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  • Why does Java ArrayList use per-element casting instead of per-array casting?

    - by user1111929
    What happens inside Java's ArrayList<T> (and probably many other classes) is that there is an internal Object[] array = new Object[n];, to which T Objects are written. Whenever an element is read from it, a cast return (T) array[i]; is done. So, a cast on every single read. I wonder why this is done. To me, it seems like they're just doing unnecessary casts. Wouldn't it be more logical and also slightly faster to just create a T[] array = (T[]) new Object[n]; and then just return array[i]; without cast? This is only one cast per array creation, which is usually far less than the number of reads. Why is their method to be preferred? I fail to see why my idea isn't strictly better?

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  • how to use an array list ?

    - by soad El-hayek
    salam 3lekom i need to know if i store my data in an Araaylist and i need to get the value that i've stroed in it for example : if i've an array list like this ArrayList A = new ArrayList(); A = {"Soad", "mahran"}; and i want to get each String lonly how can i do it ? I've tried to do it like this package arraylist; import java.util.ArrayList; public class Main { public static void main(String[] args) { ArrayList S = new ArrayList(); String A = "soad "; S.add(A); S.add("A"); String F = S.toString(); System.out.println(F); String [] W = F.split(","); for(int i=0 ; i<W.length ; i++) { System.out.println(W[i]); } } }

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  • Java: empty ArrayLists in a foor loop

    - by Patrick
    hi, I'm reusing the same ArrayList in a for loop, and I use for loop results = new ArrayList<Integer>(); experts = new ArrayList<Integer>(); output = new ArrayList<String>(); .... to create new ones. I guess this is wrong, because I'm allocating new memory. Is this correct ? If yes, how can I empty them ? Added: another example I'm creating new variables each time I call this method. Is this good practice ? I mean to create new precision, relevantFound.. etc ? Or should I declare them in my class, outside the method to not allocate more and more memory ? public static void computeMAP(ArrayList results, ArrayList experts) { //compute MAP double precision = 0; int relevantFound = 0; double sumprecision = 0; thanks

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  • Is it possible to use the values method for a HashMap if the values are ArrayLists?

    - by Denman
    I'm stuck trying to get something to work in an assignment. I have a HashMap<Integer, ArrayList<Object>> called sharedLocks and I want to check whether a certain value can be found in any ArrayList in the HashMap. The following code obviously wouldn't work because Object[] can't be cast to ArrayList[], but it is a demonstration of the general functionality that I want. ArrayList[] values = (ArrayList[]) sharedLocks.values().toArray(); boolean valueExists = false; for (int i = 0; i < values.length; i++) { if (values[i].contains(accessedObject)) { valueExists = true; } } Is there a way for me to check every ArrayList in the HashMap for a certain value? I'm not sure how to use the values method for HashMaps in this case. Any help would be much appreciated.

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  • how to pass arraylist as parameter to another screen

    - by user2867267
    how to pass arraylist as parameter to another activity in my condition im not using listview and checkif arraylist contain single element then pass that arrraylist as parameter toanother screen see thisline Category_name.get(position).toString()); how i remove position?? how to passs arraylist parameter toanother activity static ArrayList<Long> Menu_ID = new ArrayList<Long>(); static ArrayList<String> Category_name = new ArrayList<String>(); JSONArray school = json2.getJSONArray("data"); for (int i = 0; i < school.length(); i++) { JSONObject object = school.getJSONObject(i); Category_ID.add((long) i); Menu_ID.add(Long.parseLong(object.getString("menu_id"))); Category_name.add(object.getString("menu_title")); } Intent iMenuList = new Intent(MenuGroup.this, thirdstep.class); menuidvalue=""; menuidvalue =( Menu_ID.get(position)).toString(); iMenuList.putExtra("Menu_ID",menuidvalue); iMenuList.putExtra("menu_group", Category_name.get(position).toString()); startActivity(iMenuList);

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  • ArrayList of Entites Random Movement

