I know the title doesn't say much, but I have a pretty specific problem that is difficult to describe:
I'm making an android app with Android Studio, and for one activity I have a list where the values that are stored in a json file will go.
For getting these values I use another class with a get() method which returns the values in an arraylist. The problem is that the IDE says 2 contrary statements: in the activity class it says that the get() method has to be static and in the other class it says that the get() method can't be static.
This is the code:
CompanySelector.java (the activity)
public class CompanySelector extends AppCompatActivity {
ArrayList<String> companyList = CompanyStorage.get();
}
==> here it gives an error in CompanyStorage.get() and says that get() should be static.
CompanyStorage.java (the other class)
abstract class CompanyStorage extends Context {
private ArrayList<String> companyList;
protected CompanyStorage() throws JSONException {
companyList = get();
}
ArrayList<String> get() throws JSONException {
JSONObject companyData = new JSONObject();
ArrayList<String> companyList = new ArrayList<>();
// Open data.json and convert to JSONObject
String json = OpenFileAsString("data.json");
try {
companyData = new JSONObject(json);
} catch (JSONException e) {
e.printStackTrace();
}
// return json array as ArrayList
if (companyData.getJSONArray("companies") != null) {
for (int i=0;i<companyData.getJSONArray("companies").length();i++){
companyList.add(companyData.getJSONArray("companies").getString(i));
}
}
return companyList;
}
public String OpenFileAsString(String filename) {
try {
InputStream stream = getAssets().open( filename );
int size = stream.available();
byte[] bytes = new byte[size];
stream.read(bytes);
stream.close();
return new String( bytes );
} catch ( IOException e ) {
Log.i("GuiFormData", "IOException: " + e.getMessage() );
}
return null;
}
}
==> Here it says that if get() is static, OpenFileAsString() should also be static, but then it gives an error, because getAssets() can't be in a static method.
Does anyone know what I should do? I'm fairly new to Java and application design..
Try to put static at the get() and OpenFileAsString(String filename) methods header and use context.getAssets() instead of getAssets()
Related
Here's my method where im reading json file.
private void LoadTabaksFromJson() {
InputStream raw = mContext.getResources().openRawResource(R.raw.tabaks);
Reader reader = new BufferedReader(new InputStreamReader(raw));
ListOfTabaks listOfTodos = new Gson().fromJson(reader, ListOfTabaks.class);
List<Tabak> todoList = listOfTodos.getTodoArrayList();
for (Tabak item: todoList){
mDataBase.insert(TabakTable.NAME,null,getContentValues(item));
}
}
public class ListOfTabaks {
protected ArrayList<Tabak> tabakArrayList;
public ArrayList<Tabak> getTodoArrayList(){
return tabakArrayList;
}
}
And Exeption
Caused by: java.lang.NullPointerException: Attempt to invoke interface
method 'java.util.Iterator java.util.List.iterator()' on a null object
reference
at
com.hookah.roma.hookahmix.TabakLab.LoadTabaksFromJson(TabakLab.java:61)
at com.hookah.roma.hookahmix.TabakLab.(TabakLab.java:32)
at com.hookah.roma.hookahmix.TabakLab.get(TabakLab.java:37)
at
com.hookah.roma.hookahmix.TabakListFragment.updateUI(TabakListFragment.java:38)
at
com.hookah.roma.hookahmix.TabakListFragment.onCreateView(TabakListFragment.java:32)
at
android.support.v4.app.Fragment.performCreateView(Fragment.java:2184)
at
android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1298)
at
android.support.v4.app.FragmentManagerImpl.moveFragmentsToInvisible(FragmentManager.java:2323)
at
android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2136)
And json file :
{
"tabaksArrayList":[
{
"name":"Абрикос",
"description":"Со вкусом Абрикоса",
"rating":"4.1",
"favourite":"1",
"family":"Al fakher"
},
{
"name":"Ананас",
"description":"Со вкусом Ананаса",
"rating":"4.1",
"favourite":"1",
"family":"Al fakher"
},
{
"name":"Апельсин",
"description":"Со вкусом Апельсина",
"rating":"4.1",
"favourite":"1",
"family":"Al fakher"
},
{
"name":"Апельсин с мятой",
"description":"Со вкусом Апельсина с мятой",
"rating":"4.1",
"favourite":"1",
"family":"Al fakher"
},
It looks like your json schema issue, i'm guessing listOfTodos return null. You can refer to this to generate your schema.
