I am trying to search in a list but I sort as array so that I convert my linked list to array list but when I compile it without this part below. Command prompt gives "Person is not abstract and does not override abstract method compareTo(Person) in Comparable".
How can I fix this?
public int compareTo(Person other){
if (!this.name.equalsIgnoreCase(other.name))
return this.name.compareTo(other.name);
return this.name + " "+other.name;
}
Search list and sort methods:
public void searchList(String search)
{
if(phoneList.size() == 0){
System.out.println("There is no record phone book.");
}
Node<Person> tempNode = phoneList.head;
SLinkedList<Person> tempList = new SLinkedList();
for(int i=1; i<=phoneList.size; i++)
{
if (tempNode.getElement().getName().contains(search) || tempNode.getElement().getSurname().contains(search) || tempNode.getElement().getAddress().contains(search) || tempNode.getElement().getCell().contains(search) || tempNode.getElement().getHome().contains(search) || tempNode.getElement().getWork().contains(search))
{
tempList.addLast(tempNode.getElement());
personArray = new Person[tempList.size()];
Iterator<Person> it = tempList.iterator();
while(it.hasNext()){
int x = 0;
personArray[x] = it.next();
x++;
}
bubbleSort(personArray );
for(int x = 0; x < tempList.size(); x++)
System.out.println((x+1) + ""+ personArray[x]);
}
tempNode = tempNode.getNext();
}
}
public <AnyType extends Comparable<? super AnyType>> void bubbleSort(AnyType[] a) {
int outer, inner;
for (outer = a.length - 1; outer > 0; outer--) { // counting down
for (inner = 0; inner < outer; inner++) { // bubbling up
if (a[inner].compareTo(a[inner + 1]) > 0) { // if out of order...
//then swap
swapReferences(a,inner,inner+1);
}
}
}
}
public <AnyType> void swapReferences( AnyType [ ] a, int index1, int index2 )
{
AnyType tmp = a[ index1 ];
a[ index1 ] = a[ index2 ];
a[ index2 ] = tmp;
}
Person Class:
public class Person implements Comparable<Person>
{
private String name;
private String surname;
public String address;
public String cell;
public String home;
public String work;
public Person(String name, String surname, String address, String cell, String home, String work)
{
this.name = name;
this.surname = surname;
this.address = address;
this.cell = cell;
this.home = home;
this.work = work;
}
// Accessor methods:
public String getName(){
return name;
}
public String getSurname(){
return surname;
}
public String getAddress(){
return address;
}
public String getCell(){
return cell;
}
public String getHome(){
return home;
}
public String getWork(){
return work;
}
// Modifier methods:
public void setName(String name){
this.name = name;
}
public void setSurname(String surname){
this.surname = surname;
}
public void setAddress (String address){
this.address = address;
}
public void setCell (String cell){
this.cell = cell;
}
public void setHome (String home){
this.home = home;
}
public void setWork (String work){
this.work = work;
}
public String toString(){
return name + " " + surname + " " + address + " " + cell + " " + home + " " + work;
}
public int compareTo(Person other){
if (!this.name.equalsIgnoreCase(other.name))
return this.name.compareTo(other.name);
return this.name + " "+other.name;
}
}
Your existing compareTo method has a problem, but removing it violates the implements Comparable contract, since you must provide a compareTo method.
public int compareTo(Person other) {
if (!this.name.equalsIgnoreCase(other.name))
return this.name.compareTo(other.name);
// next line returns a String, but the method needs to return an int
return this.name + " " + other.name;
}
You can instead rely more directly on the standard String compareTo:
public int compareTo(Person other) {
if ( this.name.equalsIgnoreCase( other.name ) ) { return 0 };
return this.name.compareTo( other.name );
}
If you didn't have the ignore case constraint you've coded for, this would simply be
public int compareTo(Person other) {
return this.name.compareTo( other.name );
}
As an aside, there is no reason to make address, cell, home, and work public — and that's generally bad practice.
In order to implement an interface you need to implement all the methods in that interface. You either remove implements Comparable part or add public int compareTo method to your class.
