Develop Reference

Java - outOfMemory - Heap Space

So I'm trying to complete an exercise where I've been asked to implement a method that does a binary search in an ArrayList of objects. From the exercise:
Binary search
In the Main-class, implement a method public static int binarySearch(ArrayList<Book> books, int searchedId), which searches the list it received as a parameter, for a book with an id variable that matches the value of searchedId variable it received as a parameter. If that book is found the method, should return the index it's located at, in the list it received as a parameter. If the book isn't found, the method should return the value -1.
The method must be implemented as a binary search, which assumes the list is ordered. You should also assume, that the ids towards the beginning of the list, are always smaller than the ids towards the end of the list.
I have created two methods, one to check whether the arraylist is sorted (isItSorted) and the other one that will perform the binary search if the aforementioned method evaluates to true (binarySearch). Please see below:
public static boolean isItSorted(ArrayList<Book> books) {
ArrayList<String> boo = new ArrayList<>();
String isItSorted = "";
for (int i = 0; i < books.size(); i++) {
for (int j = i + 1; j < books.size(); j++) {
if (books.get(i).getId() < books.get(j).getId()) {
isItSorted = "true";
boo.add(isItSorted);
} else {
isItSorted = "false";
boo.add(isItSorted);
}
}
}
if (!(boo.contains("false"))) {
return true;
}
return false;
}
public static int binarySearch(ArrayList<Book> books, long searchedId) {
if (searchedId < 0 || books.isEmpty()) {
return -1;
} else if (isItSorted(books)) {
int start = 0;
int end = books.size() - 1;
int middle = (start + end) / 2;
if (books.get(middle).getId() == searchedId) {
return middle;
} else if (books.get(middle).getId() > searchedId) {
end = middle - 1;
} else if (books.get(middle).getId() < searchedId) {
start = middle + 1;
}
while (start <= end) {
if (books.get(start).getId() == searchedId) {
return start;
}
start++;
}
}
return -1;
}
Inside these java files, there's a test package that tests whether my solution is correct or not. While 95% of the tests are successful, when it reaches the method below (where it compares the time of execution compared to my other method (linear search)), I get the error Java outOfMemory heap Space.
I use NetBeans. I've already tried the JVM commands.
My solution seems to work with every number of objects I've tried, so perhaps there's something wrong with the test code below?
#Test
#Points("07-05.2")
public void binarySearchIsFasterThanLinearSearch() throws Throwable {
ArrayList<Book> books = generateBooks(10000);
Collections.sort(books, (k1, k2) -> k1.getId() - k2.getId());
int searched = 1000001;
long bSearchStart = System.nanoTime();
int binarySearchId = Searching.binarySearch(books, searched);
long bSearchEnd = System.nanoTime();
assertTrue("When binary search does not find what was searched for, it must return -1", binarySearchId == -1);
long lSearchStart = System.nanoTime();
int linearSearchId = Searching.linearSearch(books, searched);
long lSearchEnd = System.nanoTime();
assertTrue("When linear search does not find what was searched for, it must return -1", linearSearchId == -1);
long bSearchTime = bSearchEnd - bSearchStart;
long lSearchTime = lSearchEnd - lSearchStart;
assertTrue("When there are 10000 books to search, and the searched book is not found, binary search should be a lot faster than linear search. Current this isn't so", bSearchTime * 2 < lSearchTime);
}

ArrayList<String> boo = new ArrayList<>();
String isItSorted = "";
for (int i = 0; i < books.size(); i++) {
for (int j = i + 1; j < books.size(); j++) {
if (books.get(i).getId() < books.get(j).getId()) {
isItSorted = "true";
boo.add(isItSorted);
} else {
isItSorted = "false";
boo.add(isItSorted);
}
}
}
Adds on the order of 100 million items to the ArrayList boo.
If you want to check if something is sorted you can use much simpler code:
Book prev = books[0];
for (int i = 1; i < books.size(); i++) {
if (prev.getId() > books[i].getId())
return false;
}
return true;
But you shouldn't need to call it inside binarySearch() because that will defeat the purpose of binarySearch() and make it as slow as linearSearch().

