Hoping for some help - I've been asked to write a hotel room system using methods for uni. All has been going well until I try to order the array alphabetically.
I have managed to get it to order within the method but it updated the main array (hotel). I want it to keep it within the order method, if that makes sense?
I've included a cut down version below without all the functions.
Currently it will reorder the array hotel so if you view the rooms the array will print like 'e,e,e,etc, George, Peter, Robert' instead of keeping its original form 'e, Robert, Peter, e,e,etc, George'
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
String roomName;
int roomNum = 0;
String[] hotelRef = new String[12];
String[] hotel = new String[12];
initialise(hotel); //initialise
while (roomNum < 13) {
System.out.println("Please select from the menu:");
System.out.println("V : View rooms");
System.out.println("O : Order Guests alphabetically");
String selection = input.next();
switch (selection) {
//There are more switch cases on the original version
case "O":
order(hotel);
break;
default:
System.out.println("");
}
}
}
private static void order(String[] hotelRef) {
int j;
boolean flag = true; //will determine when the sort is finished
String temp;
String[] order = new String[12];
order = hotelRef;
while (flag) {
flag = false;
for (j = 0; j < order.length - 1; j++) {
if (order[j].compareToIgnoreCase(order[j + 1]) > 0) {
//ascending sort
temp = order[j];
order[j] = order[j + 1]; // swapping
order[j + 1] = temp;
flag = true;
}
}
}
for (int y = 0; y < order.length; y++) {
if (!order[y].equals("e")) {
System.out.println("Room " + y + " is occupied by " + order[y]);
}
}
System.out.println("Ordering completed");
}
You should clone the hotelRef instead of assigning the reference like this order = hotelRef;
You could do the following while creating the order array :
String[] order = new String[hotelRef.length]; // to make sure that order has the right size.
and instead of order = hotelRef;
for (int i=0;i<order.length;i++)
order[i]=hotelRef[i]; // thereby cloning
or use System.arraycopy() or any other method to accomplish cloning the array.
You can make copy of hotel array in your order method:
String[] hotelCopy = new String[hotelRef.length];
System.arraycopy(hotelRef, 0, hotelCopy, 0, hotelRef.length);
And then just use hotelCopy inside your order method.
The problem lies with the following line
order = hotelRef;
Change it to
order = hotelRef.clone();
Though you are creating a new object, you have assigned the reference to outer object only. So whatever changes you make in the inner object it will be reflected to the outer object.
Related
The purpose of this project is to make a pokedex that adds and holds all the pokemon passed in by user input. When the user inputs a pokemon that is already stored in the pokedex the word "duplicate" is supposed to be printed to the console. The word duplicate is printed even though there are no actual duplicates within the object array. Here is my output from the console :
Welcome to your new PokeDex!
How many Pokemon are in your region?: 3
Your new Pokedex can hold 3 Pokemon. Let's start using it!
List Pokemon
Add Pokemon
Check a Pokemon's Stats
Sort Pokemon
Exit
What would you like to do? 2
Please enter the Pokemon's Species: red
Duplicate
Now here is all the code used that could possibly be making this error
import java.util.Scanner;
public class Project4 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.println("Welcome to your new PokeDex!");
System.out.print("How many Pokemon are in your region?: ");
int size = input.nextInt();
Pokedex pokedex = new Pokedex(size);
System.out.println("\nYour new Pokedex can hold " + size + " Pokemon. Let's start using it!");
int choice = 0;
boolean done = false;
while (!done) {
System.out.println("\n1. List Pokemon\n2. Add Pokemon\n3. Check a Pokemon's Stats" + "\n4. Sort Pokemon\n5. Exit");
System.out.print("\nWhat would you like to do? ");
choice = input.nextInt();
switch (choice) {
case 1:
String[] pokemonList = pokedex.listPokemon();
if (pokemonList == null)
System.out.println("Empty");
else
for (int i = 0; i < pokemonList.length; i++) {
System.out.println((i + 1) + ". " + pokemonList[i]);
}
break;
case 2:
System.out.print("\nPlease enter the Pokemon's Species: ");
String species = input.next();
pokedex.addPokemon(species);
break;
}
}
}
}
In the following class I have the actual method that adds the pokemon and the constructor for Pokedex
public class Pokedex {
Pokemon[] pokedex;
String pokeArray[];
public Pokedex(int size) {
pokedex = new Pokemon[size];
pokeArray = new String[size];
}
public boolean addPokemon(String species) {
Pokemon stuff = new Pokemon(species);
for (int i = 0; i < pokedex.length; i++) {
if (pokedex[i] == null) {
pokedex[i] = stuff;
}
else if (i < pokedex.length && pokedex[i] != null) {
System.out.println("Max");
}
if (pokedex[i].getSpecies().equalsIgnoreCase(species)) {
System.out.print("Duplicate");
break;
}
}
return false;
}
}
Sorry for the mass amounts of code I just need help tracing where this unexpected result is coming from.