    - by opiop65
    I have an arraylist of entites that I want to move randomly. No matter what I do, they won't move. Here is my female class: import java.awt.Graphics2D; import java.awt.Image; import java.awt.Rectangle; import java.util.Random; import javax.swing.ImageIcon; public class Female extends Entity { static int femaleX = 0; static int femaleY = 0; double walkSpeed = .1f; Random rand = new Random(); int random; int dir; Player player; public Female(int posX, int posY) { super(posX, posY); } public void update() { posX += femaleX; posY += femaleY; } public void draw(Graphics2D g2d) { g2d.drawImage(getFemaleImg(), posX, posY, null); if (Player.showBounds == true) { g2d.draw(getBounds()); } } public Image getFemaleImg() { ImageIcon ic = new ImageIcon("res/female.png"); return ic.getImage(); } public Rectangle getBounds() { return new Rectangle(posX, posY, getFemaleImg().getHeight(null), getFemaleImg().getWidth(null)); } public void moveFemale() { random = rand.nextInt(3); System.out.println(random); if (random == 0) { dir = 0; posX -= (int) walkSpeed; } } } And here is how I update the female class in the main class: public void actionPerformed(ActionEvent ae) { player.update(); for(int i = 0; i < females.size(); i++){ Female tempFemale = females.get(i); tempFemale.update(); } repaint(); } If I do something like this(in the female update method): public void update() { posX += femaleX; posY += femaleY; posX -= walkSpeed; } The characters move with no problem. Why is this?

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  • Dealing with ArrayLists in java...all members of the arraylist updating themselves?

    - by Charlie
    I have a function that shrinks the size of a "Food bank" (represented by a rectangle in my GUI) once some of the food has been taken. I have the following function check for this: public boolean tryToPickUpFood(Ant a) { int xCoord = a.getLocation().x; int yCoord = a.getLocation().y; for (int i = 0; i < foodPiles.size(); i++) { if (foodPiles.get(i).containsPoint(xCoord, yCoord)) { foodPiles.get(i).decreaseFood(); return true; } } return false; } Where decreaseFood shrinks the rectangle.. public void decreaseFood() { foodAmount -= 1; shrinkPile(); } private void shrinkPile() { WIDTH -=1; HEIGHT = WIDTH; } However, whenever one rectangle shrinks, ALL of the rectangles shrink. Why would this be?

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  • How to avoid null pointer error

    - by Jessy
    I trying to find whether the elements of 2 arrayLists are match or not. But this code give me error Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException since some of the elements are null. How can I solved this problem? String level []={"High","High","High","High","High","High"}; ArrayList<Object> n = new ArrayList<Object>(Arrays.asList(level)); String choice []={null,"High","Low","High",null,"Medium"}; ArrayList<Object> m = new ArrayList<Object>(Arrays.asList(choice)); //Check if the two arrayList are identical for(int i=0; i<m.size(); i++){ if(!(m.get(i).equals(n.get(i)))){ result= true; break; } } return result; }

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  • Java Memory Overhead

    - by flamealpha
    Hello, I would like to ask about Memory Overhead in java, I have a large ArrayList (61,770 items), and trying to calculate the amount of memory taken by each item (counting the object and its ArrayList entry), by profiling the app i get that after all the data is loaded, the heap takes ~ 25Mb. when the ArrayList has only 2 items the heap takes ~1Mb , so roughly: (24*1024*1024)/61,768 = 407 bytes. however, when i count the fields of the each object, i get 148 bytes(not including the ArrayList, and assuming int=4,float=4,reference=4), I am curious to know where did all of those extra bytes came from... i can guess that since the objects I store in the ArrayList are implementing an interface, they store extra values, maybe the VM stores a 4byte function pointer for each implemented method? the interface they implement have 20 functions so thats 80 more bytes, totaling 228 bytes, still not close to the 400 bytes measured. any help would be appreciated.

