Interface java Example Interview

 //interface Only public, static and final are allowed.

//No. Interfaces can’t have constructors.
interface Test{

    static  int s=2;
    final int d=4;
    void get();
    int getmultiple();

}


// initializers not allowed in interfaces
/*interface demoStatic(){
    {  System.out.println("empty implemented");}
    
    static{
         System.out.println("static implemented"); 
    }
}*/


interface B{
    int getdivide(int i);
    //  int getadd();//implementation is required in Class A
}

class A implements B{

    public int getdivide(int i ){
        return  i*i;
    }
}


class p{

    interface Q{
        int i=111;
    }
}

interface NextTest extends Test{
    int t=5;
    void get();

    int getadd();

    //  int getValue();//Demo is not abstract and does not override abstract method getValue() in NextTest
}

class Demo implements Test, NextTest {

    public int getadd(){
        return d+t;
    }

    public int getmultiple(){
        return d*t;
    }
    public void get(){
        System.out.println("demo get method implemented");
    }


}
class XDemo extends Demo{

}

/*class XXDemo implements NextTest{
    void methodD(){
        i=4;
        //No, because interface fields are static and 
        //final by default and you can’t change
        //their value once they are initialized. In the above code, methodB() 
        //is changing value of interface field A.i. It shows compile time error.
    }
}*/


public class MyClass {
    public static void main(String args[]) {

        System.out.println("Interface");

        Test s=new XDemo();
        s.get();
        //  System.out.println("sum : "+ s.getadd());//it will check in Test interface error not found

        System.out.println("multiple : "+ s.getmultiple());
        NextTest st=new XDemo();
        System.out.println("add : "+ st.getadd());

        // XDemo s=new NextTest();//NextTest is abstract; cannot be instantiated
        XDemo sp=new XDemo();
        System.out.println("addd : "+ sp.getadd());
        System.out.println("multiple : "+ sp.getmultiple());



        B newS=new A();

        System.out.println("divide : "+ newS.getdivide(12));
        // p ps=new Q();
        B bs=new B(){
            public int getdivide(int i){
                return i*i;          }

        };

        System.out.println("divide : "+  bs.getdivide(12));
    }
}

Find the character element which appears maximum number of times in an String

 //Find the element which appears maximum number of times in an array

import java.util.Arrays;
public class MyClass {
    public static void main(String args[]) {

        String name="amitrawat";

        char[] word=name.toCharArray();

        for(int i=0;i<word.length;i++){

            for(int j=i+1;j<word.length;j++){
                char first=word[i];
                char second=word[j];
                char temp;

                if(first>second){
                    temp=first;
                    word[i]=second;
                    word[j]=temp;
                }
            }

        }

        System.out.println("max number : " +  String.valueOf(word));


        //getting max character and times
        char maxchar=word[0];
        int times=0;
        for(int i=0;i<word.length;i++){

            char w=word[i];

            if(maxchar==w){
                times++;

            }else if(maxchar<w){
                times=1;
                maxchar=w;

            }
        }

        System.out.println("char max  : " + maxchar);
        System.out.println("char times: " + times);
    }
}

OUTPUT

max number : aaaimrttw
char max  : w
char times: 1

Find the element which appears maximum number of times in an array

import java.util.Arrays;
public class MyClass {
    public static void main(String args[]) {
        int max = 0, count = 0;
        int[] a={1,2,3,4,8,8,9,8,3,3,5,3,4,5,6,8};

        //sorting array   
        for(int i=0;i<a.length;i++){

            for(int j=i+1;j<a.length;j++){
                int first=a[i];
                int second=a[j];
                int temp=0;

                if(first>second){

                    temp=first;
                    a[i]=second;
                    a[j]=temp;

                }
            }
        }
        //  Arrays.sort(a);
        //finding highest number with times
        for(int i=0;i<a.length;i++){
            int num=a[i];

            if(max==num){
                count++;
            }else if(max<num){
                max=num;
                count=1;

            }
        }

        System.out.println("max number : " + max);
        System.out.println("times: " + count);
        
    }
}

OUTPUT

max number : 9
times: 1

Overloading and overriding Interview Example Code

 class Test {

    static int s = 4;
    final int d = 5;

    static void sit() {
        System.out.println(" sit method of  test class ");
    }

    void get() {
        System.out.println("  get method test class");

