I m using Arrays.binarysearch on a string array in an android app.
my array has 10 items, one of them being an UPPER CASE entry. Now, I can get index of all items from the array, except for the upper case one, which shows arrayIndexOutOfBound exception. For details: I m developing an android app with two activities. Activity A contains a list populated by an a string-array( called infections). When a user clicks an item on the list, he is taken to Activity B. The item clicked is sent to Activity B via putStringExtra method with the list's OnItemClickListener. In Activity B I am trying to get the received item's index on the same string-array (infections). All the other items work fine, except for one which is in UPPER case (the fifth item on the array... AIDS). Here are important snippets of my code:
strings.xml
<string-array name="infections">
<item>Acne vulgaris</item>
<item>Actinomycosis</item>
<item>Acute otitis media</item>
<item>African sleeping sickness</item>
<item>AIDS</item>
<item>Amebiasis</item>
<item>Anthrax</item>
</string-array>
ActivityA.java
String[] infections = getResources().getStringArray(R.array.all_inf);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
String clicked = adapter.getItem(position);
Intent i = new Intent(ActivityA.this, ActivityB.class);
i.putExtra(CLICKED_STRING,clicked);
startActivity(i);
}
});
ActivityB.java
String[] infections = getResources().getStringArray(R.array.all_inf);
String received = getIntent().getStringExtra(ActivityA.CLICKED_STRING);
int index = Arrays.binarySearch(infections,received);
When the item "AIDS" is clicked on the list, the app gives an arrayIndexOutOfBounds exception. when i replace "AIDS" with "Aids", the app works fine. Any help??
First of all, you need a sorted array for binarySearch().
Documentation:
public static int binarySearch (Object[] array, Object value)
Added in API level 1
Performs a binary search for value in the ascending sorted array
array. Searching in an unsorted array has an undefined result. It's
also undefined which element is found if there are multiple
occurrences of the same element.
Parameters
array the sorted array to search.
value the element to find.
Returns the non-negative index of the element, or a negative index
which is -index - 1 where the element would be inserted.
Without seeing your code, I assume you are trying to do something like this:
import java.util.Arrays;
public class BinarySearch
{
public static void main(String[] args)
{
String[] array = {"hello", "there", "YOU"};
Arrays.sort(array);
int index = Arrays.binarySearch(array, "you");
System.out.print(array[index]);
}
}
Which will give you this error:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -4
at BinarySearch.main(BinarySearch.java:18)
Basically, the element wasn't found, so it's returning a negative index as described in the documentation. Then if you try to access index -4 in your array, of course you get an index out of bounds exception.
So first of all, make sure that you don't access a negative index in your array.
Also, you could do something like this to check for the uppercase version if the lowercase version of a String doesn't exist in the array:
import java.util.Arrays;
public class BinarySearch
{
public static void main(String[] args)
{
String[] array = {"hello", "there", "YOU"};
Arrays.sort(array);
int index = Arrays.binarySearch(array, "you");
if (index < 0){
String str = "you";
index = Arrays.binarySearch(array, str.toUpperCase());
}
if (index >= 0){
System.out.print(array[index]);
}
}
}
Edited after comment:
It seems like this approach would be better for what you need, just go through the list using a for loop:
Keep your ActivityA code as it is in the question.
ActivityB:
String[] infections = getResources().getStringArray(R.array.all_inf);
String received = getIntent().getStringExtra(ActivityA.CLICKED_STRING);
int index = -1;
for (int i = 0; i < infections.length; i++){
if (received.equals(infections[i]){
index = i;
break;
}
}
if (index != -1){
//use index
}
Related
I'm adding three different objects to an ArrayList, but the list contains three copies of the last object I added.
For example:
for (Foo f : list) {
System.out.println(f.getValue());
}
Expected:
0
1
2
Actual:
2
2
2
What mistake have I made?
Note: this is designed to be a canonical Q&A for the numerous similar issues that arise on this site.