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  • nested iterator errors

    - by Sean
    //arrayList.h #include<iostream> #include<sstream> #include<string> #include<algorithm> #include<iterator> using namespace std; template<class T> class arrayList{ public: // constructor, copy constructor and destructor arrayList(int initialCapacity = 10); arrayList(const arrayList<T>&); ~arrayList() { delete[] element; } // ADT methods bool empty() const { return listSize == 0; } int size() const { return listSize; } T& get(int theIndex) const; int indexOf(const T& theElement) const; void erase(int theIndex); void insert(int theIndex, const T& theElement); void output(ostream& out) const; // additional method int capacity() const { return arrayLength; } void reverse(); // new defined // iterators to start and end of list class iterator; class seamlessPointer; seamlessPointer begin() { return seamlessPointer(element); } seamlessPointer end() { return seamlessPointer(element + listSize); } // iterator for arrayList class iterator { public: // typedefs required by C++ for a bidirectional iterator typedef bidirectional_iterator_tag iterator_category; typedef T value_type; typedef ptrdiff_t difference_type; typedef T* pointer; typedef T& reference; // constructor iterator(T* thePosition = 0) { position = thePosition; } // dereferencing operators T& operator*() const { return *position; } T* operator->() const { return position; } // increment iterator& operator++() // preincrement { ++position; return *this; } iterator operator++(int) // postincrement { iterator old = *this; ++position; return old; } // decrement iterator& operator--() // predecrement { --position; return *this; } iterator operator--(int) // postdecrement { iterator old = *this; --position; return old; } // equality testing bool operator!=(const iterator right) const { return position != right.position; } bool operator==(const iterator right) const { return position == right.position; } protected: T* position; }; // end of iterator class class seamlessPointer: public arrayList<T>::iterator { // constructor seamlessPointer(T *thePosition) { iterator::position = thePosition; } //arithmetic operators seamlessPointer & operator+(int n) { arrayList<T>::iterator::position += n; return *this; } seamlessPointer & operator+=(int n) { arrayList<T>::iterator::position += n; return *this; } seamlessPointer & operator-(int n) { arrayList<T>::iterator::position -= n; return *this; } seamlessPointer & operator-=(int n) { arrayList<T>::iterator::position -= n; return *this; } T& operator[](int n) { return arrayList<T>::iterator::position[n]; } bool operator<(seamlessPointer &rhs) { if(int(arrayList<T>::iterator::position - rhs.position) < 0) return true; return false; } bool operator<=(seamlessPointer & rhs) { if (int(arrayList<T>::iterator::position - rhs.position) <= 0) return true; return false; } bool operator >(seamlessPointer & rhs) { if (int(arrayList<T>::iterator::position - rhs.position) > 0) return true; return false; } bool operator >=(seamlessPointer &rhs) { if (int(arrayList<T>::iterator::position - rhs.position) >= 0) return true; return false; } }; protected: // additional members of arrayList void checkIndex(int theIndex) const; // throw illegalIndex if theIndex invalid T* element; // 1D array to hold list elements int arrayLength; // capacity of the 1D array int listSize; // number of elements in list }; #endif //main.cpp #include<iostream> #include"arrayList.h" #include<fstream> #include<algorithm> #include<string> using namespace std; bool compare_nocase (string first, string second) { unsigned int i=0; while ( (i<first.length()) && (i<second.length()) ) { if (tolower(first[i])<tolower(second[i])) return true; else if (tolower(first[i])>tolower(second[i])) return false; ++i; } if (first.length()<second.length()) return true; else return false; } int main() { ifstream fin; ofstream fout; string str; arrayList<string> dict; fin.open("dictionary"); if (!fin.good()) { cout << "Unable to open file" << endl; return 1; } int k=0; while(getline(fin,str)) { dict.insert(k,str); // cout<<dict.get(k)<<endl; k++; } //sort the array sort(dict.begin, dict.end(),compare_nocase); fout.open("sortedDictionary"); if (!fout.good()) { cout << "Cannot create file" << endl; return 1; } dict.output(fout); fin.close(); return 0; } Two errors are: ..\src\test.cpp: In function 'int main()': ..\src\test.cpp:50:44: error: no matching function for call to 'sort(<unresolved overloaded function type>, arrayList<std::basic_string<char> >::seamlessPointer, bool (&)(std::string, std::string))' ..\src\/arrayList.h: In member function 'arrayList<T>::seamlessPointer arrayList<T>::end() [with T = std::basic_string<char>]': ..\src\test.cpp:50:28: instantiated from here ..\src\/arrayList.h:114:3: error: 'arrayList<T>::seamlessPointer::seamlessPointer(T*) [with T = std::basic_string<char>]' is private ..\src\/arrayList.h:49:44: error: within this context Why do I get these errors? Update I add public: in the seamlessPointer class and change begin to begin() Then I got the following errors: ..\hw3prob2.cpp:50:46: instantiated from here c:\wascana\mingw\bin\../lib/gcc/mingw32/4.5.0/include/c++/bits/stl_algo.h:5250:4: error: no match for 'operator-' in '__last - __first' ..\/arrayList.h:129:21: note: candidate is: arrayList<T>::seamlessPointer& arrayList<T>::seamlessPointer::operator-(int) [with T = std::basic_string<char>, arrayList<T>::seamlessPointer = arrayList<std::basic_string<char> >::seamlessPointer] c:\wascana\mingw\bin\../lib/gcc/mingw32/4.5.0/include/c++/bits/stl_algo.h:5252:4: instantiated from 'void std::sort(_RAIter, _RAIter, _Compare) [with _RAIter = arrayList<std::basic_string<char> >::seamlessPointer, _Compare = bool (*)(std::basic_string<char>, std::basic_string<char>)]' ..\hw3prob2.cpp:50:46: instantiated from here c:\wascana\mingw\bin\../lib/gcc/mingw32/4.5.0/include/c++/bits/stl_algo.h:2190:7: error: no match for 'operator-' in '__last - __first' ..\/arrayList.h:129:21: note: candidate is: arrayList<T>::seamlessPointer& arrayList<T>::seamlessPointer::operator-(int) [with T = std::basic_string<char>, arrayList<T>::seamlessPointer = arrayList<std::basic_string<char> >::seamlessPointer] Then I add operator -() in the seamlessPointer class ptrdiff_t operator -(seamlessPointer &rhs) { return (arrayList<T>::iterator::position - rhs.position); } Then I compile successfully. But when I run it, I found memeory can not read error. I debug and step into and found the error happens in stl function template<typename _RandomAccessIterator, typename _Distance, typename _Tp, typename _Compare> void __adjust_heap(_RandomAccessIterator __first, _Distance __holeIndex, _Distance __len, _Tp __value, _Compare __comp) { const _Distance __topIndex = __holeIndex; _Distance __secondChild = __holeIndex; while (__secondChild < (__len - 1) / 2) { __secondChild = 2 * (__secondChild + 1); if (__comp(*(__first + __secondChild), *(__first + (__secondChild - 1)))) __secondChild--; *(__first + __holeIndex) = _GLIBCXX_MOVE(*(__first + __secondChild)); ////// stop here __holeIndex = __secondChild; } Of course, there must be something wrong with the customized operators of iterator. Does anyone know the possible reason? Thank you.

