Part 12 - Students Problem Solving

 Java Part : 

package first.learn.passingdatabetweenactivities;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    EditText etName;
    Button btnSimpleString;

    TextView textTwo,
    textOne;


    void  add (int a, int b){
        int c = a+b;
        textTwo.setText(""+c);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textTwo = (TextView)findViewById(R.id.textTwo);

       add (10, 20);






        etName = (EditText) findViewById(R.id.etName);

        btnSimpleString = (Button) findViewById(R.id.btnSimpleString);

       

    }
}

Xml Part : 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:orientation="vertical"
    android:layout_margin="16dp">



    <TextView
        android:hint="Text One... "
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/textOne"/>


    <TextView
        android:hint="Text two... "
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/textTwo"/>

   <EditText
       android:layout_marginTop="25dp"
       android:hint="write...."
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:id="@+id/etName"/>

    <Button
        android:id="@+id/btnSimpleString"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Simple String"/>

</LinearLayout>

Part 10 - Passing Data Between Activities - Method One

 Java Part One : 

package first.learn.passingdatabetweenactivities;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

    EditText etName;
    Button btnSimpleString;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        etName = (EditText) findViewById(R.id.etName);

        btnSimpleString = (Button) findViewById(R.id.btnSimpleString);

        btnSimpleString.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                String s = etName.getText().toString();

                if(TextUtils.isEmpty(s)){
                    etName.setError("Empty");
                    return;
                }

                etName.setError(null);


                Intent intent = new Intent(MainActivity.this, DataGettingActivity.class );

                intent.putExtra("StringPacket", s );

                startActivity(intent);

            }
        });

    }
}

xml part One : 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:orientation="vertical"
    android:layout_margin="16dp">

   <EditText
       android:hint="write...."
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:id="@+id/etName"/>

    <Button
        android:id="@+id/btnSimpleString"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Simple String"/>

</LinearLayout>

Java Part Two : 

package first.learn.passingdatabetweenactivities;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.TextView;

public class DataGettingActivity extends AppCompatActivity {

    TextView tvData;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_data_getting);

        setTitle("Data Getting Activity");

        tvData = (TextView) findViewById(R.id.tvData);


        if(getIntent()!=null){

            if(getIntent().getStringExtra("StringPacket")!=null){

                String gettingString = getIntent().getStringExtra("StringPacket");

                tvData.setText(gettingString);

            }
        }


    }
}

Xml Part Two : 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".DataGettingActivity"
    android:layout_margin="16dp">


    <TextView
        android:id="@+id/tvData"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="30dp"
        android:text="Text"
        android:gravity="center"
        android:layout_marginTop="25dp"/>


</LinearLayout>

Sample App - Calculator With JavaScript Library Rhino

Dependency : 

implementation 'com.faendir.rhino:rhino-android:1.5.2'

 Java Part : 

package first.learn.calculator;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

import com.google.android.material.button.MaterialButton;
import org.mozilla.javascript.Context;
import org.mozilla.javascript.Scriptable;


public class MainActivity extends AppCompatActivity implements View.OnClickListener {


    TextView tvMath, tvResult;
    MaterialButton btnDoubleZero, btnZero, btnDot, btnEqual, btnOne, btnTwo, btnThree, btnFour,
            btnFive, btnSix, btnSeven, btnEight, btnNine, btnPlus, btnMinus, btnMultiply, btnDivide,
            btnBracketOpen, btnBracketEnd, btnC;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        tvMath = (TextView) findViewById(R.id.tvMath);
        tvResult = (TextView) findViewById(R.id.tvResult);

        castingAndSettingClickListener(btnDoubleZero, R.id.btnDoubleZero);
        castingAndSettingClickListener(btnZero, R.id.btnZero);
        castingAndSettingClickListener(btnDot, R.id.btnDot);
        castingAndSettingClickListener(btnEqual, R.id.btnEqual);
        castingAndSettingClickListener(btnOne, R.id.btnOne);
        castingAndSettingClickListener(btnTwo, R.id.btnTwo);
        castingAndSettingClickListener(btnThree, R.id.btnThree);
        castingAndSettingClickListener(btnFour, R.id.btnFour);
        castingAndSettingClickListener(btnFive, R.id.btnFive);
        castingAndSettingClickListener(btnSix, R.id.btnSix);
        castingAndSettingClickListener(btnSeven, R.id.btnSeven);
        castingAndSettingClickListener(btnEight, R.id.btnEight);
        castingAndSettingClickListener(btnNine, R.id.btnNine);
        castingAndSettingClickListener(btnPlus, R.id.btnPlus);
        castingAndSettingClickListener(btnMinus, R.id.btnMinus);
        castingAndSettingClickListener(btnMultiply, R.id.btnMultiply);
        castingAndSettingClickListener(btnDivide, R.id.btnDivide);
        castingAndSettingClickListener(btnBracketOpen, R.id.btnBracketOpen);
        castingAndSettingClickListener(btnBracketEnd, R.id.btnBracketEnd);
        castingAndSettingClickListener(btnC, R.id.btnC);




