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Access other Java classes

I am a Java beginner and two questions boggle me really hard, so I have these questions.
For instance, I do not understand why in the Class Suitcase the method call getWeight() can be called, but in the Class Hold the method call totalWeight() not.
It works here:
public int totalWeight() {
int momentaryWeight = 0;
for (Item items: this.itemList) {
momentaryWeight = momentaryWeight + items.getWeight();
}
return momentaryWeight;
}
But not here:
public String toString() {
int momentaryWeight = 0;
int index = 0;
for (int i = index; i < this.suitcaseList.size(); i++) {
Suitcase suitcaseChosen = this.suitcaseList.get(i);
int weightOfsuitcaseChosen = suitcaseChosen.totalWeight();
momentaryWeight += weightOfsuitcaseChosen;
}
Also when having a method that returns something and using an if statement (so 2 return statements) it asks me afterwards for another return statement, like here:
public Item printGoods() {
if (this.itemList.isEmpty() == true) {
return null;
} else {
for (Item itemThis: this.itemList) {
return itemThis;
}
}
return null;
}
I know that maybe these are dull questions, but I couldn't think of a better forum to understand it.
Thanks.
The Hold class:
public class Hold {
private int maxWeight;
private ArrayList<Suitcase> suitcaseList;
public Hold(int maxWeightGiven) {
this.maxWeight = maxWeightGiven;
this.suitcaseList = new ArrayList<>();
}
public void addSuitcase(Suitcase suitcase) {
this.suitcaseList.add(suitcase);
}
public String toString() {
int momentaryWeight = 0;
int index = 0;
for (int i = index; i < this.suitcaseList.size(); i++) {
Suitcase suitcaseChosen = this.suitcaseList.get(i);
int weightOfsuitcaseChosen = suitcaseChosen.totalWeight();
momentaryWeight += weightOfsuitcaseChosen;
}
return this.suitcaseList.size() + " suitcases" + " (" + momentaryWeight + " kg)";
}
The Suitcase class:
import java.util.ArrayList;
public class Suitcase {
private int maximumWeight;
private ArrayList<Item> itemList;
public Suitcase(int maximumWeightGiven) {
this.maximumWeight = maximumWeightGiven;
this.itemList = new ArrayList<>();
}
public void addItem(Item item) {
int momentaryWeight = 0;
if (momentaryWeight <= this.maximumWeight && momentaryWeight + item.getWeight() <= this.maximumWeight) {
this.itemList.add(item);
}
}
public int totalWeight() {
int momentaryWeight = 0;
for (Item items: this.itemList) {
momentaryWeight = momentaryWeight + items.getWeight();
}
return momentaryWeight;
}
The class Item looks like this:
public class Item {
private String name;
private int weight;
public Item(String nameGiven, int weightGiven) {
this.name = nameGiven;
this.weight = weightGiven;
}
public String getName() {
return this.name;
}
public int getWeight() {
return this.weight;
}
public String toString() {
return this.name + "( " + this.weight + " kg)";
}
}
}

First question is incomplete code and detail.
Second question: suppose if-condition is false and your loop condition is also false(empty array) then the program will not reach to return statement that's why you have to add an extra return statement.
You can move last return line inside the else block

Don't know what happened, but as I worked on it a while later, suddenly the error messages disappeared and I was able to run the program. Is there a special key in NetBeans for "Refreshing"?

How to Implement Binary Search Manually In My Own ADT [ JAVA ]