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  • using Object input\ output Streams with files and array list

    - by soad el-hayek
    hi every one .. i'm an it student , and it's time to finish my final project in java , i've faced too many problems , this one i couldn't solve it and i'm really ubset ! :S my code is like this : in Admin class : public ArrayList cos_info = new ArrayList(); public ArrayList cas_info = new ArrayList(); public int cos_count = 0 ; public int cas_count = 0 ; void coustmer_acount() throws FileNotFoundException, IOException{ String add=null; do{ person p = new person() ; cos_info.add(cos_count, p); cos_count ++ ; add =JOptionPane.showInputDialog("Do you want to add more coustmer..\n'y'foryes ..\n 'n'for No .."); } while(add.charAt(0) == 'Y'||add.charAt(0)=='y'); writenew_cos(); // add_acounts(); } void writenew_cos() throws IOException{ ObjectOutputStream aa = new ObjectOutputStream(new FileOutputStream("coustmer.txt")); aa.writeObject(cos_info); JOptionPane.showMessageDialog(null,"Added to file done sucessfuly.."); aa.close(); } in Coustmer class : void read_cos() throws IOException, ClassNotFoundException{ person p1= null ; int array_count = 0; ObjectInputStream d = new ObjectInputStream(new FileInputStream("coustmer.txt")); JOptionPane.showMessageDialog(null,d.available() ); for(int i = 0;d.available() == 0;i++){ a.add(array_count,(ArrayList) d.readObject()); array_count++; JOptionPane.showMessageDialog(null,"Haaaaai :D" ); JOptionPane.showMessageDialog(null,array_count ); } d.close(); JOptionPane.showMessageDialog(null,array_count +"1111" ); for(int i = 0 ; i it just print JOptionPane.showMessageDialog(null,d.available() ); and having excep. here a.add(array_count,(ArrayList) d.readObject()); p.s : person object from my own class and it's Serializabled

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  • ArrayList throwing exception on retrieval from google datastore (with gwt, java)

    - by sumeet
    I'm using Google Web Toolkit with java and google datastore as database. The entity class has arraylist and on trying to retrieve the data from data base I'm getting the exception: Type 'org.datanucleus.sco.backed.ArrayList' was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized. I'm using JPA. Entity code: package com.ver2.DY.client; import java.io.Serializable; import java.util.ArrayList; import javax.jdo.annotations.IdGeneratorStrategy; import javax.jdo.annotations.PersistenceCapable; import javax.jdo.annotations.Persistent; import javax.jdo.annotations.PrimaryKey; import com.google.gwt.user.client.rpc.IsSerializable; @PersistenceCapable public class ChatInfo implements Serializable, IsSerializable{ @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Long topicId; @Persistent private String chatTopic; @Persistent private ArrayList messages = new ArrayList(); @Persistent private boolean isFirstPost; public ChatInfo() { } public Long getTopicId() { return topicId; } public void setTopicId(Long topicId) { this.topicId = topicId; } public String getChatTopic() { return chatTopic; } public void setChatTopic(String chatTopic) { this.chatTopic = chatTopic; } public ArrayList getMessages() { return messages; } public void addMessage(String newMsg) { messages.add(newMsg); } public boolean isFirstPost() { return isFirstPost; } public void setFirstPost(boolean isFirstPost) { this.isFirstPost = isFirstPost; } } Method in db class: @Transactional public ChatInfo[] getAllChat() { PersistenceManager pm = PMF.get().getPersistenceManager(); List chats = null; ChatInfo[] infos = null; String query = "select from " + ChatInfo.class.getName(); try{ chats = (List) pm.newQuery(query).execute(); infos = new ChatInfo[chats.size()]; for(int i=0;i } It is a bit strange because earlier I was able to insert and retrieve the data but it now throwing an exception. On searching the web I could find that I need to convert the Arraylist from some DataNucleus type to java util but not sure how to do that.