    }
}

class Test1 extends Test {
    static int s = 6;
    static int a = 2;
    final int d = 3;

    static void sit() {
        System.out.println("sit  method test1 class");
    }

    void get() {

        System.out.println("get  method get test1 class");
    }
}

class Test2 extends Test1 {
    static int s = 7;

    static void sit() {
        System.out.println("sit method test2 class");
    }

    void get() {
        System.out.println("get  method get test2 class");
    }

}

class Demo {
}

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("1 : test2 class instance of test2 class.......... ");
        System.out.println();
        Test2 obj2 = new Test2();
        //class c inherit static 
        System.out.println("static varialble : " + obj2.a); // 2
        System.out.println();

        System.out.println("final varibale : " + obj2.d); //3
        System.out.println();

        obj2.sit();//print method of test2 class 

        System.out.println();
        System.out.println();

        System.out.println("2 : test1 class instance of test2 class.......... ");
        System.out.println();
        Test1 obj1 = new Test2();

        obj1.sit();// print method of class test1 : static method
        System.out.println();


        obj1.get();//print method of class test2 :non static method
        System.out.println();


        //testing the type cast 
        Test objtrail1 = new Test1();//correct
        Test objtrail2 = new Test2();//correct

        // Test1 cannot be converted to Test2
        //     Test2 objtrail3=new Test1();//incorrect type cast error 

        // incompatible types: Test cannot be converted to Test2
        //    Test2 objtrail3=new Test();//incorrect type cast error


        //    Test1 obje=new Test();//error: incompatible types: Test cannot be converted to Test1

        System.out.println();
        System.out.println();
        System.out.println("3 : test class instance of test1 class.......... ");

        Test obje = new Test1();//the instance of test1 but print the static and final variable and static method of test
        System.out.println();

        System.out.println("print the static  variable of test class  " + obje.s);//4
        System.out.println();

        System.out.println("print the final  variable of test  class " + obje.d);//5
        System.out.println();

        obje.sit();//print the method of static test class 
        System.out.println();

        obje.get();//print method of non static test1 class

        System.out.println();


        //    System.out.println("3 : test2 class instance of test class.......... "); 


        // Test2 objet=new Test();

        // objet.sit();//error: incompatible types: Test cannot be converted to Test2
        //    Test2 objet=new Test1();//error: incompatible types: Test1 cannot be converted to Test2


        //    Test s=new Demo();//error: incompatible types: Demo cannot be converted to Test
    }
}

output :  

1 : test2 class instance of test2 class.......... 

static varialble : 2

final varibale : 3

sit method test2 class


2 : test1 class instance of test2 class.......... 

sit  method test1 class

get  method get test2 class



3 : test class instance of test1 class.......... 

print the static  variable of test class  4

print the final  variable of test  class 5

 sit method of  test class 

get  method get test1 class

LocaleHelper for language change

 import android.content.Context;

import android.content.SharedPreferences;
import android.content.res.Configuration;
import android.content.res.Resources;
import android.os.Build;
import android.os.LocaleList;
import android.preference.PreferenceManager;

import java.util.Locale;

public class LocaleHelper {

    private static final String SELECTED_LANGUAGE = "Locale.Helper.Selected.Language";

    public static String getLanguage(Context context) {
        return getPersistedData(context, Locale.getDefault().getLanguage());
    }

    public static Context setNewLocale(Context mContext, String language) {
        persist(mContext, language);
        return updateLocale(mContext, getLanguage(mContext));
    }

    public static Context setLocale(Context context) {
        persist(context, getLanguage(context));

        return updateLocale(context, getLanguage(context));
    }

    private static String getPersistedData(Context context, String defaultLanguage) {
        SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(context);
        return preferences.getString(SELECTED_LANGUAGE, defaultLanguage);
    }

    private static void persist(Context context, String language) {
        SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(context);
        SharedPreferences.Editor editor = preferences.edit();

        editor.putString(SELECTED_LANGUAGE, language);
        editor.apply();
    }
    

    private static Context updateLocale(Context context, String lang) {
        Resources resources = context.getResources();
        Configuration configuration = resources.getConfiguration();

        Locale localeToSwitchTo = new Locale(lang);

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {

            configuration.setLocale(localeToSwitchTo);

            LocaleList localeList = new LocaleList(localeToSwitchTo);
            LocaleList.setDefault(localeList);
            configuration.setLocales(localeList);
            context = context.createConfigurationContext(configuration);

        } else {

            Locale.setDefault(localeToSwitchTo);
            configuration.locale = localeToSwitchTo;
            resources.updateConfiguration(configuration, resources.getDisplayMetrics());
        }

        return context;
    }
}

//Activity class 

@Override
protected void attachBaseContext(Context base) {
    super.attachBaseContext(LocaleHelper.setLocale(base));
}

private void setNewLocale(Context mContext, String language) {
    try {
        LocaleHelper.setNewLocale(this, language);
         recreate();
        //recreate activity
    } catch (Exception e) {
        e.printStackTrace();
        FirebaseCrashlytics.getInstance().recordException(e);
    }

}

In Android EditText, how to force writing uppercase?