how to input new string if there have value except zero

i need help. can somebody tell me about concept and example code i need use? the case is, I want input game history using java into mysql (phpmyadmin).
I'm already create like this if S0: 1.0; and all value zero
try
{
connection = dbManager.getConnection();
String bs = "S0:"+s[0]+"; S1:"+s[1]+"; S2:"+s[2]+"; S3:"+s[3]+"; S4:"+s[4]+"; S5:"+s[5]+"; S6:"+s[6]+"; S7:"+s[7]+"; S8:"+s[8]+"; S9:"+s[9]+"; S10:"+s[10]+"; S11:"+s[11]+"; S12:"+s[12]+"; S13:"+s[13]+"; S14:"+s[14]+"; S15:"+s[15]+"; S16:"+s[16]+"; S17:"+s[17]+"; S18:"+s[18]+"; S19:"+s[19]+"; S20:"+s[20]+"; S21:"+s[21]+"; S22:"+s[22]+"; S23:"+s[23]+"; S24:"+s[24]+"; S25:"+s[25]+"; S26:"+s[26]+"; S27:"+s[27]+"; S28:"+s[28]+"; S29:"+s[29]+"; S30:"+s[30]+"; S31:"+s[31]+"; S32:"+s[32]+"; S33:"+s[33]+"; S34:"+s[34]+"; S35:"+s[35]+"; S36:"+s[36]+"";
}
catch (SQLException e)
{
trace("player 1 update error");
}
and it's working and result like this
S0:1.0; S1:0.0; S2:0.0; S3:0.0; S4:0.0; S5:0.0; S6:0.0; S7:0.0; S8:0.0; S9:0.0; S10:0.0; S11:0.0; S12:0.0; S13:0.0; S14:0.0; S15:0.0; S16:0.0; S17:0.0; S18:0.0; S19:0.0; S20:0.0; S21:0.0; S22:0.0; S23:0.0; S24:0.0; S25:0.0; S26:0.0; S27:0.0; S28:0.0; S29:0.0; S30:0.0; S31:0.0; S32:0.0; S33:0.0; S34:0.0; S35:0.0; S36:0.0
but it's not efficient, the question is how i can input if there have any value except zero, example like S0:1 ; S1:0 ; S2:1 and insert into mysql just like this S0:1 ; S2:1 so if there no have value / zero, not being inserted. Thanks

You could try this:
String bs = "";
int count = 0;
for (int i = 0; i < size; i++) {
if(!s[i].equals(0.0)) {
if(count > 0) {
bs += " ; " ;
}
bs += "S" + count + ":" + s[i].split(".")[0];
count++;
}
}

try this code
private static String format (int x) {
if (x == 0) {
return null;
}
return String.format ("S%d = %d; ", x ,x);
}
// testing from main
{
StringBuilder buf = new StringBuilder();
for (int x = 0; x < 4; x++) { // dummy input stream
String rv = format (x);
if (rv != null) {
buf.append(rv);
}
}
System.out.println(buf.toString());
}

Group List with attribute and add another Attribute

I have a List of objects. I to assign a color to every object with a similar attibute ie.ParentId.I have done something like so:-
Map<String, String> idToColorMap = new HashMap<String, String>();
int colorIndex = 0;
for (int i = 0; i < myParentList.size(); i++)
{
if (myParentList.size() > 1 && !idToColorMap.containsKey(myParentList.get(i).getParentId())) {
Parent currentParent = myParentList.get(i);
currentParent.setColor(colorPallete[colorIndex]);
idToColorMap.put(currentParent.getParentId(), colorPallete[colorIndex]);
for (int j = i + 1; j < myFinalParentList.size(); j++) {
if (myParentList.get(j).getParentId().equals(currentParent.getParentId())) {
myParentList.get(j).setColor(colorPallete[colorIndex]);
}
}
if (++colorIndex == colorPallete.length) {
colorIndex = 0;
}
} else {
myParentList.get(0).setColor(colorPallete[0]);
idToColorMap.put(myParentList.get(0).getParentId(), colorPallete[0]);
}
}
But with this only the first item in the list with the ParentId is assigned the color and not all the items with the same ParentId

