Develop Reference

Cannot resolve method "compareTo(Friend)"

I'm creating a FriendList which extends ArrayList and is populated with a Friend object. However when I try accessing methods normally available to Friend, the compiler says it cannot resolve the method - in this case compareTo(Friend).
FriendList class:
public class FriendList<Friend> extends ArrayList<Friend> {
private boolean isAdded;
public FriendList() {
isAdded = false;
}
public void alphabetAdd(Friend friend) {
if (this.isEmpty()) {
add(friend);
return;
}
int index = 0;
// add friends alphabetically
while (!isAdded) {
Friend f = this.get(index+1);
if (f.compareTo(friend) < 0) {
index++;
} else {
this.add(index, friend);
isAdded = true;
}
}
}
}
Friend class:
public class Friend implements Comparable<Friend> {
// constructors and other methods work fine - just need to see compareTo
// #Override
public int compareTo(#NonNull Friend o) {
String name1 = getUserFirstName() + getUserLastName();
Friend f;
if (o instanceof Friend) {
f = (Friend) o;
String name2 = f.getUserFirstName() + f.getUserLastName();
if (name1.compareTo(name2) < 0)
return -1;
else if (name1.compareTo(name2) > 0)
return 1;
}
return 0;
}
}

The issue is in FriendList<Friend>. This is treated as a declaration of generic class like FriendList<T> and Friend becomes not an actual type but an alias that is why only methods declared in Object are available.
Change declaration of your class to
public class FriendList extends ArrayList<Friend>

How can I make this Serialization works?

The idea is about serialize this box code. The program is to build flashcard and I want use serializetion to saving the state of the flashapp boxes, when the application exits into a file, and load the file on startup. So I don't have to redo all the flashcard from the beginning. The box code is as follow:
import java.util.ArrayList;
import java.util.Iterator;
public class Box implements java.io.Serializable {
private ArrayList<Flashcard> cards;
private double prossibility;
private double pivot; //determine the box's selected scope [pivot - prossibility,pivot)
public Box(){
cards = new ArrayList<Flashcard>();
prossibility = 0.0;
pivot = 0.0;
}
public Box(double prossibility,double pivot){
this.cards = new ArrayList<Flashcard>();
this.prossibility = prossibility;
this.pivot = pivot;
}
public Box(ArrayList<Flashcard> cards){
this.cards = cards;
}
public ArrayList<Flashcard> getCards() {
return cards;
}
public void setProssibility(double prossibility){
this.prossibility = prossibility;
}
public double getProssibility(){
return prossibility;
}
public void setPivot(double pivot){
this.pivot = pivot;
}
public double getPivot(){
return pivot;
}
public void addCard(Flashcard card){
cards.add(card);
}
public int searchCard(String challenge){
Iterator<Flashcard> it = cards.iterator();
int index = 0;
while(it.hasNext()){
Flashcard temp = (Flashcard)it.next();
if(temp.getChallenge().equals(challenge)){
break;
}
++index;
}
if(index >= cards.size())
index = -1;
return index;
}
public void removeCard(String challenge){
int index = searchCard(challenge);
if(index >= 0)
cards.remove(index);
}
}
My flashcard class is like:
enum ESide{
FRONT, //challenge side
BACK //response side
};
public class Flashcard implements Cloneable{
private String challenge;
private String response;
private ESide side;
private int boxIndex;
public Flashcard(){
challenge = new String();
response = new String();
side = ESide.BACK;
boxIndex = 0;
}
public Flashcard(String challenge, String response, ESide side){
this.challenge = challenge;
this.response = response;
this.side = side;
this.boxIndex = 0;
}
public Flashcard(String challenge, String response){
this.challenge = challenge;
this.response = response;
this.side = ESide.BACK;
this.boxIndex = 0;
}
public void setChallenge(String challenge){
this.challenge = challenge;
}
public String getChallenge(){
return challenge;
}
public void setResponse(String response){
this.response = response;
}
public String getResponse(){
return response;
}
public void setSide(ESide side){
this.side = side;
}
public ESide getSide(){
return side;
}
public void setBoxIndex(int index){
this.boxIndex = index;
}
public int getBoxIndex(){
return boxIndex;
}
public void flipSide(){
if(side == ESide.BACK)
side = ESide.FRONT;
else
side = ESide.BACK;
}
public Object clone(){
Flashcard o = null;
try {
o = (Flashcard)super.clone();
} catch (CloneNotSupportedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return o;
}
public boolean equals(Object o){
if(this == o)
return true;
if(o == null)
return false;
if(!(o instanceof Flashcard))
return false;
Flashcard temp = (Flashcard)o;
if(!temp.challenge.equals(this.challenge) || !temp.response.equals(this.response)){
return false;
}
return true;
}
}
The serialize code I have done is like this:
import java.io.*;
public class Savingbox implements Serializable {
public static void main(String[] args){
Box e = new Box();
So how can I make the savingbox class save the result that the user just used?