In Android EditText, how to force writing uppercase? 

@Override

public void setFilters(InputFilter[] filters) {
    try {
        InputFilter[] oldFilter = filters;
        InputFilter[] newFilters = new InputFilter[oldFilter.length + 1];
        System.arraycopy(oldFilter, 0, newFilters, 0, oldFilter.length);
        newFilters[newFilters.length - 1] = new InputFilter.AllCaps();
        super.setFilters(newFilters);
    } catch (Exception e) {
        e.printStackTrace();
        FirebaseCrashlytics.getInstance().recordException(e);
    }

}

Disabling Android O auto-fill service for an application

So I have my own class which is extends the android.support.v7.widget.AppCompatEditText

 and all I did is overwrote the following method with the following value:

@Override
public int getAutofillType() {
    return AUTOFILL_TYPE_NONE;
}

no other solutions worked, not even android:importantForAutofill="no".

getAutofillType() comes from the View class, so it should work for every other 

class such as TextInputEditText too!

Firebase : -Firestore Live Location

FIRESTORE Live Location 

AUTHENTICATION:-

EDIT RULES :-

rules_version = '2';
service cloud.firestore {
    match /databases/{database}/documents {
        match /dev/{userId} {
            allow read, update, delete: if request.auth.uid == userId;
            allow create: if request.auth.uid != null;
            match /LiveData/{userId} {
                allow read, update, delete,create: if request.auth.uid != null;

            }
        }
    }

}

ANDROID CODE:

String token;

FirebaseAuth authref;
private FirebaseFirestore db;
<string name="FIREBASE_DATABASE_NAME">dev</string>
<string name="FIREBASE_DATABASE_NODE_NAME">LiveData</string>
<string name="FIREBASE_EMAIL_DB">amitrawat@gmail.com</string>
<string name="FIREBASE_PASS_DB">123456789</string>
@Override
public void onCreate() {
    super.onCreate();
  
    try {
        setup();
        notificationToken();
        loginFirebase();
    } catch (Exception e) {
        e.printStackTrace();
  
    }


}
public void setup() {
   
    db = FirebaseFirestore.getInstance();
   
}

private void notificationToken() throws Exception {
    try {
        FirebaseInstanceId.getInstance().getInstanceId()
                .addOnCompleteListener(new OnCompleteListener<InstanceIdResult>() {
                    @Override
                    public void onComplete(@NonNull Task<InstanceIdResult> task) {
                        if (!task.isSuccessful()) {
                            return;
                        }
                        token = task.getResult().getToken();

                        Log.e("token", token);
                    }
                });
    } catch (Exception e) {
        throw new Exception(e);
    }
}

  private void loginToFirebase() {
//Authenticate with Firebase, using the email and password we created earlier//
        String email = getString(R.string.FIREBASE_EMAIL_DB);
        String password = getString(R.string.FIREBASE_PASS_DB);
//Call OnCompleteListener if the user is signed in successfully//
        authref = FirebaseAuth.getInstance();
        authref.signInWithEmailAndPassword(
                email, password).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(Task<AuthResult> task) {
                if (task.isSuccessful()) {
                    try {
                        requestLocationUpdates();
                    } catch (Exception e) {
                      
                    }

                } else {
                    Log.d(TAG, "Firebase authentication failed");
                }
            }
        });
    }


 private void requestLocationUpdates() {
    
        LocationRequest request = new LocationRequest();
        request.setInterval(60000);
        request.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
        FusedLocationProviderClient client = LocationServices.getFusedLocationProviderClient(this);
        int permission = ContextCompat.checkSelfPermission(this,
                Manifest.permission.ACCESS_FINE_LOCATION);
//If the app currently has access to the location permission...//
        if (permission == PackageManager.PERMISSION_GRANTED) {
//...then request location updates//
            client.requestLocationUpdates(request, new LocationCallback() {
                @Override
                public void onLocationResult(LocationResult locationResult) {
//Get a reference to the database, so your app can perform read and write operations//
                    if (isNullOrEmpty(token)) {
                        try {
                            notificationToken();
                        } catch (Exception e) {
                            e.printStackTrace();
                            Util.Crash(e);
                        }
                    } else {
                        try {
                          
                            Location location = locationResult.getLastLocation();
                            if (location != null) {
                                FirebaseDTO locdto = new FirebaseDTO ();
                                locdto.setLatitude(location.getLatitude());
                                locdto.setLongitude(location.getLongitude());
                              