This problem has two typical causes:
Static fields used by the objects you stored in the list
Accidentally adding the same object to the list
Static Fields
If the objects in your list store data in static fields, each object in your list will appear to be the same because they hold the same values. Consider the class below:
public class Foo {
private static int value;
// ^^^^^^------------ - Here's the problem!
public Foo(int value) {
this.value = value;
}
public int getValue() {
return value;
}
}
In that example, there is only one int value which is shared between all instances of Foo because it is declared static. (See "Understanding Class Members" tutorial.)
If you add multiple Foo objects to a list using the code below, each instance will return 3 from a call to getValue():
for (int i = 0; i < 4; i++) {
list.add(new Foo(i));
}
The solution is simple - don't use the static keywords for fields in your class unless you actually want the values shared between every instance of that class.
Adding the Same Object
If you add a temporary variable to a list, you must create a new instance of the object you are adding, each time you loop. Consider the following erroneous code snippet:
List<Foo> list = new ArrayList<Foo>();
Foo tmp = new Foo();
for (int i = 0; i < 3; i++) {
tmp.setValue(i);
list.add(tmp);
}
Here, the tmp object was constructed outside the loop. As a result, the same object instance is being added to the list three times. The instance will hold the value 2, because that was the value passed during the last call to setValue().
To fix this, just move the object construction inside the loop:
List<Foo> list = new ArrayList<Foo>();
for (int i = 0; i < 3; i++) {
Foo tmp = new Foo(); // <-- fresh instance!
tmp.setValue(i);
list.add(tmp);
}
Your problem is with the type static which requires a new initialization every time a loop is iterated. If you are in a loop it is better to keep the concrete initialization inside the loop.
List<Object> objects = new ArrayList<>();
for (int i = 0; i < length_you_want; i++) {
SomeStaticClass myStaticObject = new SomeStaticClass();
myStaticObject.tag = i;
// Do stuff with myStaticObject
objects.add(myStaticClass);
}
Instead of:
List<Object> objects = new ArrayList<>();
SomeStaticClass myStaticObject = new SomeStaticClass();
for (int i = 0; i < length; i++) {
myStaticObject.tag = i;
// Do stuff with myStaticObject
objects.add(myStaticClass);
// This will duplicate the last item "length" times
}
Here tag is a variable in SomeStaticClass to check the validity of the above snippet; you can have some other implementation based on your use case.
Had the same trouble with the calendar instance.
Wrong code:
Calendar myCalendar = Calendar.getInstance();
for (int days = 0; days < daysPerWeek; days++) {
myCalendar.add(Calendar.DAY_OF_YEAR, 1);
// In the next line lies the error
Calendar newCal = myCalendar;
calendarList.add(newCal);
}
You have to create a NEW object of the calendar, which can be done with calendar.clone();
Calendar myCalendar = Calendar.getInstance();
for (int days = 0; days < daysPerWeek; days++) {
myCalendar.add(Calendar.DAY_OF_YEAR, 1);
// RIGHT WAY
Calendar newCal = (Calendar) myCalendar.clone();
calendarList.add(newCal);
}
Every time you add an object to an ArrayList, make sure you add a new object and not already used object. What is happening is that when you add the same 1 copy of object, that same object is added to different positions in an ArrayList. And when you make change to one, because the same copy is added over and over again, all the copies get affected.
For example,
Say you have an ArrayList like this:
ArrayList<Card> list = new ArrayList<Card>();
Card c = new Card();
Now if you add this Card c to list, it will be added no problem. It will be saved at location 0. But, when you save the same Card c in the list, it will be saved at location 1. So remember that you added same 1 object to two different locations in a list. Now if you make a change that Card object c, the objects in a list at location 0 and 1 will also reflect that change, because they are the same object.
One solution would be to make a constructor in Card class, that accepts another Card object. Then in that constructor, you can set the properties like this:
public Card(Card c){
this.property1 = c.getProperty1();
this.property2 = c.getProperty2();
... //add all the properties that you have in this class Card this way
}
And lets say you have the same 1 copy of Card, so at the time of adding a new object, you can do this:
list.add(new Card(nameOfTheCardObjectThatYouWantADifferentCopyOf));
It can also consequence of using the same reference instead of using a new one.