The rule of compareTo method is that :
- if this Person is greater than other , return 1
- if this Person is smaller than other , return -1
- if they are equal, return 0
Related
I have two classes: Position and Order. In Position class, fields like: name, price. In Order class field: quantity. My problem is how to display: name, price and quantity together in Order class. I thought about delete arraylist and make another one with position and quantity but I doubt it would help me.
package programming.com.pl;
public class Position {
private String name;
private double price = 0;
public Position(String name, double price){
this.name = name;
this.price = price;
}
public double getPrice() {
return price;
}
public String toString(){
String str = String.format("%4s,%4s", name,price);
return str;
}
}
public class Order {
private int quantity;
final private ArrayList<Position> positions = new ArrayList<Position>();
private int addedPosition;
public Order(int quantity) {
this.quantity = quantity;
}
private double calculateProduct() {
double sum = 0;
for (int i = 0; i < positions.size(); i++) {
sum = positions.get(i).getPrice();
}
return sum;
}
double sumOrder() {
double sum = 0;
for (Position x : positions) {
sum += calculateProduct();
}
return sum;
}
void addPosition(Position p) {
if (!positions.contains(p)) {
positions.add(p);
} else {
quantity++;
}
}
void deletePosition(int index) {
positions.remove(index);
}
public String toString() {
System.out.println("Order is: ");
for (Position p : positions) {
System.out.println(positions.toString());
}
return "Order sum is: " + sumOrder();
}
}
You already are overriding toString method in Position class so you just need to call that toString method on the position object when iterating the position objects from inside your Order class' toString() method.
And as #Federico points out in the comments you shouldn't System.out.println from toString methods. Just append to a string the details you require displaying and return that string.
You can achieve your desired result like so:
public class Position {
.
.
#Override
public String toString() {
return String.format("%4s,%4s\n", name, price);
}
}
public class Order {
.
.
#Override
public String toString() {
StringBuilder sb = new StringBuilder("Order details: \n");
sb.append("Quantity: ").append(quantity).append("\n");
for (Position p : positions) {
sb.append(p);
}
sb.append("Order sum is: ").append(sumOrder());
return sb.toString();
}
}
Alright I am stuck on how do I implement this binary search that will receive data from other classes.
I am trying to implement it in my own ADT.
I have implemented a List ADT manually but now I want to add in a search operation which utilizes binary search algorithm manually and doesn't uses any built in Java API.
Example this is my sorted list interface that I implemented manually.
public class SortedArrayList<T extends Comparable<T>> implements SortedListInterface<T>{
private boolean binarySearch(// What parameters should I receive from Student Object?) {
// This will be my binary search implementation
}
}
The problem is I will be creating a Student class where I will add the instances of the student class into the sortedArrayList above.
Like how am I going to receive the data to be put into the binary search algorithm in a generics typed sortedArrayList?
Do note I am not allowed to use any JAVA Built-IN API , everything must be implemented manually else I can finish this easily but its a pain now since its limited.
Example I want to binary search by Student name from Student's class. How will I need to implement and receive data into this manually implemented ADT of mine?
public class SortedArrayList<T extends Comparable<T>> implements SortedListInterface<T>{
private T[] list;
private boolean binarySearch(int first, int last, T desiredItem) {
int mid = (first + last) / 2;
if(desiredItem.getFullName().equals(list[mid])
// This part over here. How do I access attributes from Student class in this ADT so that I can access the data and do comparison for the binary search..
}
}
How do I access attributes from Student class into my own ADT so that I can do comparisons on binary search algorithm?!
I am literally stuck.
I would appreciate someone giving me directions.