    }


    void castingAndSettingClickListener(MaterialButton bttn, int id){
        bttn = findViewById(id);
        bttn.setOnClickListener(this);
    }


    @Override
    public void onClick(View view) {


        MaterialButton clickedButton = (MaterialButton) view;

        String buttonText = clickedButton.getText().toString();

        String dataForCalculation = tvMath.getText().toString();

        if (buttonText.equals("C")){
            tvMath.setText("");
            tvResult.setText("0");
            return;
        }else if (buttonText.equals("=")){
            tvMath.setText(tvResult.getText().toString());
            return;
        }else{
            dataForCalculation = dataForCalculation+buttonText;
        }

        tvMath.setText(dataForCalculation);

        String finalResult = makeResult(dataForCalculation);

        if (!finalResult.equals("Error")){
            tvResult.setText(finalResult);
        }


    }



    String makeResult(String data){
        try {
            Context newContext = Context.enter();
            newContext.setOptimizationLevel(-1);
            Scriptable newScriptable = newContext.initStandardObjects();
            String finalResult = newContext.evaluateString(newScriptable, data, "Javascript", 1, null).toString();

            if (finalResult.endsWith(".0")){
                finalResult = finalResult.replace(".0", "");
            }
            return finalResult;
        }catch (Exception e){
            return "Error";
        }
    }


}

Xml Part : 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#F6B6B6"
    android:gravity="bottom"
    android:paddingBottom="15dp"
    android:orientation="vertical"
    tools:context=".MainActivity">


    <TextView
        android:layout_width="match_parent"
        android:id="@+id/tvMath"
        android:layout_marginBottom="20dp"
        android:textSize="30dp"
        android:textColor="@color/black"
        android:paddingHorizontal="40dp"
        android:gravity="right"
        android:layout_height="wrap_content"/>
    <TextView
        android:layout_width="match_parent"
        android:id="@+id/tvResult"
        android:text="0"
        android:layout_marginBottom="20dp"
        android:textSize="60dp"
        android:textColor="@color/black"
        android:paddingHorizontal="40dp"
        android:gravity="right"
        android:layout_height="wrap_content"/>



    <LinearLayout
        android:layout_width="match_parent"
        android:orientation="horizontal"
        android:gravity="center_horizontal"
        android:layout_height="wrap_content">

        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="#0022FF"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="C"
            android:id="@+id/btnC"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/white" />
        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="#0022FF"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="("
            android:id="@+id/btnBracketOpen"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/white" />
        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="#0022FF"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text=")"
            android:id="@+id/btnBracketEnd"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/white" />
        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="#0022FF"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="/"
            android:id="@+id/btnDivide"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/white" />

    </LinearLayout>


    <LinearLayout
        android:layout_width="match_parent"
        android:orientation="horizontal"
        android:gravity="center_horizontal"
        android:layout_height="wrap_content">

        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="@color/white"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="7"
            android:id="@+id/btnSeven"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/black" />
        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="@color/white"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="8"
            android:id="@+id/btnEight"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/black" />
        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="@color/white"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="9"
            android:id="@+id/btnNine"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/black" />
        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="#0022FF"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="*"
            android:id="@+id/btnMultiply"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/white" />

    </LinearLayout>


    <LinearLayout
        android:layout_width="match_parent"
        android:orientation="horizontal"
        android:gravity="center_horizontal"
        android:layout_height="wrap_content">

        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="@color/white"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="4"
            android:id="@+id/btnFour"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/black" />
        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="@color/white"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="5"
            android:id="@+id/btnFive"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/black" />
        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="@color/white"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="6"
            android:id="@+id/btnSix"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/black" />
        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="#0022FF"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="-"
            android:id="@+id/btnMinus"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/white" />

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:orientation="horizontal"
        android:gravity="center_horizontal"
        android:layout_height="wrap_content">

        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="@color/white"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="1"
            android:id="@+id/btnOne"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/black" />
        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="@color/white"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="2"
            android:id="@+id/btnTwo"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/black" />
        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="@color/white"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="3"
            android:id="@+id/btnThree"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/black" />
        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="#0022FF"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="+"
            android:id="@+id/btnPlus"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/white" />

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:orientation="horizontal"
        android:gravity="center_horizontal"
        android:layout_height="wrap_content">

        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="@color/white"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="00"
            android:id="@+id/btnDoubleZero"
            android:layout_margin="10dp"
            android:textSize="22sp"
            android:textColor="@color/black" />
        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="@color/white"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="0"
            android:id="@+id/btnZero"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/black" />
        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="@color/white"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="."
            android:id="@+id/btnDot"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/black" />
        <com.google.android.material.button.MaterialButton
            android:layout_width="70dp"
            android:layout_height="70dp"
            android:backgroundTint="#0022FF"
            app:cornerRadius="35dp"
            style="@style/Widget.MaterialComponents.ExtendedFloatingActionButton"
            android:text="="
            android:id="@+id/btnEqual"
            android:layout_margin="10dp"
            android:textSize="30sp"
            android:textColor="@color/white" />

    </LinearLayout>


</LinearLayout>

Part 9 : Working with Colors and Color Algorithm.

