How to store data using Firebase in android?

Step 0: First create a class in which you set and get values of object you want to store on firebase

public class User {

    public String mUsername;

    public User(){
        // Default constructor required for calls to DataSnapshot.getValue(User.class)
    }

    public User( String userName){
        this.mUsername = userName;
    }
}

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Step 1: Now we create layout to get user name as input

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <EditText
        android:id="@+id/etUsername"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
    <Button
        android:id="@+id/btnSave"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Save"/>

</LinearLayout>

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Step 2: Now we store value that we take from user on firebase

import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.design.widget.TextInputLayout;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;

public class UserWelcome extends AppCompatActivity {

    private FirebaseAuth mAuth;
    private FirebaseAuth.AuthStateListener mAuthListener;
    private DatabaseReference mDatabaseReference;
    private FirebaseDatabase mFirebaseDatabase;

    private String TAG = "UserWelcome";
    private EditText mUsername;
    private Button mBtnGetstarted;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_user_welcome);


        mAuth = FirebaseAuth.getInstance();
        mFirebaseDatabase = FirebaseDatabase.getInstance();
        mDatabaseReference = mFirebaseDatabase.getReference();

        mUsername = findViewById(R.id.etUsername);
        mBtnGetstarted = findViewById(R.id.btnSave);

       mAuthListener = new FirebaseAuth.AuthStateListener() {
           @Override
           public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
               FirebaseUser user = firebaseAuth.getCurrentUser();

               if (user != null) {
                   // User is signed in
                   Log.d(TAG, "onAuthStateChanged:signed_in:" + user.getUid());
                   toastMessage("Successfully signed in with: " + user.getEmail());
               } else {
                   // User is signed out
                   Log.d(TAG, "onAuthStateChanged:signed_out");
                   toastMessage("Successfully signed out.");
               }

           }
       };

        // Read from the database
        mDatabaseReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                // This method is called once with the initial value and again
                // whenever data at this location is updated.
                Object value = dataSnapshot.getValue();
                Log.d("user name", "Value is: " + value);
            }

            @Override
            public void onCancelled(DatabaseError error) {
                // Failed to read value
                Log.w("user name", "Failed to read value.", error.toException());
            }
        });

        mBtnGetstarted.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try{
                    if(mUsername. getText().toString().isEmpty()){
                        mUsername.setError("please enter name");
                        mUsername.setErrorEnabled(true);
                    }else{
                            FirebaseUser user = mAuth.getCurrentUser();
                            String userID = user.getUid();
                            mDatabaseReference.child(userID).child("UserName").setValue(mUsername. getText().toString().trim());
                            toastMessage("Adding " + mUsername. getText().toString().trim() + " to database...");
                        Intent mainIntent = new Intent( UserWelcome.this , MainActivity.class);
                        startActivity(mainIntent);
                    }


                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        });



    }

    @Override
    public void onStart() {
        super.onStart();
        mAuth.addAuthStateListener(mAuthListener);
    }

    @Override
    public void onStop() {
        super.onStop();
        if (mAuthListener != null) {
            mAuth.removeAuthStateListener(mAuthListener);
        }
    }

    public void toastMessage( String msg){
        Toast.makeText(getApplicationContext() ,msg , Toast.LENGTH_SHORT).show();
    }
}

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In this tutorial we will learn about how to store data on firebase realtime database

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#java #howto #interviewquestions #mobile

How to use Java Swing to create a button

import javax.swing.*;  
public class FirstSwingExample {  
public static void main(String[] args) {  
JFrame f=new JFrame();//creating instance of JFrame  
          
JButton b=new JButton("click");//creating instance of JButton  
b.setBounds(130,100,100, 40);//x axis, y axis, width, height  
          
f.add(b);//adding button in JFrame  
          
f.setSize(400,500);//400 width and 500 height  
f.setLayout(null);//using no layout managers  
f.setVisible(true);//making the frame visible  
}  
}

#java #gfg #geeksforgeeks #lecture #recursion #rope cutting

Rope Cutting Problem

import java.io.*;
import java.util.*;

class GFG 
{
	static int maxCuts(int n, int a, int b, int c)
	{
		if(n == 0) return 0;
		if(n < 0)  return -1;

		int res = Math.max(maxCuts(n-a, a, b, c), 
		          Math.max(maxCuts(n-b, a, b, c), 
		          maxCuts(n-c, a, b, c)));

		if(res == -1)
			return -1;

		return res + 1; 
	}
  
    public static void main(String [] args) 
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    	int n = 5, a = 2, b = 1, c = 5;
    	
    	System.out.println(maxCuts(n, a, b, c));
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}

#java #interviewquestions #search

How to binary search in Java

import java.util.Stack;