The reason it's doing that is because of this bit of code here:
public boolean addPokemon(String species)
{
Pokemon stuff = new Pokemon(species);
for (int i = 0; i < pokedex.length; i++)
{
if (pokedex[i] == null)
pokedex[i] = stuff;
else if (i < pokedex.length && pokedex[i] !=null)
System.out.println("Max");
if(pokedex[i].getSpecies().equalsIgnoreCase(species))
{
System.out.print("Duplicate");
break;
}
}
return false;
}
The problem is just a little bit of syntax missing. In your for loop, you check to see if
A) there are any empty spots in the array
B) if every element in the array up to the user inputted size is full
and C) if any element in the array matches the one we're trying to add.
The problem you're encountering is because your C is an if instead of an else if. Because A sees the index is null, it assigns the new Pokemon to the Pokedex. Then because C is an if instead of an else if, it runs after you assign the new Pokemon and sees the Pokemon we just added and says it's a duplicate. Changing it to an else if would fix this.
Also, since there was no break; in A, it would assign every element of the array to the first one entered, causing any further additions to call Max. I edited the code and this is what I had that worked for me:
public boolean addPokemon(String species)
{
Pokemon stuff = new Pokemon(species);
for (int i = 0; i < pokedex.length; i++)
{
if(pokedex[i] !=null && pokedex[i].getSpecies().equalsIgnoreCase(species))
{
System.out.println("Duplicate");
break;
}
else if (pokedex[i] == null)
{
pokedex[i] = stuff;
break;
}
else if(i + 1 == pokedex.length)
{
System.out.println("Max");
break;
}
}
return false;
}
Also, out of curiosity, why is the addPokemon() function a boolean? You return a value (albeit arbitrarily) and then never do anything with that value. You could just make it a void, have it return nothing, and it would work just as fine.
I'm working on a something like music player. I'm building playlist on HashMap, I have a problem with deleting specific setlist(case 5). It works but when I delete position in the middle of the list case 1 (showing all playlists) no longer works because I have empty space (1,2,3,deleted,5,6....). Now how do I make those positions after deleted one decrease index by one? Looks like x-- doesn't solve my problem. I hope you understand my problem, here is the code, if you need me to translate anything to English just ask. Thanks for help!