I repeat again no BUILT-IN APIs from JAVA, implementation manually only
ADT SortedList Interface
public interface SortedListInterface <T extends Comparable<T>> {
public boolean add(T element);
public T get(int index);
public boolean search(T element);
public T remove(int index);
public void clear();
public int getLength();
public boolean isEmpty();
public boolean isFull();
}
ADT SortedList Implementation Code
public class SortedArrayList<T extends Comparable<T>> implements SortedListInterface<T>{
//Data Types
private T[] list;
private int length;
private static final int SIZE = 10;
// Constructors
public SortedArrayList() {
this(SIZE);
}
public SortedArrayList(int size) {
length = 0;
list = (T[]) new Comparable[SIZE]; // an array of instances of a class implementing Comparable interface and able to use compareto method but its overidden instead
}
// Setter & Getters
#Override
public int getLength() {
return length;
}
#Override
public boolean isEmpty() {
return length == 0;
}
#Override
public boolean isFull() {
return false;
}
#Override
public void clear() {
length = 0;
}
// Array Expansion
private boolean isArrayFull() {
return length == list.length;
}
private void expandArray() {
T[] oldList = list;
int oldSize = oldList.length;
list = (T[]) new Object[2 * oldSize];
for (int i = 0; i < oldSize; i++) // copy old array elements into new array elements
list[i] = oldList[i];
}
// ADT METHODs
// Add New Elements Function
#Override
public boolean add(T element) {
int i = 0;
while (i < length && element.compareTo(list[i]) > 0) // return 0 with equal , return more than 1 if element larger than list[i] , return -1 if less
i++;
makeRoom(i + 1);
list[i] = element;
length++;
return true;
}
private void makeRoom(int index) { // accepts given index
int newIndex = index - 1;
int lastIndex = length - 1;
for (int i = lastIndex; i >= newIndex; i--)
list[i + 1] = list[i];
}
//Remove Elements Function
#Override
public T remove(int index) { // accepts given index
T result = null;
if ( index >= 1 && index <= length ) {
result = list[index - 1];
if (index < length)
removeGap(index);
length--;
}
return result;
}
private void removeGap(int index) { // accepts given index and remove the gap where the element its removed
int removedIndex = index - 1;
int lastIndex = length - 1;
for (int i = removedIndex; i < lastIndex; i++)
list[i] = list[i + 1]; // shifts elements back to remove the gap
}
// Get Element
#Override
public T get(int index) { // accepts given index and return the object
T object = null;
if ( index >= 1 && index <= length)
object = list[index - 1];
return object;
}
// Search Algorithms
#Override
public boolean search(T element) {
return binarySearch(element);
}
private boolean binarySearch(// Implementation here) {
// Implementation here
}
//To String Method
#Override
public String toString() {
String result = "";
for (int i = 0; i < length; i++)
result += list[i] + "\n";
return result;
}
}
Student Class Implementation
public class Student implements Comparable<Student>{
// Data Types
private Name name;
private char gender;
private String icNo;
private String mobileNo;
private Course course;
private int group;
private String dOB;
// Constructors
public Student() {
}
public Student(Name name, char gender, String icNo, String mobileNo, Course course, int group, String dOB) {
this.name = name;
this.gender = gender;
this.icNo = icNo;
this.mobileNo = mobileNo;
this.course = course;
this.group = group;
this.dOB = dOB;
}
public Student(Name name) {
this.name = name;
}
// setter
public void setName(Name name) {
this.name = name;
}
public void setGender(char gender) {
this.gender = gender;
}
public void setIcNo(String icNo) {
this.icNo = icNo;
}
public void setMobileNo(String mobileNo) {
this.mobileNo = mobileNo;
}
public void setCourse(Course course) {
this.course = course;
}
public void setGroup(int group) {
this.group = group;
}
public void setdOB(String dOB) {
this.dOB = dOB;
}
// getter
public Name getName() {
return name;
}
public char getGender() {
return gender;
}
public String getIcNo() {
return icNo;
}
public String getMobileNo() {
return mobileNo;
}
public Course getCourse() {
return course;
}
public int getGroup() {
return group;
}
public String getdOB() {
return dOB;
}
#Override
public String toString() {
return "Student{" + "name=" + name + ", gender=" + gender + ", icNo=" + icNo + ", mobileNo=" + mobileNo + ", course=" + course + ", group=" + group + ", dOB=" + dOB + '}';
}
public int compareTo(Student object) { // Sort according to name if name same then sort according to gender and so on.