The problem comes from your tests.
// OK for parent[0] but not all other
if (myParentList.size() > 1 && !idToColorMap.containsKey(myParentList.get(i).getParentId())) {
...
}
// Will only set you first parent not all others
else {
myParentList.get(0).setColor(colorPallete[0]);
idToColorMap.put(myParentList.get(0).getParentId(), colorPallete[0]);
}
With your test you can only enter the if if you have not encounter this parentId. But if you have already encountered one then you go to else where you only change parent[0].
You should separate your test.
EDIT :
Here is something that should work (didn't test, maybe some minor correction has to be done). Plus: I didn't understand what is your myFinalParentList so I didn't put it in here. Just add your foreach after my code. if necessary
Map<String, String> idToColorMap = new HashMap<String, String>();
int colorIndex = 0;
String colorPallete = ...;
for (Parent parent : myParentList) {
// if is not in idIdColorMap then I add it
if (!idToColorMap.containsKey(parent.getParentId()) {
idToColorMap.put(parent.getParentId(), colorPallete[colorIndex]);
// increment colorIndex
if (colorIndex + 1 == colorPallete.length) {
colorIndex = 0;
} else {
colorIndex++;
}
}
// Set Parent's Color
parent.setColor(idToColorMap.get(parent.getId());
}

Saving Objects from an Iterated List

I'm currently workin' on a sales module using java+hibernate+oracle... I'm done with my order form in my jsp like this:
I'm getting my parameters doing this:
ArrayList<String> idMercaderias = new ArrayList<String>();
ArrayList<String> cantidades = new ArrayList<String>();
ArrayList<String> precios = new ArrayList<String>();
for (int k = 0; k < 10; k++) {
idMercaderias.add(request.getParameter("idMercaderia" + k));
cantidades.add(request.getParameter("cantidad" + k));
precios.add(request.getParameter("precio" + k));
}
I have 10 rows on my order detail, so I made the for, where my inputs are input1, input2, input3, etc. These are attributes of my object Mercaderia so i need to set them up, since they're on lists:
First I'm filtering the first list to avoid repeated articles:
Iterator itra = idMercaderias.listIterator();
ArrayList<String> sortedListIdMercaderias = new ArrayList<String>();
Object m;
while (itra.hasNext()) {
m = itra.next();
if (!sortedListIdMercaderias.contains(m)) {
sortedListIdMercaderias.add((String) m);
}
}
Now I create my object to set all the attributes:
DetallePedido detalle = new DetallePedido();
Now I'm doing a cycle 10 times (thinking of all rows in my form) and start to iterate each list to get my object attributes avoiding null or empty entries.
for (int x = 0; x < sortedListIdMercaderias.size(); x++) {
Iterator itr = idMercaderias.listIterator();
while (itr.hasNext()) {
String mercaderia = (String) itr.next();
if ((mercaderia != null) && (!mercaderia.equals(""))) {
Mercaderia mercaderiaSeleccionada = new MercaderiaDAO().findById(Integer.parseInt(mercaderia));
detalle.setMercaderia(mercaderiaSeleccionada);
}
}
Iterator itr2 = cantidades.listIterator();
while (itr2.hasNext()) {
String cantidad = (String) itr2.next();
if ((cantidad != null) && (!cantidad.equals(""))) {
int cantidadMercaderiaSeleccionada = Integer.parseInt(cantidad);
detalle.setCantidad(cantidadMercaderiaSeleccionada);
}
}
Iterator itr3 = precios.listIterator();
while (itr3.hasNext()) {
String precio = (String) itr3.next();
if ((precio != null) && (!precio.equals(""))) {
BigDecimal precioMercaderiaSeleccionada = new BigDecimal(precio);
detalle.setPrecioUnitario(precioMercaderiaSeleccionada);
}
}
Finally i just persist to my database:
Session session = new DetallePedidoDAO().getSession();
Transaction tx = session.beginTransaction();
try {
session.saveOrUpdate(detalle);
tx.commit();
session.close();
} catch (HibernateException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
I don't know why in the database i only get 1 row inserted (the last one with valid data) instead of all of them.
Any help will be really apreciated, this is for my final test in university project.

You've only ever got one DetallePedido object. You're changing its field values over and over in the various loops, but it's still just one object. Lastly you're saving it. Just once. Naturally, you only get one row inserted in your database.
What you could try is, instead of iterating through your Mercaderia objects, your Cantidad objects and your Precio objects separately; have a single loop that WITHIN EACH ITERATION creates a new DetallePedido object, sets the Mercaderia, the Cantidada and the Precio, and then saves the DetallePedido.