/**
 * Java Program to implement a binary search tree. A binary search tree is a
 * sorted binary tree, where value of a node is greater than or equal to its
 * left the child and less than or equal to its right child.
 * 
 * @author WINDOWS 8
 *
 */
public class BST {

    private static class Node {
        private int data;
        private Node left, right;

        public Node(int value) {
            data = value;
            left = right = null;
        }
    }

    private Node root;

    public BST() {
        root = null;
    }

    public Node getRoot() {
        return root;
    }

    /**
     * Java function to check if binary tree is empty or not
     * Time Complexity of this solution is constant O(1) for
     * best, average and worst case. 
     * 
     * @return true if binary search tree is empty
     */
    public boolean isEmpty() {
        return null == root;
    }

    
    /**
     * Java function to return number of nodes in this binary search tree.
     * Time complexity of this method is O(n)
     * @return size of this binary search tree
     */
    public int size() {
        Node current = root;
        int size = 0;
        Stack<Node> stack = new Stack<Node>();
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            if (current != null) {
                stack.push(current);
                current = current.left;
            } else {
                size++;
                current = stack.pop();
                current = current.right;
            }
        }
        return size;
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    /**
     * Java function to clear the binary search tree.
     * Time complexity of this method is O(1)
     */
    public void clear() {
        root = null;
    }

}

#android #dart #flutter #ios #helloworld

All the code you need to run Hello World in Flutter using a Stateless widget

import 'package:flutter/material.dart';

void main() {
  runApp(
    new MaterialApp(
      title: 'Hello World App',
      home: new myApp(),
    )
  );
}

class myApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Hello World App'),
      ),
      body: new Center(
        child: new Text(
          'Hello, world!'
        ),
      ),
    );
  }
}

#java #java #arraylists #while-loops #equala

How to insert ArrayList into While-condition?

List<String> songList = new ArrayList<>();
songList.add("Some song"); //Repeat until satisfied

System.out.println("\n\tWelcome! Please choose a song!");
String songChoice = scan.nextLine();
while (!songList.contains(songChoice)) {
    //Do stuff when input is not a recognised song
}

#java #gfg #geeksforgeeks #arrays #practice #frequencycount #frequencies #limitedrange

Frequencies of Limited Range Array Elements

class Solution{
    //Function to count the frequency of all elements from 1 to N in the array.
    public static void frequencyCount(int arr[], int N, int P)
    {
        //Decreasing all elements by 1 so that the elements
        //become in range from 0 to n-1.
        int maxi = Math.max(P,N);
        int count[] = new int[maxi+1];
        Arrays.fill(count, 0);
        for(int i=0;i<N;i++){
            count[arr[i]]++; 
        }
        
        for(int i=0;i<N;i++){
            arr[i] = count[i+1];
        }
    }
}

#android

Authenticating Your Client | Google APIs for Android

keytool -exportcert -list -v \
-alias <your-key-name> -keystore <path-to-production-keystore>

#java

How to efficiently iterate over each entry in a Java Map

Map<String, String> map = ...
for (Map.Entry<String, String> entry : map.entrySet()) {
    System.out.println(entry.getKey() + "/" + entry.getValue());
}

#java

Print Nested Array in Java

String[][] deepArray = new String[][] {{"John", "Mary"}, {"Alice", "Bob"}};
System.out.println(Arrays.toString(deepArray));
//output: [[Ljava.lang.String;@106d69c, [Ljava.lang.String;@52e922]
System.out.println(Arrays.deepToString(deepArray));

#java #java #2dchar array

How do you check a row in a 2D char array for a specific element and then count how many of that element are in the row? (Java)

private boolean oneQueenPerRow() {
    int foundQueens;
    for (int i = 0; i < board.length; i++) {
        foundQueens = 0;//each loop is a checked row
        for (int j = 0; j < board.length; j++) {
            if (board[i][j] == QUEEN)
                foundQueens++;
        }
        if (foundQueens > 1) return false;
    }
    return true;
}

#java #logic #algorithms #interesting #arrays

Flood Fill Algorithm: Like the bucket tool in Paint app but for multi-dimensional arrays

import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.Queue;

class Pair {
    int x, y;

    public Pair(int x, int y) {
        this.x = x;
        this.y = y;
    }
}

class FloodFill
{
    // Below arrays details all 8 possible movements
    private static final int[] row = { -1, -1, -1, 0, 0, 1, 1, 1 };
    private static final int[] col = { -1, 0, 1, -1, 1, -1, 0, 1 };

    // check if it is possible to go to pixel (x, y) from
    // current pixel. The function returns false if the pixel
    // has different color or it is not a valid pixel
    public static boolean isSafe(char[][] M, int m, int n,
                                int x, int y, char target)
    {
        return x >= 0 && x < m && y >= 0 && y < n
                && M[x][y] == target;
    }

    // Flood fill using BFS
    public static void floodfill(char[][] M, int x, int y, char replacement)
    {
        int m = M.length;
        int n = M[0].length;

        // create a queue and enqueue starting pixel
        Queue<Pair> q = new ArrayDeque<>();
        q.add(new Pair(x, y));

        // get target color
        char target = M[x][y];

        // run till queue is not empty
        while (!q.isEmpty())
        {
            // pop front node from queue and process it
            Pair node = q.poll();