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  • how to read data from file into array? java

    - by lox
    I need some help reading data from a txt file into my ArrayList. I know the code is pretty messy, but just try to take a look at it. The first part with the creating and putting the ArrayList into the txt file works perfectly. I just need some help at the end in the "marked" area. Sorry if I still have some words in my native language, but I didn't really had the time to translate everything. public class ContAngajat { String username; String password; } public class CreazaCont { // creating the arraylist and putting it into a file public static void ang(String args[]) { ArrayList<ContAngajat> angajati=new ArrayList<ContAngajat>(50); Scanner diskScanner = new Scanner(in); Scanner forn = new Scanner(in); int n; out.print("Introduceti numarul de conturi noi care doriti sa le introduceti: "); n=forn.nextInt(); out.println(); try{ FileWriter fw = new FileWriter("ConturiAngajati.txt", true); for(int i=0; i<n; i++){ ContAngajat cont = new ContAngajat(); out.print("Username: "); cont.username=diskScanner.nextLine(); out.print("Password: "); cont.password=diskScanner.nextLine(); angajati.add(cont); fw.write(cont.username + " "); fw.write(cont.password +"|"); } fw.close(); } catch(IOException ex){ System.out.println("Could not write to file"); System.exit(0); } for (int i=0; i<n; i++) { out.println("username: " + angajati.get(i).username + " password: " +angajati.get(i).password ); } } // HERE I'M TRING TO GET THE ARRAYLIST OUT OF THE FILE public static void RdAng(String args[]) { ArrayList<ContAngajat> angajati=new ArrayList<ContAngajat>(50); ContAngajat cont = new ContAngajat(); int count,i2,i; try{ FileReader fr = new FileReader("ConturiAngajati.txt"); BufferedReader br = new BufferedReader(fr); String line = ""; while((line=br.readLine())!=null) { String[] theline=line.split("|"); count=theline.length; for(i=0;i<theline.length;i++) { String[] theword = theline[i].split(" "); } } for(i2=0;i2<count;i2++) { ContAngajat contrd = new ContAngajat(); // "ERROR" OVER HERE for (int ird=0; ird <theword.length; ird++) { cont.username=theword[0]; cont.password=theword[1]; // they keep telling me "theword cannot be resolved" whenever i try to run this } angajati.add(contrd); } } catch(IOException ex){ System.out.println("Could not read to file"); System.exit(0); } } }

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  • Android How do i overwrite the filter for my ArrayAdapter?

