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How to implement a Java Hashmap with different objects as values

I want to parse a YAML-file via Jackson but encounter the problem that one of the properties (let's call it 'Event') has a string called 'type' and a 'properties' object that differs for different Events. My issue is that I need to define the POJOs for this YAML. Therefore, I want to define a Hashmap with VariableObject that can be any of some predefined classes (for brevity, let's say Shipping and Inventory).
How can I implement a Hashmap like that?
public class Event {
private static String type;
private static Map<String, VariableObject> properties;
public static void main(String[] args) {
Inventory inventory = new Inventory("inventoryName", 13);
properties.put("Inventory", inventory);
Shipping shipping = new Shipping("shippingName", true);
properties.put("Shipping", shipping);
}
}
public class Inventory {
private static String name;
private static int someNumber;
public Inventory(String name, int someNumber) {
this.name = name;
this.someNumber = someNumber;
}
}
public class Shipping {
private static String name;
private static boolean someBoolean;
public Shipping(String name, boolean someBoolean) {
this.name = name;
this.someBoolean = someBoolean;
}
}

What you're talking ablut is simple Object. It's the most specific common superclass:
private static Map<String, Object> properties;
Other solution would be to make Inventory and Shipping implement some common interface, for example Named and use it as type parameter in HashMap.

One way to do this is to make Shipping and Inventory implements the same interface (like VariableObject in your cas)
public class Event {
private static String type;
private static Map<String, VariableObject> properties;
public static void main(String[] args) {
Inventory inventory = new Inventory("inventoryName", 13);
properties.put("Inventory", inventory);
Shipping shipping = new Shipping("shippingName", true);
properties.put("Shipping", shipping);
}
}
public interface VariableObject{
//you can define common methods here if you want
}
public class Inventory implements VariableObject{
private static String name;
private static int someNumber;
public Inventory(String name, int someNumber) {
this.name = name;
this.someNumber = someNumber;
}
}
public class Shipping implements VariableObject{
private static String name;
private static boolean someBoolean;
public Shipping(String name, boolean someBoolean) {
this.name = name;
this.someBoolean = someBoolean;
}
}

Get all objects with the same constructor as integer?

I got the following class:
public class Possibility {
private String name;
public Possibility(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
If I now have many classes that extend "Possibility", how can I find how many instances exist of classes that extend Possibility?

You can use a static field as a counter in Possibility class and use it to increment as the objects are created. This is more efficient and secure than using reflection.
package so;
public class Possibility {
private static int counter = 0;
private String name;
public Possibility(String name) {
counter += 1;
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public static void main(String[] args) {
Possibility1 p1 = new Possibility1("p1");
Possibility2 p2 = new Possibility2("p2");
System.out.println(Possibility.counter);
}
}
Possibility1
package so;
public class Possibility1 extends Possibility {
public Possibility1(String name) {
super(name);
}
}
Possibility2:
package so;
public class Possibility2 extends Possibility {
public Possibility2(String name) {
super(name);
}
}
Possibility3
package so;
public class Possibility3 extends Possibility {
public Possibility3(String name) {
super(name);
}
}

The Reflections library provides a pretty easy way to do this:
int numSubTypes = reflections.getSubTypesOf(Possibility.class).size();

you must create an integer attribute in Possibility class and and you can get this integer from another class that extends from Possibility, like this:
class Possibility{
public int someInteger;
//getter
public int getSomeInteger(){
return this.someInteger;
}
}
class someClass extends Possibility{
public void someMethode(){
Possibility possibility = new Possibility("someName");
//get someInteger
possibility.getSomeInteger();
}
}

Can a static final field be initialized in subclasses? If so, how?

I need to write some code which is as follows:
public class Person {
public static final String NAME;
public Person(String NAME) {
this.NAME = NAME;
}
}
public class Player extends Person {
public Peter(String name) {
super(name);
}
}
It's basically, I want the Player class to have a static final field called NAME, that is being initialized somewhere else, without manually writing in every class public static final String NAME = "Peter".
Is it possible?

As it has been said in the comments, you have poorly declared your NAME variable. In actuality, you don't want it to be static (although you can keep the final modifier, if you want). Your code should, instead, be something along the lines of:
public class Person {
public final String name;
public Person(String name) {
this.name = name;
}
}
public class Player extends Person {
public Player(String name) {
super(name);
}
}
Every person should have their own name; you don't want all objects to be sharing one NAME field

I do not know if I fully understand your question, but I think you have a few mistakes in your code. Like declare name of person as static variable, because static variables are often used as variables for the entire class, and if you changed the name, would change the name to the entire class, not for one instance. Also final is wrong, because you cannot set final variable.
I would do something like this:
public class Person {
private String name;
public Person(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
#Override
public String toString() {
return String.format("Person: %s", this.getName());
}
}
public class Player extends Person{
public Player(String name) {
super(name);
}
public String toString(){
return String.format("Player: %s", this.getName());
}
}
public class Match {
private Player player_one;
private Player player_two;
public Match(Player player_one, Player player_two) {
this.player_one = player_one;
this.player_two = player_two;
}
public Player getPlayer_one() {
return player_one;
}
public void setPlayer_one(Player player_one) {
this.player_one = player_one;
}
public Player getPlayer_two() {
return player_two;
}
public void setPlayer_two(Player player_two) {
this.player_two = player_two;
}
#Override
public String toString() {
return String.format("Right now are playing %s VS %s",player_one.getName(), player_two.getName());
}
}
public class PlayerTest {
public static void main(String[] args) {
Player peter = new Player("Peter");
Player anna = new Player("Anna");
Match tennisMatch = new Match(peter, anna);
System.out.println(tennisMatch.toString());
}
}

I static field (variable) only exists once for all instances of your class. Therefore what you try does not work by design.
What value would you expect the field to have after you created three different instances of this class using different parameters?
A final variable cannot be changed once it got initialized. For static variables this happens before the first instance of the class is even constructed. At the moment the constructor is executed the field cannot be changed anymore.
To initialize a static final variable you have to assign a value directly at the definition using the = operator or you have to do it in a static initializer which looks like this:
public class FooBar {
public static final String STATIC_VARIABLE;
static {
STATIC_VARIABLE = "Hello World";
}
}

You can make it like this:
private static final NAME;
public Player(String name){
NAME = name;
}
A final varible can be initialized once only if it wasn't initialized yet.
So in this way the constructor is helping you make it.