int c = this.name.getFullName().compareTo(object.getName().getFullName());
if(c == 0)
c = this.gender - object.getGender();
if(c == 0)
c = this.icNo.compareTo(object.getIcNo());
if(c == 0)
c = this.mobileNo.compareTo(object.getMobileNo());
if(c == 0)
c = this.group - object.getGroup();
if(c == 0)
c = this.dOB.compareTo(object.getdOB());
return c;
}
}
Course Class
public class Course {
// Data Types
private String courseCode;
private String courseName;
private double courseFee;
// Constructors
public Course() {
}
public Course(String courseCode, String courseName, double courseFee) {
this.courseCode = courseCode;
this.courseName = courseName;
this.courseFee = courseFee;
}
// setter
public void setCourseCode(String courseCode) {
this.courseCode = courseCode;
}
public void setCourseName(String courseName) {
this.courseName = courseName;
}
public void setCourseFee(double courseFee) {
this.courseFee = courseFee;
}
// getter
public String getCourseCode() {
return courseCode;
}
public String getCourseName() {
return courseName;
}
public double getCourseFee() {
return courseFee;
}
#Override
public String toString() {
return "CourseCode = " + courseCode + "Course Name = " + courseName + "Course Fee = " + courseFee;
}
}
Name Class
public class Name {
// Data Types
private String firstName;
private String lastName;
// Constructors
public Name() {
}
public Name(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
// setter
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
// getter
public String getFirstName() {
return firstName;
}
public String getLastName() {
return lastName;
}
public String getFullName(){
return firstName + " " + lastName;
}
#Override
public String toString() {
return "Name{" + "firstName=" + firstName + ", lastName=" + lastName + '}';
}
The binary search algorithm relies on comparing a value being searched for with values in the list being searched. That's why the declaration of your class that implements the SortedListInterface is:
SortedArrayList<T extends Comparable<T>>
Note the extends Comparable<T>.
Comparable is an interface through which you can compare two objects. Hence in the search() method that you have to implement, you know that every object in the list defines the compareTo() method and you simply use that method to compare the object being searched for with individual objects in the list.
Here is a simple implementation of the binary search algorithm in the context of your project.
private T[] list; // The list to search.
private int count; // The number of non-null elements in 'list'.
public boolean search(T element) {
boolean found = false;
int lo = 0;
int hi = count - 1;
while (lo <= hi) {
int mid = (lo + hi) / 2;
if (list[mid].compareTo(element) < 0) {
lo = mid + 1;
}
else if (list[mid].compareTo(element) > 0) {
hi = mid - 1;
}
else {
found = true;
break;
}
}
return found;
}
With a method, you have a method parameter. In the method code you use the parameter name. But when you invoke that method from other code, you provide a value which is substituted for the parameter. In the same way, the code above uses a type parameter which is substituted with the name of an actual class when you create an instance of class SortedArrayList. In your case, T is substituted with Student and class Student must implement the compareTo() method. Hence method search(), in class SortedArrayList does not need to know about the members in class Student.
So you would first create an instance of SortedArrayList like this:
SortedArrayList<Student> theList = new SortedArrayList<>();
Then you can call the search() method like this:
Student s = new Student(/* relevant parameter values */);
theList.search(s);
EDIT
I understand that you don't necessarily want to search for a Student, you may want to search for the Name of a student or a student's mobile phone number. In that case I believe you need a Comparator. Here is the code for class SortedArrayList with the addition of a Comparator
import java.util.Comparator;
import java.util.Objects;
public class SortedArrayList<T extends Comparable<T>> implements SortedListInterface<T> {
private static final int SIZE = 10;
private Comparator<? super T> comparator;
private T[] list;
private int count;
#SuppressWarnings("unchecked")
public SortedArrayList(Comparator<? super T> c) {
comparator = c;
list = (T[]) new Comparable[SIZE]; // No way to verify that 'list' only contains instances of 'T'.
/* NOTE: Following is not allowed.
list = new T[SIZE]; // Cannot create a generic array of T
*/
}
#Override
public boolean add(T element) {
Objects.requireNonNull(element, "Cannot add null element.");
boolean result = false;
if (count == 0) {
list[0] = element;
count = 1;
result = true;
}
else {
if (!isFull()) {
int i = 0;
while (list[i] != null) {
if (element.compareTo(list[i]) < 0) {
break;
}
i++;
}
if (list[i] != null) {
for (int j = count - 1; j >= i; j--) {
list[j + 1] = list[j];
}
}
list[i] = element;
count++;
result = true;
}
}
return result;
}
#Override
public T get(int index) {
checkIndex(index);
return list[index];
}
#Override
public boolean search(T element) {
if (comparator == null) {
return binarySearchComparable(element);
}
else {
return binarySearchComparator(element);
}
}
#Override
public T remove(int index) {
checkIndex(index);
T removed = list[index];
list[index] = null;
for (int i = index; i < count; i++) {
list[i] = list[i + 1];
}
count--;
list[count] = null;
return removed;
}
#Override
public void clear() {
for (int i = 0; i < count; i++) {
list[i] = null;
}
count = 0;
}
#Override
public int getLength() {
return count;
}
#Override
public boolean isEmpty() {
return count == 0;
}
#Override
public boolean isFull() {
return count == SIZE;
}
private boolean binarySearchComparable(T element) {
boolean found = false;
int lo = 0;
int hi = count - 1;
while (lo <= hi) {
int mid = (lo + hi) / 2;
if (list[mid].compareTo(element) < 0) {
lo = mid + 1;
}
else if (list[mid].compareTo(element) > 0) {
hi = mid - 1;
}
else {
found = true;
break;
}
}
return found;
}
private boolean binarySearchComparator(T key) {
int low = 0;
int high = count - 1;
while (low <= high) {
int mid = (low + high) >>> 1;
T midVal = list[mid];
int cmp = comparator.compare(midVal, key);
if (cmp < 0)
low = mid + 1;
else if (cmp > 0)
high = mid - 1;
else
return true; // key found
}
return false; // key not found.