    - by alan
    Hey guys my first post here... Im trying to write a custom filter to filter the arraylist in my arrayadapter such that my listview is filtered when i click on the button. For instance when i click on my button public void onClick(View arg0) { String abc = "abc"; m_adapter.getFilter().filter(abc); } However, when i click on my button, my app terminate unexpectedly. Here is my code for the arrayadapter and filter. Please help me. package com.ntu.rosemobile.searchlist; public class ResultsAdapter extends ArrayAdapter<SearchItem> implements Filterable{ public ArrayList<SearchItem> subItems; public ArrayList<SearchItem> allItems; private LayoutInflater inflater; private PTypeFilter filter; public ResultsAdapter(Context context, int textViewResourceId, ArrayList<SearchItem> items) { super(context, textViewResourceId, items); this.subItems = items; this.allItems = this.subItems; inflater= LayoutInflater.from(context); } @Override public Filter getFilter() { if (filter == null){ filter = new PTypeFilter(); } return filter; } //@Override public View getView(int position, View convertView, ViewGroup parent) { View v = convertView; if (v == null) { v = inflater.inflate(R.layout.listrow, null); } SearchItem o = subItems.get(position); if (o != null) { TextView pname = (TextView) v.findViewById(R.id.productname); TextView neg = (TextView) v.findViewById(R.id.negNum); TextView pos = (TextView) v.findViewById(R.id.posNum); TextView neu = (TextView) v.findViewById(R.id.neuNum); WebImageView productPhoto = (WebImageView)v.findViewById(R.id.pPhoto); if(productPhoto!=null){ productPhoto.setImageUrl(o.getImageUrl().toString()); productPhoto.loadImage(); } if(pname!= null){ pname.setText(o.getProductName().toString()); } if (neg != null) { String a = "" + o.getNegativeReviews(); neg.setText(a); } if(neu != null){ String a = "" + o.getNeutralReviews(); neu.setText(a); } if(pos != null){ String a = "" + o.getPositiveReviews(); pos.setText(a); } } return v; } private class PTypeFilter extends Filter{ @SuppressWarnings("unchecked") @Override protected void publishResults(CharSequence prefix, FilterResults results) { // NOTE: this function is *always* called from the UI thread. subItems = (ArrayList<SearchItem>)results.values; notifyDataSetChanged(); } @SuppressWarnings("unchecked") protected FilterResults performFiltering(CharSequence prefix) { // NOTE: this function is *always* called from a background thread, and // not the UI thread. FilterResults results = new FilterResults(); ArrayList<SearchItem> i = new ArrayList<SearchItem>(); if (prefix!= null && prefix.toString().length() > 0) { for (int index = 0; index < allItems.size(); index++) { SearchItem si = allItems.get(index); if(si.getPType().compareTo(prefix.toString()) == 0){ i.add(si); } } results.values = i; results.count = i.size(); } else{ synchronized (allItems){ results.values = allItems; results.count = allItems.size(); } } return results; } } }

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  • Using selection sort in java to sort floats

    - by user334046
    Hey, I need to sort an array list of class house by a float field in a certain range. This is my code for the selection sort: public ArrayList<House> sortPrice(ArrayList<House> x,float y, float z){ ArrayList<House> xcopy = new ArrayList<House>(); for(int i = 0; i<x.size(); i++){ if(x.get(i).myPriceIsLessThanOrEqualTo(z) && x.get(i).myPriceIsGreaterThanOrEqualTo(y)){ xcopy.add(x.get(i)); } } ArrayList<House> price= new ArrayList<House>(); while(xcopy.size()>0){ House min = xcopy.get(0); for(int i = 1; i < xcopy.size();i++){ House current = xcopy.get(i); if (current.myPriceIsGreaterThanOrEqualTo(min.getPrice())){ min = current; } } price.add(min); xcopy.remove(min); } return price; } Here is what the house class looks like: public class House { private int numBedRs; private int sqft; private float numBathRs; private float price; private static int idNumOfMostRecentHouse = 0; private int id; public House(int bed,int ft, float bath, float price){ sqft = ft; numBathRs = bath; numBedRs = bed; this.price = price; idNumOfMostRecentHouse++; id = idNumOfMostRecentHouse; } public boolean myPriceIsLessThanOrEqualTo(float y){ if(Math.abs(price - y)<0.000001){ return true; } return false; } public boolean myPriceIsGreaterThanOrEqualTo(float b){ if(Math.abs(b-price)>0.0000001){ return true; } return false; } When i call looking for houses in range 260000.50 to 300000 I only get houses that are at the top of the range even though I have a lower value at 270000. Can someone help?

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  • How to count occurrence of an element in a List

    - by MM
    I have an ArrayList a collection class of java as follows. ArrayList<String>animals = new ArrayList<String>(); animals.add("bat"); animals.add("owl"); animals.add("bat"); animals.add("bat"); As you can see the animals ArrayList consists of 3 bat elements and one owl element. I was wondering if there is any API in collection framework that returns the number of bat occurrences or is there a way to determine number of occurrences. I found that google's collection multiset does have an api that returns total number of occurrences of an element. But that is compatible only with jdk1.5. Our product is currently in jdk 1.6. Hence cannot use it.

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  • populate textarea from model arraylist

    - by user281180
    I have an arraylist namelist in my model and in my view I need to fill the textarea with the values in the arraylist {%> <%=Html.TextArea("Namelist",Html.Encode(namelist))%> <%} But i`m having the following in my textarea being dislpayed: System.Collections.ArrayList... How to solve this?

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  • How can I group an array of rectangles into "Islands" of connected regions?