So, following the clues by David Wallace I made some tweaks to the idea and created an object WrapperDetallePedido like this:
public class WrapperDetallePedido {
int idMercaderia;
int cantidad;
double precio;
public int getIdMercaderia() {
return idMercaderia;
}
public void setIdMercaderia(int idMercaderia) {
this.idMercaderia = idMercaderia;
}
public int getCantidad() {
return cantidad;
}
public void setCantidad(int cantidad) {
this.cantidad = cantidad;
}
public double getPrecio() {
return precio;
}
public void setPrecio(double precio) {
this.precio = precio;
}
}
Then in my Controller I created a single ArrayList and set my DetallePedido attributes:
ArrayList<WrapperDetallePedido> listado = new ArrayList<WrapperDetallePedido>();
for (int k = 0; k < 10; k++) {
if (!request.getParameter("idMercaderia" + k).equals("")){
WrapperDetallePedido WDetallePedido = new WrapperDetallePedido();
WDetallePedido.setIdMercaderia(Integer.parseInt(request.getParameter("idMercaderia" + k)));
WDetallePedido.setCantidad(Integer.parseInt(request.getParameter("cantidad" + k)));
WDetallePedido.setPrecio(Double.parseDouble(request.getParameter("precio" + k)));
listado.add(WDetallePedido);
}
}
Finally used Iterator for the previous list and set all the items from listado and persist to the database:
for (Iterator iterador = listado.listIterator(); iterador.hasNext();) {
WrapperDetallePedido detalle = (WrapperDetallePedido) iterador.next();
Mercaderia mercaderiaSeleccionada = new MercaderiaDAO().findById(detalle.getIdMercaderia());
DetallePedido detallePedido = new DetallePedido();
detallePedido.setMercaderia(mercaderiaSeleccionada);
detallePedido.setCantidad(detalle.getCantidad());
detallePedido.setPrecioUnitario(new BigDecimal(detalle.getPrecio()));
detallePedido.setPedidos(pedidoGenerado);
Session session1 = new DetallePedidoDAO().getSession();
Transaction tx1 = session1.beginTransaction();
new DetallePedidoDAO().save(detallePedido);
try {
session1.saveOrUpdate(detallePedido);
tx1.commit();
session1.close();
} catch (HibernateException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
Finally got all my rows inserted as i needed... Thank you!

Why is this array giving a null pointer exception?

I'm trying to implement a dictionary with a hash table (not using Java's provided hash table classes, but rather made from scratch). Below is the find() method from my Dictionary class, used to detect whether or not a key is in the table when inserting/removing. If the key is already in the table, it returns a score associated with the key (elements in the table are inserted as pairs of key/score into LinkedLists in each table position). If not, it returns -1.
I am running a supplied test program to determine if my Dictionary class works, but I am encountering a NullPointerException when reaching a certain point. Included below is the particular test. Why would this exception be coming up? (I can provide more code if needed!)
Find:
public int find(String config) {
for (int i = 0; i < dictSize; i++) {
if (dict[i] != null) {
LinkedList<DictEntry> current = dict[i];
String currentConfig = current.peek().getConfig(); //Dictionary.java:66
if (currentConfig.equals(config)) {
int currentScore = current.peek().getScore();
return currentScore;
}
}
}
return -1;
}
Insert:
public int insert(DictEntry pair) throws DictionaryException {
String entryConfig = pair.getConfig();
int found = find(entryConfig); //Dictionary.java:27
if (found != -1) {
throw new DictionaryException("Pair already in dictionary.");
}
int entryPosition = hash(entryConfig);
if (dict[entryPosition] == null) { //Dictionary.java:35
LinkedList<DictEntry> list = new LinkedList<DictEntry>();
dict[entryPosition] = list;
list.add(pair);
return 0;
} else {
LinkedList<DictEntry> list = dict[entryPosition];
list.addLast(pair);
return 1;
}
}
The test:
// Test 7: insert 10000 different values into the Dictionary
// NOTE: Dictionary is of size 9901
try {
for (int i = 0; i < 10000; ++i) {
s = (new Integer(i)).toString();
for (int j = 0; j < 5; ++j) s += s;
collisions += dict.insert(new DictEntry(s,i)); //TestDict.java:69
}
System.out.println(" Test 7 succeeded");
} catch (DictionaryException e) {
System.out.println("***Test 7 failed");
}
Exception stack trace:
Exception in thread "main" java.lang.NullPointerException
at Dictionary.find(Dictionary.java:66)
at Dictionary.insert(Dictionary.java:27)
at TestDict.main(TestDict.java:69)

peek() returns null that's why. You can have a nullity check prior to getConfig() call.