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;
}
}

Compare Duplicate Data From a List with Inputed Data

I want to check duplicate IDs from a list with the data I inputted, then increment the qty variable in the list. If it's new data, it will add a new list.
This is my code
public void addBarang(Barang barang){
int id_barang = barang.getId();
if(this.list.isEmpty())
{
list.add(barang);
}
else
{
for(int i=0;i<list.size();i++)
{
if(list.get(i).getId() != id_barang)
{
list.add(barang);
System.out.println("Added");
break;
}
if(list.get(i).getId() == id_barang)
{
int new_qty = list.get(i).getQty()+barang.getQty();
list.get(i).setQty(new_qty);
}
}
}
}
Even if I input new data it always increments the qty of old data and the new data is not added (basically always end in the "else" section).
Code for inputing data
Gudang gudang1 = new Gudang(1,1);
System.out.println("ID: ");
int id = input.nextInt();
System.out.println("Jumlah: ");
int qty = input.nextInt();
System.out.println("Nama: ");
String name = input.next();
Barang barang = new Barang(id,name,qty);
gudang1.addBarang(barang);
Barang Class
public class Barang {
public static int id;
private String name;
private int qty;
public Barang(int id, String name, int qty) {
this.id = id;
this.name = name;
this.qty = qty;
}
public Barang(){
};
public int getId() {
return id;
}
public String getName() {
return name;
}
public int getQty() {
return qty;
}
public void setId(int id) {
this.id = id;
}
public void setName(String name) {
this.name = name;
}
public void setQty(int qty) {
this.qty = qty;
}
#Override
public String toString() {
return "Barang{" + "id=" + id + ", name=" + name + ", qty=" + qty + '}';
}
Gudang Class
public class Gudang {
public static int id;
private int location;
public List<Barang> list = new ArrayList<Barang>();
public Gudang(int id, int location) {
Gudang.id = id;
this.location = location;
}
public int getId() {
return id;
}
public int getLocation() {
return location;
}
public List<Barang> getList() {
return list;
}
public void setId(int id) {
this.id = id;
}
public void setLocation(int location) {
this.location = location;
}
public void setList(List<Barang> list) {
this.list = list;
}
public void addBarang(Barang barang){
int id_barang = barang.getId();
if(this.list.isEmpty())
{
list.add(barang);
}
else
{
for(int i=0;i<list.size();i++)
{
if(list.get(i).getId() != id_barang)
{
list.add(barang);
System.out.println("Added");
break;
}
if(list.get(i).getId() == id_barang)
{
int new_qty = list.get(i).getQty()+barang.getQty();
list.get(i).setQty(new_qty);
}
}
}
System.out.println("Size List = "+list.size());
}
public void duplicate(List<Barang> list2)
{
this.list.addAll(list2);
}
public void clearBarang(){
this.list.clear();
}
public void display(){
for(Barang barang: this.list){
System.out.println(barang);
}
}
IE : If I have id=1 and qty=1, then input a new data with id=2 and qty=2, the final result will end up with id=2 and qty=3. No new data int he list were added.

try using .equals to compare if the data exist in your list

Please check if ids are duplicate between your old and new data.
If you ids are unique then you can take advantage of Map and put id as key and barang object as value. Whenever you successfully lookup map increment quantity field of object.

At first guess i would change:
if(list.get(i).getId() != id_barang)
to:
if(list.get(i).getId() != barang.getId())
maybe id_barang is not the same as the id stored in the barang object.

Sorting a linkedList by the value of the object

For an assignment, I've been tasked to create a priority based support ticket system which contains the user's Name, ID, Handler and Priority however ticket's with higher priority are placed first in the list to be dealt with.
I have three classes.
Main: where I add/delete and change ticket priority.
TicketSystem: Contains the constructor for the ticket alongside getters and setter methods
LinkedList: Has insert, delete printList and should have sortList
So far I've determined the algorithm needs to be bubblesort as Priority is an int value but I'm not too sure how to receive the value for priority and then sort it.
public class TicketSystem {
private String handler;
private int priority;
private String iD;
private String creator;
public TicketSystem() {
}
public String getHandler ( ) {
return handler;
}
public int getPriority () {
return priority;
}
public String getID () {
return iD;
}
public String creator () {
return creator;
}
public void setID (String i) {
this.iD = i;
}
public void setHandler (String h) {
this.handler = h;
}
public void setPriority (int p ) {
this.priority = p;
}
public String setCreator (String c) {
return this.creator = c;
}
public void addTicket( String h, int p, String c, String iD) {
this.handler = h;
this.priority = p;
this.iD = iD;
this.creator = c;
}
#Override
public String toString() {
String output = "";
output += "Handler: " + handler +", ";
output += "Priority: " + priority + ", ";
output += "Creator: " + creator + ", ";
output += "ID: " + iD + " ";
return output;
}
}
public class LinkedList {
private Node head;
public LinkedList(TicketSystem ticket) {
head = new Node();
head.ticket = ticket;
head.link = null;
}
public boolean insertItem(TicketSystem ticket) {
Node n = new Node();
Node new_node;
new_node = head;
while (new_node.link != null) {
new_node = new_node.link;
}
n.ticket = ticket;
n.link = null;
new_node.link = n;
return true;
}
public void printList() {
Node z = head;
while (z!= null) {
System.out.println(z.ticket.toString());
z = z.link;
}
}
public boolean deleteItem(TicketSystem ticket) {
if(ticket.equals(head.ticket)) {
head = head.link;
return true;
} else {
Node prevNode = head;
Node curNode = head.link;
while(curNode != null && !(curNode.ticket == ticket)) {
prevNode = curNode;
curNode = curNode.link;
}
if(curNode != null) {
prevNode.link = curNode.link;
return true;
} else {
return false;
}
}
}
/* sort list */
public void sortList() {
TicketSystem ts = new TicketSystem();
}
class Node {
private TicketSystem ticket;
private Node link;
}
}