package PLAYLIST2;
import java.util.HashMap;
import java.util.Scanner;
public class Odtwarzacz {
// String lista;
// Odtwarzacz(Playlist) {
// lista = b;
// }
public static void main(String[] args) {
int nr;
int koniec = 0;
String nazwa11;
int x = 0;
HashMap<Integer, Playlist> Playlista = new HashMap<Integer, Playlist>();
Playlista.put(x, new Playlist("Rock"));
x++;
Playlista.get(0).dodajUtwor("Stockholm Syndrome", "Muse", 2004);
Playlista.get(0).dodajUtwor("Absolution", "Muse", 2004);
Playlista.put(x, new Playlist("Pop"));
x++;
Scanner odczyt = new Scanner(System.in);
// TODO Auto-generated method stub
while (koniec == 0) {
System.out.println("_________________________");
System.out.println("1.Wyświetl listę playlist");
System.out.println("2.Dodaj playlistę");
System.out.println("3.Wyświetl playlistę");
System.out.println("4.Posortuj playlistę");
System.out.println("5.Usuń playlistę");
nr = odczyt.nextInt();
switch (nr) {
case 1: {
System.out.println("Lista playlist: ");
for (int i = 0; i < x; i++) {
System.out.println(i + ". " + Playlista.get(i).Nazwa());
}
break;
}
case 2: {
System.out.print("Podaj nazwę nowej playlisty: ");
nazwa11 = odczyt.next();
Playlista.put(x, new Playlist(nazwa11));
System.out.println("Dodano playlistę: "
+ Playlista.get(x).Nazwa());
x++;
break;
}
case 3: {
System.out.print("Podaj numer playlisty:");
nr = odczyt.nextInt();
Playlista.get(nr).wyswietlListe();
break;
}
case 4: {
System.out.print("Podaj numer playlisty:");
nr = odczyt.nextInt();
Playlista.get(nr).sortuj();
break;
}
case 5: {
System.out.print("Podaj numer playlisty:");
nr = odczyt.nextInt();
System.out.println("Skasowano playlistę: "
+ Playlista.get(nr).Nazwa());
Playlista.remove(nr);
x--;
break;
}
}
}
}
}
You do not seem to need a HashMap.
A HashMap is just a key-value store that has no order.
In your case, a List seems like a better choice. It comes with an order since it is the main point of it.
You can specifically use a ArrayList:
List<Playlist> playlists = new ArrayList<>();
playlists.add(new Playlist("Rock"));
// ...
Playlist p = playlists.get(index);
If you want to safely remove and get correct keys after, you must iterate the Map
int count = 0;
boolean found = false;
Iterator<Map.Entry<Integer,String>> iter = TestMap.entrySet().iterator();
while (iter.hasNext()) {
Map.Entry<Integer,String> entry = iter.next();
if("Sample".equalsIgnoreCase(entry.getValue())){
iter.remove();
found = true;
}
if (found) {
// set the new key using count...
}
count ++;
}
first let me see if i understand your problem correctly or not . you like to reoder playlist after any delete operation. 1,2,3,4,5 . you delete 3 , then it should be 1,2,4,5 and not 1,2, ,4,5.
if above is true , best is use linkedhashmap collection. also case1 you can rewrite as
case 1: {
System.out.println("Lista playlist: ");
for (Playlist pll:Playlista.values()) {
System.out.println(i + ". " + pll.Nazwa());
}
break;
}
This is a modified example from the book, Head First Java. It's a kind of Battleship game where a 3 element array is being used as the battleship. The user has to guess these 3 locations. Currently, I've hard-coded the values of the ship location to 2,3,4. When the user guesses the correct location "Hit" is printed. If not then "Miss" is printed. If a user guesses all 3 locations then "Kill" is printed. But I have a problem. Currently if the user enters the same location multiple times, it still gives a hit. I tried to fix this by changing the value of a variable that has already been hit (int cell) to "-1". But for some reason this didn't fix it too. Please tell me what I am doing wrong.
public class Game {
public static void main(String[] args) {
// TODO Auto-generated method stub
int [] location = {2,3,4};
SimpleDotCom firstGame = new SimpleDotCom();
firstGame.setLocation(location);
firstGame.checkYourself("2");
firstGame.checkYourself("2");
//firstGame.checkYourself("2");
}
}
public class SimpleDotCom {
int [] loc = null;
int numOfHits = 0;
void setLocation (int [] cellLocation){
loc = cellLocation;
}
void checkYourself(String userGuess){
int guess = Integer.parseInt(userGuess);
String result = "Miss";
for(int cell:loc){
if (guess == cell){
result = "Hit";
numOfHits++;
cell = -1;
break;
}
if (numOfHits==loc.length){
result = "Kill";
}
}
System.out.print("Result: " + result);
System.out.println(" ** Num of Hits: " + numOfHits);
}
}
When you loop over loc, you get an int cell for each location. The problem is that that variable doesn't have any connection to the array, it's only a copy. If you change it, nothing's going to happen to the original array. I suggest looping over loc with a traditional for(;;) and using the current array index within the loop's logic to set the right "cells" to -1.
because you are assigning -1 to local variable. not updating in array actually
for(int cell:loc){ // cell is local copy of element in array is you have array of primitive int
if (guess == cell){
result = "Hit";
numOfHits++;
cell = -1;
break;
}
if (numOfHits==loc.length){
result = "Kill";
}
}
You can use traditional for loop for this or use List which has methods for adding removing elements.