From what I understand you want to save the Flashcard objects to a file and then read those back in. Here is a link that explains how to: How to write and read java serialized objects into a file

Java: HashSet multiple types

I have a program that I have to use a HashSet for. My question arises from the fact that HashSets mainly contain one object, but if I wish to send information to the other class, it takes three objects: one string, one int, and one boolean.
The assignment says that I must use a HashSet
Constructor I am trying to send information to:
public Magic (String name, int size, boolean isVisible)
I have a class that is supposed to be sending sets of spells containing name, size, and isVisible.
Magic.go() class:
public void go()
{
int i = 0;
while (i < size) {
if (isVisible == true) {
System.out.println(name + "!");
}
i++;
}
}

Just create an object which contains all the three fields like this:
import java.util.Objects;
public class NameSizeVisible {
private final String name;
private final int size;
private final boolean isVisible;
public NameSizeVisible(String name, int size, boolean isVisible) {
this.name = name;
this.size = size;
this.isVisible = isVisible;
}
public String getName() {
return name;
}
public int getSize() {
return size;
}
public boolean isVisible() {
return isVisible;
}
#Override
public int hashCode() {
return Objects.hash(name,size,isVisible);
}
#Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
NameSizeVisible other = (NameSizeVisible) obj;
if (isVisible != other.isVisible)
return false;
if (!Objects.equals(name, other.name))
return false;
if (size != other.size)
return false;
return true;
}
}

You can use a HashSet that stores Objects. So you would have:
HashSet<Object> set = new HashSet<>();
set.add(name);
set.add(size);
set.add(isVisible);
Then when you access the objects you just need to cast them to their respective types:
String name = "";
int size = 0;
boolean isVisible = false;
for (Object o : set) {
if (o instanceof String) {
name = (String) o;
} else if (o instanceof int) {
size = (int) o;
} else {
isVisible = (boolean) o;
}
}