Java Part : 

package first.learn.edittextproject;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.content.ContextCompat;

import android.graphics.Color;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import java.text.DecimalFormat;

public class MainActivity extends AppCompatActivity {

    EditText etTwo,
            etOne;

    TextView tvResult, txtNewResult;
    Button btnPlus, btnMinus, btnDevide, btnMulitiply;

    int grey, sky, red, blue, yellow;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        etTwo = (EditText) findViewById(R.id.etTwo);
        etOne = (EditText) findViewById(R.id.etOne);

        tvResult = (TextView) findViewById(R.id.tvResult);
        btnPlus = (Button) findViewById(R.id.btnPlus);
        btnMinus = (Button)findViewById(R.id.btnMinus);
        btnDevide = (Button)findViewById(R.id.btnDevide);
        btnMulitiply = (Button)findViewById(R.id.btnMulitiply);
        txtNewResult = (TextView)findViewById(R.id.txtNewResult);

/*
yellow: -10752
blue: -16776961
grey: -13291215
sky: -13611010
red: -2818048
 */

        yellow = ContextCompat.getColor(MainActivity.this, R.color.yellow);
      //  btnMinus.setBackgroundColor(-10752);

        blue = Color.BLUE;
       // btnDevide.setBackgroundColor(-16776961);


        grey = Color.parseColor("#353131");
       // btnPlus.setBackgroundColor(-13291215);


        sky = 0xFF304FFE;
       // btnMinus.setBackgroundColor(-2818048);

        red = Color.rgb(213,0,0);
       // btnMulitiply.setBackgroundColor(-2818048);


        System.out.println("yellow: "+yellow+"\nblue: "+blue+"\ngrey: "+grey
        +"\nsky: "+sky+"\nred: "+red);


        btnPlus.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                //changeColorBtnColor(btnPlus);
                changeColorBtnPlus ();
                String a = getTextFromEditText(etOne);

                if (a == null) {

                    return;
                }

                String b = getTextFromEditText(etTwo);

                if (b == null) {
                    return;
                }

                float c = stringToFloat(a);
                float d = stringToFloat(b);

                float e = resultAddFloat(c, d);

               String formatted =  new DecimalFormat("#.####").format(e);
                tvResult.setText("" + formatted);
                txtNewResult.setText("" + formatted);


            }
        });

        btnMinus.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


               // changeColorBtnColor(btnMinus);
                changeColorBtnMinus();

                String a = getTextFromEditText(etOne);

                if (a == null) {

                    return;
                }

                String b = getTextFromEditText(etTwo);

                if (b == null) {
                    return;
                }

                float c = stringToFloat(a);
                float d = stringToFloat(b);


                minus(c, d, tvResult);
                minus(c, d, txtNewResult);


            }
        });

        btnDevide.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

              //changeColorBtnColor(btnDevide);
                changeColorBtnDevide();
                String a = getTextFromEditText(etOne);

                if (a == null) {

                    return;
                }

                String b = getTextFromEditText(etTwo);

                if (b == null) {
                    return;
                }

                float c = stringToFloat(a);
                float d = stringToFloat(b);

                float p = divide( c, d );

                System.out.println("Divide Section: before Formatted : "+ p );

                String formatted =  new DecimalFormat("#.####").format(p);

                System.out.println("Divide Section: after Formatted : "+ formatted );

                tvResult.setText(""+formatted );
                txtNewResult.setText(""+formatted);

            }
        });

        btnMulitiply.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

              //  changeColorBtnColor(btnMulitiply);

                changeColorBtnMultiply();

                String a = getTextFromEditText(etOne);

                if (a == null) {

                    return;
                }

                String b = getTextFromEditText(etTwo);

                if (b == null) {
                    return;
                }

                float c = stringToFloat(a);
                float d = stringToFloat(b);

                multiply (c, d, tvResult );
                multiply (c, d, txtNewResult );

            }
        });