You need to update the array at the correct index, not simply change the value of the cell variable, which only references the array element at the current iteration state.
You should probably use a traditionnal for loop for that, since you cannot get the index for free from an enhanced for loop.
for (int i = 0; i < loc.length; i++) {
//code...
loc[i] = -1; //instead of cell = -1;
}
I'm trying to compress an array of objects that will have empty items interspersed with complete items. I want to put all the full elements at the start in the same order they started with, and the empty elements on the end.
The object in question uses a String field, "name", and an int field, "weight". An empty version has "no name" and 0 respectively. So an array of the type the method needs to deal with will contain something like:
Fred | 4
Bob | 3
no name | 0
Gina | 9
no name | 0
Yuki | 7
After feeding through the method, the array should go Fred, Bob, Gina, Yuki, no name, no name.
My thought for step one was to just figure out which were full and which weren't, so I came up with this:
public void consolidate() {
boolean[] fullSlots = new boolean[spaces.length];
// pass 1: find empties
for (int i = 0; i < spaces.length; i++) {
fullSlots[i] = spaces[i].getName().equals("no name");
}
}
spaces is the array of objects, getName() retrieves the name field from the object.
I'm not sure where to go from here. Suggestions?
EDIT: Okay, here's what Infested came up with:
public void consolidate()
{
int numberOfEmpties = 0, spacesLength = spaces.length;
Chicken[] spaces2 = new Chicken[spacesLength];
for(int i = 0; i < spaces.length; i++)
{
spaces2[i] = new Chicken(spaces[i].getName(),
spaces[i].getWeight());
}
// pass 1: find empties
for (int i = 0, j = 0; i < spacesLength; i++)
{
if (spaces2[i].getName().equals("no name") == false)
{
spaces[j] = new Chicken(spaces2[i].getName(),
spaces2[i].getWeight());
j++;
}
else
{
numberOfEmpties++;
}
}
for (int i = spacesLength - 1; numberOfEmpties > 0 ; numberOfEmpties--, i--)
{
spaces[i] = new Chicken("no name", 0);
}
}
Tested and working.
Java's Arrays.sort is stable, meaning that the relative order of equal elements is not going to change.
This sort is guaranteed to be stable: equal elements will not be reordered as a result of the sort.
You can use this property of the sorting algorithm to sort all your elements with a simple comparator:
Arrays.sort(
spaces
, new Comparator() {
public int compare(Object o1, Object o2) {
MyClass a = (MyClass)o1;
MyClass b = (MyClass)o2;
boolean aIsEmpty = "no name".equals(a.getName());
boolean bIsEmpty = "no name".equals(b.getName());
if (aIsEmpty && !bIsEmpty) {
return 1;
}
if (!aIsEmpty && bIsEmpty) {
return -1;
}
return 0;
}
}
);
This will sort all items with non-empty names ahead of the items with empty names, leaving the relative order of both groups of objects unchanged within their respective group.
If your space constraints allow you to create a new array of MyClass, you can go for a simpler algorithm: go through the original array once, and make a count of non-empty items. Then create a new array, and make two indexes: idxNonEmpty = 0, and idxEmpty = NonEmptyCount+1. Then go through the original array one more time, writing non-empty objects to idxNonEmpty++, and empty objects to idxEmpty++.
ill assume its a method of the class:
public void consolidate()
{
int lengthOfSpaces = spaces.length , i, numberOfEmpties = 0;
Type[] spacesNumberTwo = new Type[lengthOfSpaces ];
// pass 1: find empties
for (i = 0; i < lengthOfSpaces ; i++)
{
if(spaces[i].getName().equals("no name") == false)
spacesNumberTwo[i] = new Type(spaces[i].getName(), spaces[i].getInt());
else
numberOfEmpties++;
}
for (i = lengthOfSpaces - 1; numberOfEmpties > 0 ; numberOfEmpties--, i--)
{
spacesNumberTwo[i] = new Type("no name", 0);
}
spaces = spacesNumberTwo
}
Can someone could be kind and help me out here. Thanks in advance...