    - by Eric
    The problem I have an array of java.awt.Rectangles. For those who are not familiar with this class, the important piece of information is that they provide an .intersects(Rectangle b) function. I would like to write a function that takes this array of Rectangles, and breaks it up into groups of connected rectangles. Lets say for example, that these are my rectangles (constructor takes the arguments x, y, width,height): Rectangle[] rects = new Rectangle[] { new Rectangle(0, 0, 4, 2), //A new Rectangle(1, 1, 2, 4), //B new Rectangle(0, 4, 8, 2), //C new Rectangle(6, 0, 2, 2) //D } A quick drawing shows that A intersects B and B intersects C. D intersects nothing. A tediously drawn piece of ascii art does the job too: +-------+ +---+ ¦A+---+ ¦ ¦ D ¦ +-+---+-+ +---+ ¦ B ¦ +-+---+---------+ ¦ +---+ C ¦ +---------------+ Therefore, the output of my function should be: new Rectangle[][]{ new Rectangle[] {A,B,C}, new Rectangle[] {D} } The failed code This was my attempt at solving the problem: public List<Rectangle> getIntersections(ArrayList<Rectangle> list, Rectangle r) { List<Rectangle> intersections = new ArrayList<Rectangle>(); for(Rectangle rect : list) { if(r.intersects(rect)) { list.remove(rect); intersections.add(rect); intersections.addAll(getIntersections(list, rect)); } } return intersections; } public List<List<Rectangle>> mergeIntersectingRects(Rectangle... rectArray) { List<Rectangle> allRects = new ArrayList<Rectangle>(rectArray); List<List<Rectangle>> groups = new ArrayList<ArrayList<Rectangle>>(); for(Rectangle rect : allRects) { allRects.remove(rect); ArrayList<Rectangle> group = getIntersections(allRects, rect); group.add(rect); groups.add(group); } return groups; } Unfortunately, there seems to be an infinite recursion loop going on here. My uneducated guess would be that java does not like me doing this: for(Rectangle rect : allRects) { allRects.remove(rect); //... } Can anyone shed some light on the issue?

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  • using Object input\ output Streams with files and array list

    - by soad el-hayek
    hi every one .. i'm an it student , and it's time to finish my final project in java , i've faced too many problems , this one i couldn't solve it and i'm really ubset ! :S my code is like this : in Admin class : public ArrayList cos_info = new ArrayList(); public ArrayList cas_info = new ArrayList(); public int cos_count = 0 ; public int cas_count = 0 ; void coustmer_acount() throws FileNotFoundException, IOException{ String add=null; do{ person p = new person() ; cos_info.add(cos_count, p); cos_count ++ ; add =JOptionPane.showInputDialog("Do you want to add more coustmer..\n'y'foryes ..\n 'n'for No .."); } while(add.charAt(0) == 'Y'||add.charAt(0)=='y'); writenew_cos(); // add_acounts(); } void writenew_cos() throws IOException{ ObjectOutputStream aa = new ObjectOutputStream(new FileOutputStream("coustmer.txt")); aa.writeObject(cos_info); JOptionPane.showMessageDialog(null,"Added to file done sucessfuly.."); aa.close(); } in Coustmer class : void read_cos() throws IOException, ClassNotFoundException{ person p1= null ; int array_count = 0; ObjectInputStream d = new ObjectInputStream(new FileInputStrea ("coustmer.txt")); JOptionPane.showMessageDialog(null,d.available() ); for(int i = 0;d.available() == 0;i++){ a.add(array_count,(ArrayList) d.readObject()); array_count++; JOptionPane.showMessageDialog(null,"Haaaaai :D" ); JOptionPane.showMessageDialog(null,array_count ); } d.close(); JOptionPane.showMessageDialog(null,array_count +"1111" ); for(int i = 0 ; i<a.size()&& found!= true ; i++){ count++ ; p1 =(person)a.get(i); user=p1.user; pass = p1.pass; cas_checkpass(); } } it just print JOptionPane.showMessageDialog(null,d.available() ); and having excep. here a.add(array_count,(ArrayList) d.readObject()); p.s : person object from my own class and it's Serializabled

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  • For-Each and Pointers in Java

    - by John
    Ok, so I'm tyring to iterate through an ArrayList and remove a specefic element. However, I am having some trouble using the For-Each like structure. When I run the following code: ArrayList<String> arr = new ArrayList<String>(); //... fill with some values (doesn't really matter) for(String t : arr) { t = " some other value "; //hoping this would change the actual array } for(String t : arr) { System.out.println(t); //however, I still get the same array here } My question in, how can I make 't' a pointer to 'arr' so that I am able to change the values in a for-each loop? I know I could loop through the ArrayList using a different structure, but this one looks so clean and readable, it would just be nice to be able to make 't' a pointer. All comments are appreciated! Even if you say I should just suck it up and use a different construct.