                                locdto.setLastUpdatedOn(String.valueOf(new Timestamp(System.currentTimeMillis())));
                                Log.e("loc1", String.valueOf(location.getLatitude()));
                                Log.e("loc2", String.valueOf(location.getLongitude()));
                               

                                // Add a new document with a generated ID\

                                db.collection(getResources().getString(R.string.FIREBASE_DATABASE_NAME)).
                                        document(authref.getUid()).
                                        collection(getResources().getString(R.string.FIREBASE_DATABASE_NODE_NAME)).
                                        document(token).
                                        set(locdto)
                                        .addOnSuccessListener(new OnSuccessListener<Void>() {
                                            @Override
                                            public void onSuccess(Void aVoid) {
                                                Log.d(TAG, "DocumentSnapshot successfully written!");
                                            }
                                        })
                                        .addOnFailureListener(new OnFailureListener() {
                                            @Override
                                            public void onFailure(@NonNull Exception e) {
                                                Log.w(TAG, "Error writing document", e);
                                            }
                                        });

                            }


                        } catch (Exception e) {
                            Util.Crash(e);
                        }

                    }

                }
            }, null);
        }
    }
public class FirebaseDTO {
    private double latitude;
    private double longitude
    private String lastUpdatedOn;

}

 

Alert Dialog in flutter

 Alert Dialog in flutter

 new IconButton(
  icon: new Icon(Icons.cloud_download_rounded),
  highlightColor: Colors.orange,
  iconSize: 30,
  onPressed: () {
    showDialog(
        context: context,
        builder: (BuildContext context) {
          return getDialogBox();
        });
  },
),

method of AlertDialog 

AlertDialog getDialogBox() {
  return AlertDialog(
    title: Row(children: [
      new IconButton(
        icon: new Icon(Icons.warning_amber_outlined),
        color: Colors.black45,
        highlightColor: Colors.orange,
        iconSize: 30,
        onPressed: () {
          showDialog(
              context: context,
              builder: (BuildContext context) {
                return getDialogBox();
              });
        },
      ),
      /* Image.network(
        'https://flutter-examples.com/wp-content/uploads/2019/12/android_icon.png',
        width: 50,
        height: 50,
        fit: BoxFit.contain,
      ),*/
      Text(' Download ')
    ]),
    content: Text("Are You Sure Want To Proceed?"),
    actions: <Widget>[
      TextButton(
        child: Text("YES"),
        onPressed: () {
          //Put your code here which you want to execute on Yes button click.
          Navigator.of(context).pop();
        },
      ),
      TextButton(
        child:
        Text("CANCEL"),
        onPressed: () {
          //Put your code here which you want to execute on Cancel button click.
          Navigator.of(context).pop();
        },
      ),
    ],
  );
}

A non-null String must be provided to a Text widget in Flutter

A non-null String must be provided to a Text widget in Flutter

you can check null safe .

new Text(cart_prod_qty!=null?cart_prod_qty:'Default Value'),

How to change Package name in Flutter?

FOR ANDROID APP NAME

change the label name in your AndroidManifes.xml

<application android:name="io.flutter.app.FlutterApplication" android:label="TheNameOfYourApp"

FOR PACKAGE NAME

Change the package name in your AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="your.package.name">

Also in your build.gradle file inside app folder

defaultConfig { applicationId "your.package.name" minSdkVersion 16 targetSdkVersion 28 resConfigs "en" versionCode flutterVersionCode.toInteger() versionName flutterVersionName testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner" }

finally change the package in your MainActivity.java 

class(if the MainActivity.java is not 

avaiable ,check the MainActivity.kt

package your.package.name; import android.content.ComponentName; import android.content.Intent; import android.net.Uri; import android.util.Log; import androidx.annotation.NonNull; public class MainActivity extends FlutterActivity {}

Change the directory name:

From

android\app\src\main\java\com\example\name

To.

android\app\src\main\java\your\package\name

IOS

in ios the package name is the bundle identifier in Info.plist

<key>CFBundleIdentifier</key> <string>$(PRODUCT_BUNDLE_IDENTIFIER)</string>

which is found in Runner.xcodeproj/project.pbxproj

PRODUCT_BUNDLE_IDENTIFIER = com.example.appname;

Flutter custom listview with cardview and icon android studio

                      

                  Flutter custom listview with cardview and icon android studio

1.Add dependencies fluttertoast: ^4.0.1 in pubspec.yaml

dependencies: flutter: sdk: flutter cupertino_icons: ^0.1.3 fluttertoast: ^4.0.1

 