But sometimes that tools can make us confuse so i tried to create your schema manually like this:
TabakRoot.java
public class TabakRoot {
#SerializedName("tabaksArrayList")
private List<TabakItem> tabakItem = null;
public List<TabakItem> getTabakItem() {
return tabakItem;
}}
TabakItem.java
public class TabakItem {
#SerializedName("family")
#Expose
private String tabakFamily;
public String getTabakFamily() {
return tabakFamily;
}}
finally
TabakRoot listOfTodos = new Gson().fromJson(reader, TabakRoot.class);
List<TabakItem> todoList = listOfTodos.getTabakItem();
Looks like you are not initialising your ArrayList, try changing:
protected ArrayList<Tabak> tabakArrayList;
for:
protected ArrayList<Tabak> tabakArrayList = new ArrayList<>();
Please put your json file in assets folder
use AsyncTask to protect from ANR like situtation
onBackground(){
String json = null;
try {
InputStream stream = activity.getAssets().open("ur_json_file_in_assets_folder.json");
int size = stream.available();
byte[] buffer = new byte[size];
stream.read(buffer);
stream.close();
json = new String(buffer, "UTF-8");
} catch (IOException e) {
e.printStackTrace();
return null;
}
return json;
}
then parse in
onPostExecute(String str){
JsonObject object = new JsonObject(str);
JsonArray arr = object.getJsonArray("tabaksArrayList");
...}
more details at ParseJsonFileAsync.java
You're not initialising tabakArrayList, add a constructor to your ListOfTabaks as following
public ListOfTabaks{
tabakArrayList = new ArrayList<>();
}
and you should be fine
I've got this code with fetches the "rate" data from an API, along with "rate", I need to get the "name". If I get "name" it often binds it below the "rate".
I need it to join on the same row of the List View, so it is like [Rate Name].
I need to get two objects of a JSON Array and bind it to the array adapter so I can display two objects in the same row of a List View so it is more user friendly.
The code below is of the AsyncTask, the code works fine but I need to add one more object and make sure it is displayed as one rate - one name and then iterating through the loop and adding more as needed in the same order.
public class AsyncTaskParseJson extends AsyncTask<String, String, String> {
// the url of the web service to call
String yourServiceUrl = "eg: URL";
#Override
protected void onPreExecute() {
}
String filename = "bitData";
#Override
protected String doInBackground(String... arg0) {
try {
// create new instance of the httpConnect class
httpConnect jParser = new httpConnect();
// get json string from service url
String json = jParser.getJSONFromUrl(yourServiceUrl);
// parse returned json string into json array
JSONArray jsonArray = new JSONArray(json);
// loop through json array and add each currency to item in arrayList
//Custom Loop Initialise
for (int i = 1; i < 8; i++) {
JSONObject json_message = jsonArray.getJSONObject(i);
// The second JSONObject which needs to be added
JSONObject json_name = jsonArray.getJSONObject(i);
if (json_message != null) {
//add each currency to ArrayList as an item
items.add(json_message.getString("rate"));
String bitData = json_message.getString("rate");
String writeData = bitData + ',' +'\n';
FileOutputStream outputStream;
File file = getFileStreamPath(filename);
// first check if file exists, if not create it
if (file == null || !file.exists()) {
try {
outputStream = openFileOutput(filename, MODE_PRIVATE);
outputStream.write(writeData.getBytes());
outputStream.write("\r\n".getBytes());
outputStream.close();
} catch (Exception e) {
e.printStackTrace();
}
}
// if file already exists then append bit data to it
else if (file.exists()) {
try {
outputStream = openFileOutput(filename, Context.MODE_APPEND);
outputStream.write(writeData.getBytes());
outputStream.write("\r\n".getBytes());
outputStream.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
// below method will run when service HTTP request is complete, will then bind text in arrayList to ListView
#Override
protected void onPostExecute(String strFromDoInBg) {
ListView list = (ListView) findViewById(R.id.rateView);
ArrayAdapter<String> rateArrayAdapter = new ArrayAdapter<String>(BitRates.this, android.R.layout.simple_expandable_list_item_1, items);
list.setAdapter(rateArrayAdapter);
}
}
Just Create Custom Class Messsage:
public class Item{
private String name;
private String rate;
public void Message(String n, String r){
this.name=n;
this.rate=r;
}
// create here getter and setter
}
Now in your background, you have to add name and rate in Message class
Public class MainAcitity extends Activity{
public static List<Item> items= new ArrayList<>();// define in inside the class
// this has to be down on background
Item i=new Item(json_message.getString("name"),json_message.getString("rate"));
items.add(i);
Now pass this listmessge onPostExecute :
ListView list = (ListView) findViewById(R.id.rateView);
ArrayAdapter<String> rateArrayAdapter = new ArrayAdapter<String>(BitRates.this, android.R.layout.simple_expandable_list_item_1, items);
list.setAdapter(rateArrayAdapter);
Is that any helpful for you.