Printing the name of an object in Java

I have researched, and although this is a really simple issue, I am not sure how to solve it.
The code I have looks like this:
public class Playlist {
public Playlist(String name) {
}
}
Separate files of course:
#Test
public void CreatePlaylist(){
Playlist myPlaylist = new Playlist("Workout Playlist");
}
I am trying to print the actual name of this new playlist "workout playlist" but I can't seem to find a way to do so.

You need to store the name of your playlist in an instance variable. For instance:
public class Playlist {
private final String name;
public Playlist(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
Then you can print it with:
System.out.println(myPlayList.getName());
If you want to make the name mutable, then get rid of the final modifier and add a setName(String) method.

write get method to name or override toString method in the class
public class Playlist {
private String name;
public Playlist (String name) {
this.name = name;
}
public String getName() {
return name;
}
#Override
public String toString() {
return "Playlist [name=" + name + "]";
}
}
Print the name using
System.out.println(playlistObject.getName());
or
System.out.println(playlistObject).
I would prefer setting a getter method over toString() though.

public class Playlist {
private String name;
public Playlist(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
Then to show the name:
#Test
public void CreatePlaylist(){
Playlist myPlaylist = new Playlist("Workout Playlist");
System.out.println(myPlaylist.getName());
}

You are not at all storing the 'name' property in your object. So obviously you can't access name. One way is
public class Playlist {
public String name;
public Playlist(String name) {
this.name = name;
}
}
Now you should be able to access your attribute from your testcase like this.
#Test
public void CreatePlaylist(){
Playlist myPlaylist = new Playlist("Workout Playlist");
System.out.println(myPlaylist.name);
}

create a class to model a list

I have a class named Person.This class represents (as the name says) a Person. Now I have to create a class PhoneBook to represent a list of Persons. How can I do this? I don't understand what means "create a class to represent a list".
import java.util.*;
public class Person {
private String surname;
private String name;
private String title;
private String mail_addr;
private String company;
private String position;
private int homephone;
private int officephone;
private int cellphone;
private Collection<OtherPhoneBook> otherphonebooklist;
public Person(String surname,String name,String title,String mail_addr,String company,String position){
this.surname=surname;
this.name=name;
this.title=title;
this.mail_addr=mail_addr;
this.company=company;
this.position=position;
otherphonebooklist=new ArrayList<OtherPhoneBook>();
}
public String getSurname(){
return surname;
}
public String getName(){
return name;
}
public String getTitle(){
return title;
}
public String getMailAddr(){
return company;
}
public String getCompany(){
return position;
}
public void setHomePhone(int hp){
homephone=hp;
}
public void setOfficePhone(int op){
officephone=op;
}
public void setCellPhone(int cp){
cellphone=cp;
}
public int getHomePhone(){
return homephone;
}
public int getOfficePhone(){
return officephone;
}
public int getCellPhone(){
return cellphone;
}
public Collection<OtherPhoneBook> getOtherPhoneBook(){
return otherphonebooklist;
}
public String toString(){
String temp="";
temp+="\nSurname: "+surname;
temp+="\nName: "+name;
temp+="\nTitle: "+title;
temp+="\nMail Address: "+mail_addr;
temp+="\nCompany: "+company;
temp+="\nPosition: "+position;
return temp;
}
}

Your PhoneBook class will likely have a member like this:
private List<Person> book = new ArrayList<Person>();
And methods for adding and retrieving Person objects to/from this list:
public void add(final Person person) {
this.book.add(person);
}
public Person get(final Person person) {
int ind = this.book.indexOf(person);
return (ind != -1) ? this.book.get(ind) : null;
}
Note that a List isn't the best possible representation for a phone book, because (in the worst case) you'll need to traverse the entire list to look up a number.
There are many improvements/enhancements you could make. This should get you started.

Based on the class being named PhoneBook, I assume that you ultimately want to create a mapping between a phone number, and a person. If this is what you need to do then your PhoneBook class should contain a Map instead of a List (but this may depend on other parameters of the project).
public class PhoneBook
{
private Map<String,Person> people = new HashMap<String,Person>();
public void addPerson(String phoneNumber, Person person)
{
people.put(phoneNumber,person);
}
public void getPerson(String phoneNumber)
{
return people.get(phoneNumber);
}
}
In the above, the phone number is represented as a String, which is probably not ideal since the same phone number could have different String representations (different spacing, or dashes, etc). Ideally the Map key would be a PhoneNumber class that takes this all into account in its hashCode and equals functions.

you can do it by creating a class PhoneBook
public class PhoneBook{
Private List<Person> personList = new ArrayList<Person>;
public void addPerson(Person person){
this.personList.add(person);
}
public List getPersonList(){
return this.personList;
}
public Person getPersonByIndex(int index){
return this.personList.get(index);
}
}