum = Integer.parseInt(numOfCourse[0]);
int maxPre = Integer.parseInt(numOfCourse[1]);
Course courses[] = new Course[totalNum];
//System.out.print("Please input course list here: ");
String coursesList = scanner.nextLine();
String[] nameOfCourse = coursesList.split(" ");
for(int i = 0;i < totalNum; i++){
courses[i] = new Course(nameOfCourse[i]);
}
//System.out.print("Please input course info here: ");
for(int i = 0;i < totalNum; i++){
String courseInfo = scanner.nextLine();
String[] infoOfCourse = courseInfo.split(" ");
courses[i].setName(infoOfCourse[0]);
courses[i].setType(infoOfCourse[1]);
courses[i].SetNumPre(Integer.parseInt(infoOfCourse[2]));
if(courses[i].getNumPre() > 0){
for(int j = 3; j < 3+(courses[i].getNumPre()); j++){
for(int k = 0; k < totalNum; k++){
if(infoOfCourse[j] == courses[k].getName()){
courses[i].addPre(courses[k]);
}
}
}
}
}
scanner.close();
for(int m = 0; m < totalNum; m++){
System.out.print(courses[m].getName()+" ");
System.out.print(courses[m].getType()+" ");
System.out.print(courses[m].getNumPre()+" ");
System.out.print(courses[m].getPre()+" ");
System.out.println();
}
}
}

Notice that you did not initilize the pre attribute. That is why it is null.
It would be a good practise if you initilize the pre inside a constructor for the Course class. Otherwise, do it when you start filling the Course attributes.
Update:
Your constructor should be like this:
public Course() { this.pre = new HashSet()}
As you can see the constructor does not have any arguements, because you will be filling its attribute from the main function.
You can define a constructor with arguments too:
public Course(String name, HashSet<Course> pre)
{ this.name = name; this.pre = pre; }
But you will need to initilize pre and name when you call it from the main:
...
HashSet hs = new HashSet();
course[i] = new Course('course_name', hs);
....

Add static method to class takes array Athletes as argument and returns total nums of medals won by all

i already have the athelete class and i just dont know how to go about the rest of the problem ive been trying to do things that havent work at all but heres what i have for now. im still a beginner this is my first semester taking java so i may not understand some of the things you guys will add so if u can please explain.
This is what they are asking for me to do.
Add a static method to the class which takes an array of Athletes as its argument, and returns the total number of medals won by all athletes stored in the array. test in method.
package homework;
import java.util.Arrays;
public class Athlete {
private String name; // the name of the athlete
private String sport; // the sport the athlete does
private int numMedals; // the number of medals that the athlete has won
// constructor
public Athlete(String n, String s, int num) {
name = n;
sport = s;
numMedals = num;
}
// getters and setters for all instance variables
// (also called accessors and mutators)
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSport() {
return sport;
}
public void setSport(String sport) {
this.sport = sport;
}
public int getNumMedals() {
return numMedals;
}
public void setNumMedals(int numMedals) {
this.numMedals = numMedals;
}
/* Returns a String with information about the athlete.
*/
public String toString() {
return name + " does " + sport + " and has won " + numMedals + " medal(s).";
}
public static void AthMedals(int[][]numMedals){
for(int i = 0; i < numMedals.length;i++){
int total = 0;
for(int j = 0; j < numMedals.length; i++);
total = numMedals.getNumMedals();
}
public static void main(String[] args) {
// TODO Auto-generated method stub
Athlete SA = new Athlete("Socrates","Baseball",5);
Athlete CC = new Athlete("Cesar","Baseball",3);
Athlete JA = new Athlete("Juan","Soccer",2);
System.out.println(SA);
System.out.println(CC);
System.out.println(JA);
System.out.println("SA has " +SA.getNumMedals()+ " medals.");
}
}
}

The assignment is to write a method like
public static int sumOfAllMedals(Athlete[] all)
which returns all[0].numMedals + all[1].numMedals + ... + all[n].numMedals.
I assume AthMedals is your attempt at doing this, but it's in fact only consuming processing power while not doing anything.
I'm not gonna do your homework for you, but here's a hint:
public static int sumOfAllMedals(Athlete[] all)
{
int total = 0;
// For every Athlete in `all`, add the number of medals (s)he's won
// Should be four lines at most ;)
return total;
}

The static method have to iterate the array and add each medals to a final return variable.
static public int totalMedals(Athlete[] athelte) {
int totalMedals = 0;
for(int i=0;i<athelte.length;i++) {
totalMedals += athelte[i].numMedals;
}
return totalMeadls;
}

how to reference array from another class

To be honest i am really struggling with Java, i am trying to access an array from another class. I believe i have created the array in this code
public class aff_array {
String name;
public static void main (String[] args) {
int z = 3; //total no of affirmations
int x = 1;
aff_array[] afz = new aff_array[z]; //dim
while ( x < z ) {
afz[x] = new aff_array(); // create objects for array
x = x + 1;
}
afz[1].name = "i am the best";
afz[2].name = "you are the rest";
}
but i am really having trouble trying to figure out how i access afz[1].name for example, from another class. This is probably basic but i am really struggling..

You cannot access it from another class as long as it is created as an automatic variable (in other terms, local variable). In the above code, your "afz" construct will be visible only inside the main method (and can be used only after it's instatiation). To make it visible for other classes you can define it as an instance variable. I.e:
public class aff_array {
String name;
aff_array[] afz;
public static void main (String[] args) {
int z = 3; //total no of affirmations
int x = 1;
afz = new aff_array[z]; //dim
First, you should define it as private, and create a getter method (this is a common practice, to respect encapsulation), and then get it on the other class simply calling this method.

You can access public instance variable "name" of aff_array class
//this will print value of instance variable name
System.out.println(afz[1].name);
//If you want to modify the value of variable
afz[1].name = "modified name";
However this is not recommended. Protect your instance variable with private access modifier and access it using public getter, setter methods.
Example:
public class aff_array {
private String name;
public String getName()
{
return this.name;
}
public void setName(String new_name)
{
//You can add some validations here
this.name = new_name;
}
public static void main (String[] args) {
int z = 3; //total no of affirmations
int x = 1;
aff_array[] afz = new aff_array[z]; //dim
while ( x < z ) {
afz[x] = new aff_array(); // create objects for array
x = x + 1;
}
//To print name
System.out.println(afz[1].getName());
//to set new value to name
afz[1].setName("i am the best");
afz[2].setName("you are the rest");
}

So i have tried to add getters and it looks like this
public class aff_array {
String name;
aff_array[] afz;
public aff_array[] getAfz() {
return afz;
}
public String getName() {
return name;
}
public static void main (String[] args) {
int z = 3; //total no of affirmations
int x = 1;
aff_array[] afz = new aff_array[z]; //dim
while ( x < z ) {
afz[x] = new aff_array(); // create objects for array
x = x + 1;
}
afz[1].name = "i am the best";
afz[2].name = "you are the rest";
}
This is the other class and where i want the array value to replace aff_array.class.getName() with aff_array[] getAfz() but i dont know how to do it or reference afz(1) for example (getName is working)
public void onReceive(Context context, Intent intent)
{
setNotification(context, aff_array.class.getName());
WakeLocker.acquire(context);
Toast.makeText(context,"One shot alarm received. No more toasts will be shown.", Toast.LENGTH_SHORT).show();
WakeLocker.release();
}