Confusion on using instanceof along with other inherited data

I have already made a posting about this program once, but I am once again stuck on a new concept that I am learning (Also as a side note; I am a CS student so please DO NOT simply hand me a solution, for my University has strict code copying rules, thank you.). There are a couple of difficulties I am having with this concept, the main one being that I am having a hard time implementing it to my purposes, despite the textbook examples making perfect sense. So just a quick explanation of what I'm doing:
I have an entity class that takes a Scanner from a driver. My other class then hands off the scanner to a superclass and its two subclasses then inherit that scanner. Each class has different data from the .txt the Scanner read through. Then those three classes send off their data to the entity to do final calculations. And that is where my problem lies, after all the data has been read. I have a method that displays a new output along with a few methods that add data from the super along with its derived classes.EDIT: I simply cannot figure out how to call the instance variable of my subclasses through the super so I can add and calculate the data.
Here are my four classes in the order; Driver, Entity, Super, Subs:
public static final String INPUT_FILE = "baseballTeam.txt";
public static void main(String[] args) {
BaseballTeam team = new BaseballTeam();
Scanner inFile = null;
try {
inFile = new Scanner(new File(INPUT_FILE));
team.loadTeam(inFile);
team.outputTeam();
} catch (FileNotFoundException e) {
System.out.println("File " + INPUT_FILE + " Not Found.");
System.exit(1);
}
}
}
public class BaseballTeam {
private String name;
private Player[] roster = new Player[25];
Player pitcher = new Pitcher();
Player batter = new Batter();
BaseballTeam() {
name = "";
}
public String getName() {
return name;
}
public void setName(String aName) {
name = aName;
}
public void loadTeam(Scanner input) {
name = input.nextLine();
for (int i = 0; i < roster.length; i++) {
if (i <= 9) {
roster[i] = new Pitcher();
}
else if ((i > 9) && (i <= 19)) {
roster[i] = new Batter();
}
else if (i > 19) {
roster[i] = new Player();
}
roster[i].loadData(input);
roster[i].generateDisplayString();
//System.out.println(roster[i].generateDisplayString()); //used sout to test for correct data
}
}
public void outputTeam() {
if ((pitcher instanceof Player) && (batter instanceof Player)) {
for (int i = 0; i < roster.length; i++) {
System.out.println(roster[i].generateDisplayString());
}
}
//How do I go about doing calculates?
public int calculateTeamWins() {
if ((pitcher instanceof ) && (batter instanceof Batter)) {
}
return 0;
}
public int calculateTeamSaves() {
if ((pitcher instanceof Pitcher) && (batter instanceof Batter)) {
}
return 0;
}
public double calculateTeamERA() {
if ((pitcher instanceof Pitcher) && (batter instanceof Batter)) {
}
return 0;
}
public double calculateTeamWHIP() {
if ((pitcher instanceof Pitcher) && (batter instanceof Batter)) {
}
return 0;
}
public double calculateTeamBattingAverage() {
if ((pitcher instanceof Pitcher) && (batter instanceof Batter)) {
}
return 0;
}
public int calculateTeamHomeRuns() {
if ((pitcher instanceof Pitcher) && (batter instanceof Batter)) {
}
return 0;
}
public int calculateTeamRBI() {
if ((pitcher instanceof Pitcher) && (batter instanceof Batter)) {
}
return 0;
}
public int calculateStolenBases() {
if ((pitcher instanceof Pitcher) && (batter instanceof Batter)) {
}
return 0;
}
}
public class Player {
protected String name;
protected String position;
Player(){
name = "";
position = "";
}
public String getName() {
return name;