List<Foo> list = new ArrayList<Foo>();
setdata();
......
public void setdata(int i) {
Foo temp = new Foo();
tmp.setValue(i);
list.add(tmp);
}
Instead of:
List<Foo> list = new ArrayList<Foo>();
Foo temp = new Foo();
setdata();
......
public void setdata(int i) {
tmp.setValue(i);
list.add(tmp);
}
I have 2 APIs. From API1 I'm fetching a list of category names and setting it on spinner. From API2 I'm getting a category name, which I want to set as selected item in the spinner. But the problem is that the first time I'm not getting any position. When I go back to previous activity and come back to my activity, this time I'm getting the position.
private int getIndex(Spinner spinner, String myString){
int index = 0;
for (int i=0;i<spinner.getCount();i++){
if (spinner.getItemAtPosition(i).equals(myString)){
index = i;
}
}
return index;
}
// API2's JSON parsing
if(newobj.getString("cat_name")!=null){
int spinnerPosition = getIndex(catspin, newobj.getString("cat_name"));
catspin.setSelection(spinnerPosition);
}
How to make a 'random call' name in List in database sqlite. How can I call one by one without repeating its value. My layout is one textview, If I click the name it will change. Thank you.
Untested, but should be fine:
Query your database, then use the returned Cursor to populate a LinkedList with whatever options you would like.
LinkedList list = new LinkedList();
if (cursor.getCount() > 0) {
for (int i = 0; i < cursor.getCount(); i++) {
cursor.moveToPosition(i);
list.add(cursor.getString(etc...);
}
}
Create a Random object, and use it to select and remove a random element from list each time:
Random rnd = new Random();
//The below section could be repeated on, for instance, a button click.
int randomValue = rnd.nextInt(list.size());
String result = list.get(randomValue);
list.remove(randomValue);
Each time an element is removed, the LinkedList will adjust in size to accommodate it, so no results will be repeated.
#PPartisan not working.
I add button to test the result from textview. 1 row only detected when I pressed back and back to activity the result is the same value. I clicked the button did not work.
rnd = new Random();
randomValue = rnd.nextInt(list.size());
result =list.get(randomValue).toString();
list.remove(randomValue);
btnClick.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v){
tv.setText(result);
}
});
I searched for related questions but didn´t find a solution (at least i don´t know if i named it correctly)
So, i have two ArrayLists and i would like to randomize all of them to get a value:
public class ListBox {
public static ArrayList listOne(){
ArrayList<Lists> listOne = new ArrayList<>();
listOne.add(new Item("Text One"));
listOne.add(new Item("Text Two"));
return listOne;
}
public static ArrayList listTwo(){
ArrayList<Lists> listTwo = new ArrayList<>();
listTwo.add(new Item("Text Three"));
listTwo.add(new Item("Text Four"));
return listTwo;
}
}
in other activity:
public void buttonClick(View view){
ArrayList<Lists> algumasListas = ListBox.listOne();
...
}
This is where i shuffle it
public class ListMixer extends ListBox{
public ArrayList<Lists> listas = null;
public ListMixer(ArrayList<Lists> listas ) {
this.listas = listas;
}
protected String mixList(){
Double randomNumber = new Double(Math.random() * listas.size());
int randomNum = randomNumber.intValue();
Lista lista= listas.get(randomNum);
String listaString2 = String.valueOf(lista);
String message = ("This is your list: " + listas);
return message;
}
}
my desired output would be one of the four listItems.
Appreciate the help!
Merge arrays into single one of size N.
Choose a random number in range 0..N-1.
Choose an element by index.
The first bug I'm seeing in your code is that listOne() returns object listTwo when called, which doesn't exist. It probably shouldn't even compile, unless something funky is going on with global scope variables.
The following code should do what you want by merging the two lists into one and then returning a random object from them.
public Object randomFromList(List<Object> listOne, List<Object> listTwo){
List<Object> bigList = new ArrayList<Object>(listOne.size() + listTwo.size());
bigList.addAll(listOne);
bigList.addAll(listTwo);
return bigList.get(new Random().nextInt(bigList.size()));
}
For optimization, if you call this a lot, I would save the Random() object outside of the method to avoid instantiating it every time you make the call.