Add objects with random variables using a loop

I am trying to write a program where I ask to the user how many persons he wants to implement in this world. Afterwards, I would like as many person objects as the user answered. I defined a person class with a person constructor containing all person variables ( + getters/setters). After this, I tried to create a loop to assign values to my variables (most of them happen random). Currently, I set the number of instances I want to create to 20 (arbitrary).
This is my person class
public class Person implements Item {
public static final int MAX_AGE = 70;
public static final int MAX_SEX_APPEAL = 10;
public static final int MAX_AGRESSION_LEVEL = 10;
public static final int MAX_STRENGTH = 10;
private int id;
private int age;
private boolean gender;
private int sexAppeal;
private int agressionLevel;
private int strength;
private boolean isAlive;
public Person (int id, int age, boolean gender, int sexAppeal, int agressionLevel, int strength, boolean isAlive){
this.setId(id);
this.setAge(age);
this.setGender(gender);
this.setSexAppeal(sexAppeal);
this.setAgressionLevel(agressionLevel);
this.setStrength(strength);
this.setAlive(isAlive);
}
void getBorn () {
isAlive = true;
age = 0;
// a new people is born
// age = 0
// other variables: random
}
void die () {
isAlive = false;
// people die when they reach the max age
// people die when being on the same cell as vulcanos
// people can be murdered
// setAlive = false
}
void murder () {
// when 2 people with min agression level on the same land ==> weakest one dies
}
void move () {
// method to make people move
// random (only to adjucant fields)
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public boolean isGender() {
return gender;
}
public void setGender(boolean gender) {
this.gender = gender;
}
public int getSexAppeal() {
return sexAppeal;
}
public void setSexAppeal(int sexAppeal) {
this.sexAppeal = sexAppeal;
}
public int getAgressionLevel() {
return agressionLevel;
}
public void setAgressionLevel(int agressionLevel) {
this.agressionLevel = agressionLevel;
}
public int getStrength() {
return strength;
}
public void setStrength(int strength) {
this.strength = strength;
}
public boolean isAlive() {
return isAlive;
}
public void setAlive(boolean isAlive) {
this.isAlive = isAlive;
}
}
And this is my "test class" where I try to create 20 instances :
import java.util.concurrent.ThreadLocalRandom;
public class test {
public static void main(String[] args) {
for (int i = 0; i < 20; i ++) {
Person person(i) = new Person();
person.setId(i);
person.setAge(ThreadLocalRandom.current().nextInt(0, Person.MAX_AGE + 1));
person.setGender((Math.random() < 0.5));
person.setSexAppeal(ThreadLocalRandom.current().nextInt(0, Person.MAX_SEX_APPEAL + 1));
person.setAgressionLevel(ThreadLocalRandom.current().nextInt(0, Person.MAX_SEX_APPEAL + 1));
person.setStrength(ThreadLocalRandom.current().nextInt(0, Person.MAX_SEX_APPEAL + 1));
person.setAlive(true);
}
}
}
However, I am getting the following error at this line
Person person(i) = new Person();
The constructor Person () is undefined
Type mismatch: cannot convert from Person to int
I understand those errors but I don't know another way to become to the result I want to achieve

You should make a list and just add the created persons to it.
public class test {
public static void main(String[] args) {
List<Person> persons = new ArrayList<>(); // create a list to store the generated persons
for (int i = 0; i < 20; i++) {
Person person = new Person(); // generate a person
person.setId(i);
person.setAge(ThreadLocalRandom.current().nextInt(0, Person.MAX_AGE + 1));
person.setGender((Math.random() < 0.5));
person.setSexAppeal(ThreadLocalRandom.current().nextInt(0, Person.MAX_SEX_APPEAL + 1));
person.setAgressionLevel(ThreadLocalRandom.current().nextInt(0, Person.MAX_SEX_APPEAL + 1));
person.setStrength(ThreadLocalRandom.current().nextInt(0, Person.MAX_SEX_APPEAL + 1));
person.setAlive(true);
persons.add(person); /// add the generated person to the list
}
}
}
Also if you want to call the Person constructor without parameters the class must have a constructor that takes no parameters.
public Person() {}