}
private void checkIndex(int index) {
if (index < 0) {
throw new IllegalArgumentException("Negative index.");
}
if (index >= count) {
throw new IllegalArgumentException(String.format("Supplied index %d is not less than %d", index, count));
}
}
}
Here is an example Comparator for the Name of a Student
import java.util.Comparator;
public class NameComparator implements Comparator<Student> {
#Override
public int compare(Student student1, Student student2) {
int result;
if (student1 == null) {
if (student2 == null) {
result = 0;
}
else {
result = -1;
}
}
else {
if (student2 == null) {
result = 1;
}
else {
result = student1.getName().getFullName().compareTo(student2.getName().getFullName());
}
}
return result;
}
}
So in order to search the list according to any combination of Student attributes, simply implement an appropriate Comparator and pass it to the SortedArrayList class.
EDIT 2
Following your comments from November 17, 2019.
Below is code for a "name and mobile" Comparator. As I wrote in my previous Edit, you need to write an appropriate Comparator for a given combination of Student attributes.
import java.util.Comparator;
/**
* Compares {#code Student} name and mobile phone number.
*/
public class NameAndMobileComparator implements Comparator<Student> {
#Override
public int compare(Student student1, Student student2) {
int result;
if (student1 == null) {
if (student2 == null) {
result = 0;
}
else {
result = -1;
}
}
else {
if (student2 == null) {
result = 1;
}
else {
result = student1.getName().getFullName().compareTo(student2.getName().getFullName());
if (result == 0) {
result = student1.getMobileNo().compareTo(student2.getMobileNo());
}
}
}
return result;
}
}
I have created a simple Queue of type which is also contains a print() function to it.
public class ArrayQueue implements Queue {
private T[] theArray;
private int currentSize;
private int front;
private int back;
private static final int DEFAULT_CAPACITY = 10;
public ArrayQueue() {
theArray = (T[]) new Object[DEFAULT_CAPACITY];
currentSize = 0;
front = 0;
back = -1;
}
public boolean isEmpty() {
return currentSize == 0;
}
public T dequeue() throws EmptyQueueException {
if (isEmpty())
throw new EmptyQueueException("ArrayQueue dequeue error");
T returnValue = theArray[front];
front = increment(front);
currentSize--;
return returnValue;
}
public void enqueue(T x) {
if (currentSize == theArray.length)
doubleQueue();
back = increment(back);
theArray[back] = x;
currentSize++;
}
private int increment(int x) {
if (++x == theArray.length)
x = 0;
return x;
}
public void print() {
if (isEmpty()) {
System.out.printf("Empty queue\n");
return;
}
System.out.printf("The queue is: ");
for (int i = front; i != back; i = increment(i)) {
System.out.print(theArray[i] + " ");
}
System.out.print(theArray[back] + "\n");
}
I have also created a Song object with 3 variables
public class Song {
private int id;
private String name;
private int likes;
public Song() {
this(1,"Test",10);
}
public Song(int id,String name, int likes) {
}
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 int getLikes() {
return likes;
}
public void setLikes(int likes) {
this.likes = likes;
}
Is there a way modify this function in order to print a specific object's information or do i need to write a different print method during my implementation?
For example i would like my Print method to show all the objects variables , if i call just like this is will only get the object pointer
ArrayQueue<Song> arrayQueue = new ArrayQueue<Song>();
Queue<Song> queue = arrayQueue; //arrayQueue instance is also a Queue
Song s = new Song();
arrayQueue.enqueue(s);
arrayQueue.print();
Result is
The queue is: Song#15db9742
My modification would print :
The queue is : 1 Test 10
You need to override the toString() method of Song.