2.Create lib/main.dart 

import 'package:flutter/material.dart'; import 'package:listviewdemo/listview_activity.dart'; void main() { runApp(MyApp()); } class MyApp extends StatelessWidget { // This widget is the root of your application. @override Widget build(BuildContext context) { return MaterialApp( title: 'Flutter Demo', theme: ThemeData( primarySwatch: Colors.purple, visualDensity: VisualDensity.adaptivePlatformDensity, ), home: ListViewActivity(title: 'EmailPageList'), ); } }

 

3.Create lib/email_data.dart model 

class EmailData { EmailData({this.name, this.email, this.phonenumber}); final String name; final String email; final String phonenumber; } List<EmailData> allEmail = [ EmailData( name: 'Amit Rawat', email: 'amit.rawat@me.com', phonenumber: '+109938388380'), EmailData( name: 'John Ricciardi', email: 'John.ricciardi@me.com', phonenumber: '+109938388380'), EmailData( name: 'David Smith ', email: 'David.Smith@me.com', phonenumber: '+109938388380'), EmailData( name: 'Michael Hassinger', email: 'Michael.hassinger@me.com', phonenumber: '+109938388380'), EmailData( name: 'Chris Cupps', email: 'Chris.cupps@me.com', phonenumber: '+1099383-08380'), EmailData( name: 'Mike Nantz', email: 'Mike.nantz@me.com', phonenumber: '+10993838-8380'), EmailData( name: 'Mark Primus', email: 'Mark.primus@me.com', phonenumber: '+1099383-88380'), EmailData( name: 'Muriel Lewellyn', email: 'muriel.lewellyn@me.com', phonenumber: '+1099-38388380'), EmailData( name: 'Hunter Giraud', email: 'Hunter.giraud@me.com', phonenumber: '+109938388-380'), EmailData( name: 'Corina Whiddon', email: 'corina.whiddon@me.com', phonenumber: '+10993838-8380'), EmailData( name: 'Meaghan Covarrubias', email: 'meaghan.covarrubias@me.com', phonenumber: '+10993838-8380'), EmailData( name: 'Daniel Severson', email: 'Daniel .severson@me.com', phonenumber: '+109938388-380'), EmailData( name: 'Maria Baxter', email: 'Maria .baxter@me.com', phonenumber: '+109938388-380'), EmailData( name: 'Alessandra Kahn', email: 'alessandra.kahn@me.com', phonenumber: '+109938388-380'), EmailData( name: 'James Saari', email: 'James .saari@me.com', phonenumber: '+109938388-380'), EmailData( name: 'Valeria Salvador', email: 'valeria.salvador@me.com', phonenumber: '+109938388-380'), EmailData( name: 'Fredrick Folkerts', email: 'fredrick.folkerts@me.com', phonenumber: '+109938388-380'), EmailData( name: 'Delmy Izzi', email: 'delmy.izzi@me.com', phonenumber: '+09938388-380'), EmailData( name: 'Leann Klock', email: 'leann.klock@me.com', phonenumber: '+09938388-380'), EmailData( name: 'Rhiannon Macfarlane', email: 'rhiannon.macfarlane@me.com', phonenumber: '+09938388-380'), ];

4.Create lib/listview_activity.dart

import 'package:flutter/cupertino.dart'; import 'package:flutter/material.dart'; import 'package:listviewdemo/email_data.dart'; import 'listview_title.dart'; class ListViewActivity extends StatelessWidget { ListViewActivity({Key key, this.title}) : super(key: key); final String title; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text(this.title), ), body: Container( child: _buildList(), ), ); } Widget _buildList() { return ListView.builder( itemCount: allEmail.length, itemBuilder: (BuildContext context, int index) { EmailData data = allEmail[index]; return Card( elevation: 8.0, child: Container( child: EmailListTile(data), ), ); }); } }

5.Create lib/listview_title.dart

import 'package:flutter/material.dart'; import 'package:fluttertoast/fluttertoast.dart'; import 'package:listviewdemo/email_data.dart'; class EmailListTile extends ListTile { EmailListTile(EmailData data) : super( title: Text(data.name), subtitle: Column( crossAxisAlignment: CrossAxisAlignment.start, children: <Widget>[ new Text(data.email), new Text(data.phonenumber) ], ), leading: CircleAvatar(child: Text(data.name[0])), dense: false, trailing: Icon( Icons.arrow_forward, size: 24.0, color: Colors.deepPurple, ), onTap: () { Fluttertoast.showToast( msg: data.email, toastLength: Toast.LENGTH_SHORT, gravity: ToastGravity.CENTER, timeInSecForIosWeb: 1, backgroundColor: Colors.grey, textColor: Colors.white, fontSize: 14.0); }); }