}
public void setName(String aName) {
name = aName;
}
public String getPosition() {
return position;
}
public void setPosition(String aPosition) {
position = aPosition;
}
public void loadData(Scanner input){
do {
name = input.nextLine();
} while (name.equals(""));
position = input.next();
//System.out.println(generateDisplayString());
}
public String generateDisplayString(){
return "Name: " + name + ", Position:" + position;
}
}
public class Pitcher extends Player {
private int wins;
private int saves;
private int inningsPitched;
private int earnedRuns;
private int hits;
private int walks;
private double ERA;
private double WHIP;
Pitcher() {
super();
wins = 0;
saves = 0;
inningsPitched = 0;
earnedRuns = 0;
hits = 0;
walks = 0;
}
public int getWins() {
return wins;
}
public void setWins(int aWins) {
wins = aWins;
}
public int getSaves() {
return saves;
}
public void setSaves(int aSaves) {
saves = aSaves;
}
public int getInningsPitched() {
return inningsPitched;
}
public void setInningsPitched(int aInningsPitched) {
inningsPitched = aInningsPitched;
}
public int getEarnedRuns() {
return earnedRuns;
}
public void setEarnedRuns(int aEarnedRuns) {
earnedRuns = aEarnedRuns;
}
public int getHits() {
return hits;
}
public void setHits(int aHits) {
hits = aHits;
}
public int getWalks() {
return walks;
}
public void setWalks(int aWalks) {
walks = aWalks;
}
#Override
public void loadData(Scanner input) {
super.loadData(input);
wins = input.nextInt();
saves = input.nextInt();
inningsPitched = input.nextInt();
earnedRuns = input.nextInt();
hits = input.nextInt();
walks = input.nextInt();
}
#Override
public String generateDisplayString() {
calculateERA();
calculateWHIP();
return String.format(super.generateDisplayString() + ", Wins:%1d, Saves:%1d,"
+ " ERA:%1.2f, WHIP:%1.3f ", wins, saves, ERA, WHIP);
}
public double calculateERA() {
try {
ERA = ((double)(earnedRuns * 9) / inningsPitched);
} catch (ArithmeticException e) {
ERA = 0;
}
return ERA;
}
public double calculateWHIP() {
try {
WHIP = ((double)(walks + hits) / inningsPitched);
} catch (ArithmeticException e) {
WHIP = 0;
}
return WHIP;
}
}
public class Batter extends Player {
private int atBats;
private int hits;
private int homeRuns;
private int rbi;
private int stolenBases;
private double batAvg;
Batter() {
super();
atBats = 0;
hits = 0;
homeRuns = 0;
rbi = 0;
stolenBases = 0;
}
public int getAtBats() {
return atBats;
}
public void setAtBats(int aAtBats) {
atBats = aAtBats;
}
public int getHits() {
return hits;
}
public void setHits(int aHits) {
hits = aHits;
}
public int getHomeRuns() {
return homeRuns;
}
public void setHomeRuns(int aHomeRuns) {
homeRuns = aHomeRuns;
}
public int getRbi() {
return rbi;
}
public void setRbi(int aRbi) {
rbi = aRbi;
}
public int getStolenBases() {
return stolenBases;
}
public void setStolenBases(int aStolenBases) {
stolenBases = aStolenBases;
}
#Override
public void loadData(Scanner input) {
super.loadData(input);
atBats = input.nextInt();
hits = input.nextInt();
homeRuns = input.nextInt();
rbi = input.nextInt();
stolenBases = input.nextInt();
}
#Override
public String generateDisplayString() {
calculateBattingAverage();
return String.format(super.generateDisplayString() +
", Batting Average:%1.3f, Home Runs:%1d, RBI:%1d, Stolen Bases:%1d"
, batAvg, homeRuns, rbi, stolenBases);
}
public double calculateBattingAverage() {
try{
batAvg = ((double)hits/atBats);
} catch (ArithmeticException e){
batAvg = 0;
}
return batAvg;
}
}
Also, its probably easy to tell I'm still fairly new here, because I just ran all my classes together in with the code sample and I can't figure out to add the gaps, so feel free to edit if need be.