Follow this link.You will get my point.
https://devtut.wordpress.com/2011/06/09/custom-arrayadapter-for-a-listview-android/
quick question about creating objects when given a Class object. Or maybe I need to go about this differently. First off my plan, I am writing a method that will take an array of File objects, and read each one into a Set, where each set is then appended to a list and the list returned. Below is what I have:
private static List<Set<String>> loadFiles(File[] files, Class whatType, Charset charSet){
List<Set<String>> setList = new ArrayList<Set<String>>(files.length);
try {
for(File f : files){
BufferedInputStream bs = new BufferedInputStream(new FileInputStream(f));
InputStreamReader r = new InputStreamReader(bs, charSet);
BufferedReader br = new BufferedReader(r);
Set<String> set = new HashSet<>(); //This is the problem line
String line = null;
while( (line = br.readLine()) != null){
set.add(line.trim());
}
br.close();
setList.add(set);
}
return setList;
} catch (FileNotFoundException e) {
//Just return the empty setlist
return setList;
} catch (IOException e) {
//return a new empty list
return new ArrayList<Set<String>>();
}
}
But what I want is to allow the user of the method to specify the type of Set to instantiate (as long as it contains Strings of course). That is what the 'whatType' param is for.
All my research has lead me to how to instantiate an object given the class name, but that is not really what I am after here.
If you can use Java8, you can solve this problem easily. Declare the method as follows:
private static List<Set<String>> loadFiles(File[] files, Supplier<Set> setSupplier, Charset charSet)
Change your problem line to:
Set<String> set = setSupplier.get();
Then, in each call to this method, the setSupplier param can be easily provided using method references: HashSet::new, TreeSet::new...
How about using Class.newInstance() method? I coded a simple example for you:
public <T extends Set> void myMethod(Class<T> type) {
T object;
try {
object = type.newInstance();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
public void caller() {
myMethod(HashSet.class);
}
Is this what you are looking for?
If you assume the class has a no-argument accessible constructor, you're basically a newInstance() call away:
Set<String> set = (Set<String) whatType.newInstance();
Note that if you define whatType as a Class<? extends Set> instead of just a raw Class, you can get rid of this ugly cast too.
Overview; i need to create a json from a List to store in a sqlLite database. When i try to create the json Eclipse gets me an error that the variable List must be static. If this variable changed to static my application shows incorrect results and it's not a good thing. This is the class in which i create the json
public class Soluzione {
public String durata;
public List<Corsa> corse;
public Soluzione() {
corse = new ArrayList<Corsa>();
}
#Override
public String toString() {
StringBuilder str = new StringBuilder();
for (Corsa corsa : corse) {
if (str.length() > 0)
str.append('\n');
str.append(corsa.toString());
}
return str.toString();
}
public static JSONObject CreateJSon(List<Corsa> corse)
{
JSONObject jObj = new JSONObject();
try
{
Corsa prima = Soluzione.corse.get(0);
Corsa ultima = Soluzione.corse.get(corse.size()-1);
jObj.put("oraPartenza", prima.oraPartenza);
jObj.put("oraArrivo", ultima.oraArrivo);
jObj.put("partenza", prima.partenza);
jObj.put("arrivo", ultima.arrivo);
} catch (Exception e) { e.printStackTrace(); }
return jObj;
}
}
It is ambiguous between your field corse and the parameter of your method Create JSON.