My code below outputs the string as duplicates. I don't want to use Sets or ArrayList. I am using java.util.Random. I am trying to write a code that checks if string has already been randomly outputted and if it does, then it won't display. Where I am going wrong and how do I fix this.
public class Worldcountries
{
private static Random nums = new Random();
private static String[] countries =
{
"America", "Candada", "Chile", "Argentina"
};
public static int Dice()
{
return (generator.nums.nextInt(6) + 1);
}
public String randomCounties()
{
String aTemp = " ";
int numOfTimes = Dice();
int dup = 0;
for(int i=0 ; i<numOfTimes; i++)
{
// I think it's in the if statement where I am going wrong.
if (!countries[i].equals(countries[i]))
{
i = i + 1;
}
else
{
dup--;
}
// and maybe here
aTemp = aTemp + countries[nums.nextInt(countries.length)];
aTemp = aTemp + ",";
}
return aTemp;
}
}
So the output I am getting (randomly) is, "America, America, Chile" when it should be "America, Chile".
When do you expect this to be false?
countries[i].equals(countries[i])
Edit:
Here's a skeleton solution. I'll leave filling in the helper methods to you.
public String[] countries;
public boolean contains(String[] arr, String value) {
//return true if value is already in arr, false otherwise
}
public String chooseRandomCountry() {
//chooses a random country from countries
}
//...
int diceRoll = rollDice();
String[] selection = new String[diceRoll];
for ( int i = 0; i < selection.length; i++ ) {
while (true) {
String randomCountry = chooseRandomCountry();
if ( !contains(selection, randomCountry ) {
selection[i] = randomCountry;
break;
}
}
}
//...then build the string here
This doesn't check important things like the number of unique countries.
You need a data structure which allows you to answer the question "does it already contain item X?"
Try the collection API, for example. In your case, a good candidate is either HashSet() or LinkedHashSet() (the latter preserves the insert order).
You'd probably be better of using another structure where you save the strings you have printed. Since you don't want to use a set you could use an array instead. Something like
/*
...
*/
bool[] printed = new bool[countries.length];
for(int i=0 ; i<numOfTimes ; /*noop*/ )
{
int r = nums.nextInt(countries.length);
if (printed[r] == false)
{
i = i + 1;
printed[r] = true;
aTemp = aTemp + countries[r];
aTemp = aTemp + ",";
}
}
return aTemp;
Consider what you're comparing it to:
if (!countries[i].equals(countries[i]))
are you comparing c[i] to c[i]? or c[i] to c[i-1]? Or do you need to check the whole array for a particular string? Perhaps you need a list of countries that get output.
make list uniqueCountries
for each string called country in countries
if country is not in uniqueCountries
add country to uniqueCountries
print each country in uniqueCountries
When you do this, watch out for index out of bounds, and adjust accordingly
Much faster way to do it then using HashSets and other creepy stuff. Takes less code too:
public String randomCounties() {
List<String> results = Arrays.asList(countries);
Collections.shuffle(results);
int numOfTimes = Dice();
String result = " ";
for(int i=0 ; i<numOfTimes; i++) {
result = result + countries[i] + ", ";
}
return result;
}
If you want to avoid outputting duplicate values, you need to record what values have already been listed or remove values from the pool of possibilities when they get selected.
You mention that you do not want to use Sets or ArrayList (I assume you mean Lists in general), I assume that is a requirement of the assignment. If so, you can accomplish this by building arrays and copying data between them the same way that an ArrayList would.
one note, your current implementation chooses between 1 and 6 entries from and array of 4 entries. If you force the selections to be unique you need to decide how to handle the case when you have no more unique selections.