The typical usage of instanceof in the type of scenario you're describing would be
if (foo instanceof FooSubclass) {
FooSubclass fooSub = (FooSubclass) foo;
//foo and fooSub now are references to the same object, and you can use fooSub to call methods on the subclass
} else if (foo instanceof OtherSubclass) {
OtherSubclass otherSub = (OtherSubclass) foo;
//you can now use otherSub to call subclass-specific methods on foo
}
This is called "casting" or "explicitly casting" foo to FooSubclass.

the concept to call the methods of your subclasses is called polymorphism.
In your runtime the most specific available method is called provided that the method names are the same.
so you can
Superclass class = new Subclass();
class.method();
and the method provided that overwrites the method in Superclass will be called, even if it's defined in the Subclass.
Sorry for my english, I hope that helps a little bit ;-)

What is wrong with my testing Player Class in Blackjack Java

I am trying to test my player class properly, I have almost done it but I am having issues with my p1.setPlayerHand method. This is the following code I have used for my player class:
Player Class:
package model;
public class Player
{
private String PlayerName;
private Hand PlayerHand;
private boolean Dealer;
public Player(String name)
{
PlayerName = name;
PlayerHand = new Hand();
Dealer = false;
}
public void setName (String name)
{
this.PlayerName = name;
}
public String getName()
{
return PlayerName;
}
public void setDealer (Boolean dealer)
{
this.Dealer = dealer;
}
public boolean getDealer()
{
return Dealer;
}
public void setPlayerHand (Hand hand)
{
this.PlayerHand = hand;
}
public void getHand()
{
PlayerHand.displayCardsinHand();
}
public static void main (String [] args)
{
Player p1 = new Player("player1");
Hand h = new Hand();
//System.out.println(p1);
p1.setName("BARRY");
System.out.println(p1.getName());
p1.setDealer(false);
System.out.println(p1.getDealer());
//this is the error that is preventing my program to run
p1.setPlayerHand(h.addCard(new Card(Suit.CLUBS, CardRank.ACE)));
p1.getHand();
}
}
The following error I receive (after testing the Player Class) is this:
Exception in thread "main" java.lang.Error: Unresolved compilation problem: The method setPlayerHand(Hand) in the type Player is not applicable for the arguments (void)
at model.Player.main(Player.java:57)
This is the Hand Class underneath (that is linked to the Player Class):
Hand Class:
package model;
import java.util.Vector;
import java.util.Random;
public class Hand
{
private Vector<Card> hand;
public Hand()
{
hand = new Vector<Card>();
}
public void addCard(Card c)
{
hand.add(c);
}
public void displayCardsinHand()
{
for (int card = 0; card < hand.size(); card++)
{
System.out.println(hand.elementAt(card));
}
}
public int getCardsinHand()
{
return hand.size();
}
public Card getCard(int position)
{
if(position >= 0 && position < hand.size())
return (Card)hand.elementAt(position);
else
return null;
}
public int getScore()
{
int value = 0;
boolean ace = false;
for (int i = 0; i < hand.size(); i++)
{
Card c;
c = getCard(i);
value = value + c.getRankValue();
if(c.getRankValue() == 1)
{
ace = true;
}
}
if(ace == true && value + 10 <= 21)
{
value = value + 10;
}
return value;
}
public static void main (String [] args)
{
Hand h = new Hand();
System.out.println(h);
h.displayCardsinHand();
System.out.println(h.getCardsinHand());
h.addCard(new Card(Suit.HEARTS, CardRank.ACE));
System.out.println(h.getCardsinHand());
h.addCard(new Card(Suit.SPADES, CardRank.JACK));
System.out.println(h.getCardsinHand());
h.addCard(new Card(Suit.DIAMONDS, CardRank.QUEEN));
System.out.println(h.getCardsinHand());
h.addCard(new Card(Suit.CLUBS, CardRank.KING));
System.out.println(h.getCardsinHand());
System.out.println(h.getCardsinHand());
h.displayCardsinHand();
h.getCard(1);
System.out.println(h.getScore());
}
}
I have tried modifying the p1.setPlayerHand testing numerous times. I appreciate any advice and tips on how to solve this issue, thank you.
If my code is too long for this post then I will gladly accept any advice on what I should do to cut it short (for future reference).
If anyone here required to see any other classes that I wrote (that may help them help me solve this error) then please notify me on here, thank you.

The method addCard doesn't return anything (void). So you can't pass the result of this method to setPlayerHand(Hand). That's what you're doing.

The code should compile and run if you change
p1.setPlayerHand(h.addCard(new Card(Suit.CLUBS, CardRank.ACE)));
to
h.addCard(new Card(Suit.CLUBS, CardRank.ACE));
p1.setPlayerHand(h);
This is because the setPlayerHand method needs to be passed an object of type Hand, but the addCard method doesn't return anything (it's declared as void).