Do not make method static and remove parameter
public JSONObject CreateJSon()
{
JSONObject jObj = new JSONObject();
try
{
Corsa prima = Soluzione.corse.get(0);
Corsa ultima = Soluzione.corse.get(corse.size()-1);
jObj.put("oraPartenza", prima.oraPartenza);
jObj.put("oraArrivo", ultima.oraArrivo);
jObj.put("partenza", prima.partenza);
jObj.put("arrivo", ultima.arrivo);
} catch (Exception e) { e.printStackTrace(); }
return jObj;
}
EDIT :
so if you want to keep CreateJSon static, rename the parameter name to avoid ambiguity then :
Soluzione soluzione = new Soluzione();
Soluzione.CreateJSon (soluzione.corse);
OR you want to remove static attribute and you can remove parameter and you do :
Soluzione soluzione = new Soluzione();
soluzione.CreateJSon ();
Ok so i have two classes: Content and TrackUserChanges . They have the same fields.
public class Content{
private Long id;
......
private SortedSet<Content> children = new TreeSet<Content>();
}
public class TrackUserChanges{
private Long id;
.....
private SortedSet<Content> children = new TreeSet<Content>();
}
I want to clone the data from Content to TrackUserChanges:
I have the children from an instance of content:
SortedSet<Content> children = content.getChildren();
This can contain many other contents, and that contents can have also children, etc.
SortedSet<TrackUserChanges> children1 = convertContentSetToTrackUserChangesSet(children);
This is the method:
public SortedSet<TrackUserChanges> convertContentSetToTrackUserChangesSet(SortedSet<Content> children){
SortedSet<TrackUserChanges> children1 = new TreeSet<TrackUserChanges>();
for(Content c : children){
TrackUserChanges trackU = new TrackUserChanges();
trackU.setCategory(c.getCategory());
trackU.setId(c.getId());
trackU.setBook(c.getBook());
trackU.setInsertUser(c.getInsertUser());
trackU.setParent(c.getParent());
trackU.setParentId(c.getParentId());
trackU.setRelativeSortOrder(c.getRelativeSortOrder());
trackU.setText(c.getText());
trackU.setType(c.getType());
children1.add(trackU);
}
return children1;
}
I need somehow to call recusively or something like that... and I can't do trackU.setChildren(c.getChildren()) because the types don't match :/
#Mifmif
try {
FileOutputStream fout = new FileOutputStream("a.dat");
ObjectOutputStream oos = new ObjectOutputStream(fout);
oos.writeObject(content);
oos.close();
}
catch (Exception e) { e.printStackTrace(); }
TrackUserChanges trackUserChanges11 = new TrackUserChanges();
try {
FileInputStream fin = new FileInputStream("a.dat");
MyCustomObjectInputStream custom = new MyCustomObjectInputStream(fin);
// custom.readClassDescriptor();
trackUserChanges11 = (TrackUserChanges) custom.readObject();
System.out.println("IDDDDD" + trackUserChanges11.getId());
custom.close();
}
catch (Exception e) { e.printStackTrace(); }
ClassCastException :)
If you have two classes with identical properties that have identical behaviour, separate those fields/behaviour into a separate class and extend that class in your other classes. This should allow you to copy directly between them.
Make your class implements Cloneable. Then just call the function clone of the SortedSet.
http://docs.oracle.com/javase/7/docs/api/java/lang/Cloneable.html
Here is a solution based on serialization , make both of your class serializable and if you want to go from one class instance to another, serialize your instance into a file , and read it using MyCustomObjectInputStream :
class MyCustomObjectInputStream extends ObjectInputStream {
public MyCustomObjectInputStream(InputStream in) throws IOException {
super(in);
}
#Override
protected ObjectStreamClass readClassDescriptor() throws IOException, ClassNotFoundException {
ObjectStreamClass resultClassDescriptor = super.readClassDescriptor();
if (resultClassDescriptor.getName().equals("name.of.the.package.OldClassName"))
resultClassDescriptor = ObjectStreamClass.lookup(name.of.the.package.NewClassName.class);
return resultClassDescriptor;
}
}
I resolved the problem
public TrackUserChanges convertContentToTrack(Content c) {
TrackUserChanges t = new TrackUserChanges();
t.setCategory(c.getCategory());
t.setId(c.getId());
t.setBook(c.getBook());
t.setInsertUser(c.getInsertUser());
t.setParent(c.getParent());
t.setParentId(c.getParentId());
t.setRelativeSortOrder(c.getRelativeSortOrder());
t.setText(c.getText());
t.setType(c.getType());
if (c.getChildren().size() == 0) {
return t;
}
SortedSet<TrackUserChanges> childs = new TreeSet<TrackUserChanges>();
for (Content content : c.getChildren()) {
childs.add(convertContentToTrack(content));
}
t.setChildren(childs);
return t;
}
Thanks anyway :)