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  • Type mismatch: cannot convert from ArrayList<Data> to MyCollection

    - by Tommy
    I've read similar questions here but I'm still a little confused. MyCollection extends ArrayList<MyClass> MyClass implements Data yet this gives me the "cannot convert from ArrayList to MyCollection" MyCollection mycollection = somehandler.getCollection(); where getCollection looks like this public ArrayList<Data> getCollection() So my assumptions are obviously wrong. How can I make this work like I would like it to

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  • java - how to split string in to multiple parts?

    - by Ewen
    I have a string that contains a value "firstword second third", and an ArrayList. I want to split the whole string in to by spaces and add the splitted strings in to the ArrayList. For example,"firstword second third" can be split to three separate strings and added three times in to the ArrayList. "1 2 3 4" can be splitted in to 4 strings and added 4 times in to the ArrayList. See the code below: public void separateAndAdd(String notseparated) { for(int i=0;i<canBeSepartedinto(notseparated);i++{ //what should i put here in order to split the string via spaces? thearray.add(separatedstring); } } public int canBeSeparatedinto(String string) //what do i put here to find out the amount of spaces inside the string? return .... } Please leave a comment if you dont get what I mean or I should fix some errors in this post. Thanks for your time!

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  • How to return ArrayList results from an IntentService

    - by gcl1
    I have an IntentService that loads up an ArrayList with data from a network source (AWS SDB tables). The ArrayList is in a global space -- accessible to both the calling Activity and the IntentService (like this: appState = ((App)getApplicationContext())). When the IntentService is done, it notifies the Activity through a ResultReceiver, and the Activity calls adapter.notifyDataChanged() to update the ListView. This solution works most of the time, ... but it violates the rule that only the UI thread should make changes to data underlying a ListView. So as it is, I sometimes get an error: "The content of the adapter has changed but ListView did not receive a notification." I think this must be a common situation. Please let me know if you have any suggestions or best practices for this problem. Here are three options I'm aware of: Keep the IntentService, and have it store the results in another "working" ArrayList, also in the global space. When the result is ready, the IntentService calls the ResultReceiver (on the UI thread), which can then: a) copy the result to the ArrayList associated with the ListView, and b) call adapter.notifyDataChanged(). CONS: I don't like the idea of putting temp/working data in a global space, and copying the result list seems inefficient. Keep the IntentService, and have it pass the results back through a bundle loaded with a ParcelableArrayList. CONS: I'm not sure if this approach would scale for very large result sets. It also requires copying the result list. Switch to a Service which builds a local copy of the result list. Have the Activity directly access the address space of the Service in order to read the result list. CON: Still requires copying results to the ArrayList associated with the ListView. Thank you.

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  • how to display values of an arraylist defined in servlet using ajax call

    - by veena123
    can anyone please help me with below code servlet: below servlet is for statically defining an array. import java.io.; import javax.servlet.; import javax.servlet.http.; import java.util.; public class SampleAjax extends HttpServlet{ public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException,IOException { response.setContentType("text/html"); string plociyno = "abd1234"; PrintWriter pw = response.getWriter(); if (policyno.equals("abc1234")) { List dataList= new ArrayList(); dataList.add("automated refund possible"); request.setAttribute("data",dataList); RequestDispatcher dispatcher = request.getRequestDispatcher("refund.jsp"); if (dispatcher != null){ dispatcher.forward(request, response); } } } and my jsp: jsp for displayng the values of the arraylist in a table.... i want to do the same thing but using ajax.... please help <html <body><table id= "table" border="0" width="303"> <tr> <td width="250"><b>Your Policy Refund Details is:</b></td> </tr> <%Iterator itr; %> <% ArrayList refund= (ArrayList)request.getAttribute("data"); if(refund != null){ for(itr=refund.iterator(); itr.hasNext();){ %> <tr> <td><%=itr.next()%></td> </tr> <%}}%> </table> </body> </html> how can i display this arraylist values using ajax??? please help

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  • Trouble with arraylist and stack

    - by helloman
    I am having trouble starting out this program, I am suppose to write a program that will create an ArrayList, asking the user for 10 numbers. Then this will be put into the Array. Then after the list is made navigate it and if a number is even remove it from the ArrayList and copy it to a stack of integers. import java.io.* ; import java.util.*; public class Test { public static void main(String[] args){ Scanner input = new Scanner (System.in); ArrayList<Integer> integers = new ArrayList<Integer>(); System.out.print ("Enter Number: \n"); for (int i = 0; i < 10; i++){ integers.add(input.nextInt()); } for (int i = 0; i < 10 ; i++){ if (i %2==0) } } }

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