For example, add this to Song:
#Override
public String toString() {
return id + " " + name + " " + likes;
}
How can I achieve a custom sorting to the content of field name:
first element: P followed by numbers [1-9]{2} always on first
followed by : P followed by numbers 0[0-9]
followed by : S
followed by numbers [1-9]{2}
and then the rest in normal order i1.getName().compareToIgnoreCase(i2.getName())
private static Comparator<Item> itemComperator = new Comparator<Item>() {
#Override
public int compare(Item i1, Item i2) {
if (i1.getName().matches("P[1-9]{2}") && i2.getName().matches("P0[0-9]"))
return -1;
else if (i1.getName().matches("S[1-9]{2}"))
return -1;
else
return i1.getName().compareToIgnoreCase(i2.getName());
}
};
#Test
public void sortItem() {
Item item01 = new Item(1, "R59");
Item item02 = new Item(2, "S48");
Item item03 = new Item(3, "P01");
Item item04 = new Item(4, "P25");
Item item05 = new Item(5, "R99");
List<Item> items = Arrays.asList(item01, item02, item03, item04, item05);
System.out.println("before sorting");
long seed = System.nanoTime();
Collections.shuffle(items, new Random(seed));
for (Item i : items) {
System.out.println(i.getId() + " " + i.getName());
}
System.out.println("after sorting");
Collections.sort(items, itemComperator);
for (Item i : items) {
System.out.println(i.getId() + " " + i.getName());
}
}
public class Item {
private int id;
private String name;
public Item(int id, String name) {
this.id = id;
this.name = name;
}
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;
}
}
output expected:
after sorting
4 P25
3 P01
2 S48
1 R59
5 R99
I think that I would first map each of the inputs to a "kind" number, which is based upon the list of criteria above. For example:
int kind(String input) {
if (input.matches("P[1-9]{2}") {
return 0;
} else if (input.matches("P0[0-9]")) {
return 1;
} else if (input.matches("S.*")) {
return 2;
} else if (input.matches("[1-9]{2}")) {
return 3;
} else {
return 4;
}
}
This gives you a way to see if the two strings are of the same "kind"; if not, return the ordering based on the kind. If they are the same kind, just compare them using (case insensitive) lexicographic ordering (you don't specify, but I assume you want e.g. "P11" to come before "P22"):
public int compare(Item a, Item b) {
String nameA = a.getName();
String nameB = b.getName();
int kindA = kind(nameA);
int kindB = kind(nameB);
if (kindA != kindB) {
return Integer.compare(kindA, kindB);
} else {
return nameA.compareToIgnoreCase(nameB);
}
}
I'm trying to do this exercise: i have a student that has a name,surname and a number, i want to order the students by number..if i want to order by name or surname it seems easy but with number i don't know how to do..
this is my code:
public class Student implements Comparable<Student> {
private String name;
private String surname;
private int number;
public Student(String n, String s, int m) {
name = n;
surname = s;
number = m;
}
public String getName() {
return name;
}
public String getSurname() {
return surname;
}
public int getmatricola() {
return number;
}
//CompareTo Name
public int compareTo(Student otherObject) {
return name.compareTo(otherObject.getName());
}
}
//TESTER
ArrayList<Student> list = new ArrayList<Student>();
System.out.print("\n ORDER BY NUMBER \n");
Collections.sort(list);
for (int i = 0; i < list.size(); i++) {
Student s = list.get(i);
String std = s.getAll();
System.out.println(std);
}
You can implement something like:
public int compareTo(Student otherObject) {
return Integer.compare(this.number, otherObject.getNumber());
}
So why you number is an int you can substract the number and return the difference:
public class Student implements Comparable<Student> {
private String name;
private String surname;
private int number;
public Student(String n, String s, int m) {
name = n;
surname = s;
number = m;
}
public String getName() {
return name;
}
public String getSurname() {
return surname;
}
public int getmatricola() {
return number;
}
//CompareTo number
public int compareTo(Student otherObject) {
return number - otherObject.getmatricola();
}
}
Try doing this...should work
//CompareTo Name
public int compareTo(Student otherObject) {
if( this.getmatricola() > otherObject.getmatricola())
return 1;
else
return -1;
}