            // (x, y) represents current pixel
            x = node.x;
            y = node.y;

            // replace current pixel color with that of replacement
            M[x][y] = replacement;

            // process all 8 adjacent pixels of current pixel and
            // enqueue each valid pixel
            for (int k = 0; k < row.length; k++)
            {
                // if adjacent pixel at position (x + row[k], y + col[k]) is
                // a valid pixel and have same color as that of current pixel
                if (isSafe(M, m, n, x + row[k], y + col[k], target))
                {
                    // enqueue adjacent pixel
                    q.add(new Pair(x + row[k], y + col[k]));
                }
            }
        }
    }

    public static void main(String[] args)
    {
        // matrix showing portion of the screen having different colors
        char[][] M = {
            "YYYGGGGGGG".toCharArray(),
            "YYYYYYGXXX".toCharArray(),
            "GGGGGGGXXX".toCharArray(),
            "WWWWWGGGGX".toCharArray(),
            "WRRRRRGXXX".toCharArray(),
            "WWWRRGGXXX".toCharArray(),
            "WBWRRRRRRX".toCharArray(),
            "WBBBBRRXXX".toCharArray(),
            "WBBXBBBBXX".toCharArray(),
            "WBBXXXXXXX".toCharArray()
        };

        // start node
        int x = 3, y = 9;   // target color = "X"

        // replacement color
        char replacement = 'C';

        // replace target color with replacement color
        floodfill(M, x, y, replacement);

        // print the colors after replacement
        for (int i = 0; i < M.length; i++) {
            System.out.println(Arrays.toString(M[i]));
        }
    }
}

#java

Finding all classes implementing a specific interface

public <T> List<Class<? extends T>> findAllMatchingTypes(Class<T> toFind) {
    foundClasses = new ArrayList<Class<?>>();
    List<Class<? extends T>> returnedClasses = new ArrayList<Class<? extends T>>();
    this.toFind = toFind;
    walkClassPath();
    for (Class<?> clazz : foundClasses) {
        returnedClasses.add((Class<? extends T>) clazz);
    }
    return returnedClasses;
}

#java #gfg #geeksforgeeks #lecture #sorting #bubblesort

Bubble Sort

// Optimised Bubble Sort

import java.io.*;

class GFG {
    
    static void bubbleSort(int arr[], int n){
        boolean swapped;
        
        for(int i = 0; i < n; i++){
            
            swapped = false;
            
            for(int j = 0; j < n - i - 1; j++){
                if( arr[j] > arr[j + 1]){
                    
                    // swapping
                    int temp = arr[j];
                    arr[j] = arr[j+1];
                    arr[j+1] = temp;
                    
                    swapped = true;
                    
                }
            }
            if(swapped == false)
            break;
        }
    }
    
	public static void main (String[] args) {
	    int a[] = {2, 1, 4, 3};
	    bubbleSort(a, 4);
	    
	    for(int i = 0; i < 4; i++){
	        System.out.print(a[i] + " ");     // OUTPUT : 1 2 3 4
	    }
	}
}






// Bubble Sort

import java.io.*;

class GFG {
    
    static void bubbleSort(int arr[], int n){
        for(int i = 0; i < n; i++){
            for(int j = 0; j < n - i - 1; j++){
                if( arr[j] > arr[j + 1]){
                    
                    // swapping
                    int temp = arr[j];
                    arr[j] = arr[j+1];
                    arr[j+1] = temp;
                    
                }
            }
        }
    }
    
	public static void main (String[] args) {
	    int a[] = {2, 1, 4, 3};
	    bubbleSort(a, 4);
	    
	    for(int i = 0; i < 4; i++){
	        System.out.print(a[i] + " ");     // OUTPUT : 1 2 3 4
	    }
	}
}

#java #gfg #geeksforgeeks #lecture #sorting #selectionsort

Selection Sort

import java.io.*;

class GFG {
    
    static void selectionSort(int arr[], int n){
        for(int i = 0; i < n; i++){
            int min_ind = i;
            
            for(int j = i + 1; j < n; j++){
                if(arr[j] < arr[min_ind]){
                    min_ind = j;
                }
            }
            
            int temp = arr[i];
            arr[i] = arr[min_ind];
            arr[min_ind] = temp;
        }
    }
    
	public static void main (String[] args) {
	    int a[] = {2, 1, 4, 3};
	    selectionSort(a, 4);
	    
	    for(int i = 0; i < 4; i++){
	        System.out.print(a[i] + " ");    // OUTPUT : 1 2 3 4
	    }
	}
}

#android #java

Intent to Start New Activity in Android Studio

// IntendedActivity - the file you wish to open
// CurrentActivity - the file where this code is placed  

Intent intent = new Intent (this, IntendedActivity.class);
    CurrentActivity.this.startActivity(intent);

How to store data using Firebase in android?

Step 0: First create a class in which you set and get values of object you want to store on firebase

Step 1: Now we create layout to get user name as input

Step 2: Now we store value that we take from user on firebase

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