I am working on an application for Android. For this I am making an Activity in which you select your country and then a spot in that country. I have one spinner that contains a list of all available countries. Now, what I want it to do is get the country that has been selected, then filter a list of spots that I have for the items that start with the country that has been selected. Then it should put the spots for the selected country into a different spinner. Just for clarity, the list of countries is just a list of countries, and the list of spots looks like:
Country1 - Spot1
Country1 - Spot2
Country2 - Spot1
Country2 - Spot2
And so on.
This is what I thought the code should work like:
Get selected country from spinner 1.
Make a new ArrayList containing the spots.
Make a second empty ArrayList.
For each entry of the ArrayList containing the spots, check if it starts with the selected country.
If so, add it to the second ArrayList.
Once this is all done, make an ArrayAdapter with the second ArrayList.
Set this ArrayAdapter for spinner 2.
I tried to achieve this with the following code:
public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {
String selectedCountry = parent.getItemAtPosition(pos).toString();
ArrayList<CharSequence> arraylist = new ArrayList<CharSequence>();
arraylist.addAll(R.array.spots_array);
ArrayList<CharSequence> arraylist2 = new ArrayList<CharSequence>();
for (i=0; i<arraylist.size(); i++) {
String delimiter = " - ";
if ((arraylist(i).split(delimiter)).equals(selectedCountry)) {
arraylist2.add(arraylist(i).string.substring(string.lastIndexOf('-') + 1));
}
}
ArrayAdapter<CharSequence> arrayAdapter2 = ArrayAdapter.createFromResource(this, arraylist2<CharSequence>, android.R.layout.simple_spinner_item);
arrayAdapter2.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner2.setAdapter(arrayAdapter2);
spinner2.setOnItemSelectedListener(this);
}
But it gives several errors:
At addAll() it says: "The method addAll(int, Collection) in the type ArrayList is not applicable for the arguments (int)"
At arraylist it says: "The method arraylist(int) is undefined for the type Configuration"
At string (inside substring) it says: "string cannot be resolved"
I am still relatively new to Android, and am having a lot of trouble getting this working. Can anybody please help me out?
There is a lot of little mistakes in your code :
To access an element in an arraylist use the get(position) method
When you add your "spot_array", you actually add the id of the resource, not the array itself (see here)
Here is your code updated, it should works or may need some tweaks
public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {
String selectedCountry = parent.getItemAtPosition(pos).toString();
List<CharSequence> arraylist = new ArrayList<CharSequence>();
arraylist.addAll(Arrays.asList(getResources().getTextArray(R.array.spots_array)));
List<CharSequence> arraylist2 = new ArrayList<CharSequence>();
String delimiter = " - ";
for (int i=0; i<arraylist.size(); i++) {
String country = arraylist.get(i).toString();
if (country.contains(selectedCountry)) {
arraylist2.add(country.substring(country.lastIndexOf('-') + 2));
}
}
ArrayAdapter<CharSequence> arrayAdapter2 = ArrayAdapter.createFromResource(this, android.R.id.text1, android.R.layout.simple_spinner_item);
arrayAdapter2.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner2.setAdapter(arrayAdapter2);
spinner2.setOnItemSelectedListener(this);
}
You have several errors in your code.
Firstly, the method addAll of the ArrayList must take as an argument a Collection. You are passing an Android array id R.array.spots_array; bear in mind that the Android ids are integers.
The usually method to fetch a string array from Android resources is (inside an activity):
String[] myArray = getResources().getStringArray(R.array.spots_array);
Second error: you should access the ArrayList elements by calling the method get(position) , not directly (arraylist(position)). Something like arraylist.get(position).
Third error:
arraylist2.add(arraylist(i).string.substring(string.lastIndexOf('-') + 1));
should simply be arraylist2.add(arraylist.get(i)); for adding one list element to another.
More on ArrayLists can be found here.