    }

    void changeColorBtnColor(Button btn){

        btnPlus.setBackgroundColor(grey);
        btnMinus.setBackgroundColor(grey);
        btnDevide.setBackgroundColor(grey);
        btnMulitiply.setBackgroundColor(grey);

        btn.setBackgroundColor(red);
    }

    void changeColorBtnPlus (){
        btnPlus.setBackgroundColor(red);
        btnMinus.setBackgroundColor(grey);
        btnDevide.setBackgroundColor(grey);
        btnMulitiply.setBackgroundColor(grey);
    }




    void changeColorBtnMinus (){

        btnPlus.setBackgroundColor(grey);
        btnMinus.setBackgroundColor(red);
        btnDevide.setBackgroundColor(grey);
        btnMulitiply.setBackgroundColor(grey);
    }



    void changeColorBtnDevide (){

        btnPlus.setBackgroundColor(grey);
        btnMinus.setBackgroundColor(grey);
        btnDevide.setBackgroundColor(red);
        btnMulitiply.setBackgroundColor(grey);
    }


    void changeColorBtnMultiply (){

        btnPlus.setBackgroundColor(grey);
        btnMinus.setBackgroundColor(grey);
        btnDevide.setBackgroundColor(grey);
        btnMulitiply.setBackgroundColor(red);
    }

    void  multiply (float a , float b, TextView txtResult ){

        float c = a*b ;
        String formatted =  new DecimalFormat("#.####").format(c);

        txtResult.setText(""+formatted );

    }


    float divide (float n, float m ){

        float x = n/m;

        return  x ;
    }



    void minus (float a , float b, TextView txtResult ){

        float c = a - b;

        String formatted =  new DecimalFormat("#.####").format(c);

        txtResult.setText(""+formatted);

    }

    boolean isIntegerCharacter(String s) {

        int c = -1;

        try {
            c = Integer.parseInt(s);
            return true;
        } catch (NumberFormatException e) {
            return false;
        }
    }

    float stringToFloat(String s) {
        return Float.parseFloat(s);
    }


    float resultAddFloat(float a, float b) {
        return a + b;
    }


    String getTextFromEditText(EditText editText) {
        String s = editText.getText().toString();

        if (TextUtils.isEmpty(s)) {
            editText.setError("Empty");
            return null;
        } else {
            editText.setError(null);
            return s;
        }

    }


}

Xml Part : 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:orientation="vertical"
    android:layout_margin="16dp"

    >



    <EditText
        android:hint="number One...."
        android:layout_marginTop="25dp"
        android:id="@+id/etOne"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="numberDecimal"/>

    <EditText
        android:hint="number two..."
        android:layout_marginTop="25dp"
        android:id="@+id/etTwo"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="numberDecimal"/>


    <TextView
        android:textSize="25dp"
        android:textColor="@color/purple_700"
        android:layout_marginTop="20dp"
        android:id="@+id/tvResult"
        android:gravity="center"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Result..."
        />


   <LinearLayout
       android:layout_marginTop="25dp"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:orientation="horizontal"
       android:weightSum="4">

       <Button
           android:layout_weight="1"
           android:id="@+id/btnPlus"
           android:layout_width="0dp"
           android:layout_height="wrap_content"
           android:text="+"
           android:backgroundTint="@color/grey"/>

       <Button
           android:layout_marginLeft="2dp"
           android:id="@+id/btnMinus"
           android:layout_weight="1"
           android:layout_width="0dp"
           android:layout_height="wrap_content"
           android:text="-"
           android:backgroundTint="@color/grey"/>

       <Button
           android:layout_marginLeft="2dp"
           android:id="@+id/btnDevide"
           android:layout_weight="1"
           android:layout_width="0dp"
           android:layout_height="wrap_content"
           android:text="/"
           android:backgroundTint="@color/grey"/>


       <Button
           android:layout_marginLeft="2dp"
            android:layout_weight="1"
           android:id="@+id/btnMulitiply"
           android:layout_width="0dp"
           android:layout_height="wrap_content"
           android:text="x"
           android:backgroundTint="@color/grey"/>

   </LinearLayout>



    <LinearLayout
        android:layout_marginTop="25dp"
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:orientation="horizontal"
        android:weightSum="4">

        <TextView
            android:background="@color/my_color_red"
            android:layout_width="0dp"
            android:layout_weight="3"
            android:text="Final Resul"
            android:gravity="center"
            android:textColor="@color/white"
            android:layout_height="match_parent"/>

        <TextView
            android:id="@+id/txtNewResult"
            android:background="@color/my_color_green"
            android:layout_width="0dp"
            android:layout_weight="1"
            android:gravity="center"
            android:textColor="@color/white"
            android:text="value"
            android:layout_height="match_parent"/>

    </LinearLayout>










</LinearLayout>

Color.xml : 

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <color name="purple_200">#FFBB86FC</color>
    <color name="purple_500">#FF6200EE</color>
    <color name="purple_700">#FF3700B3</color>
    <color name="teal_200">#FF03DAC5</color>
    <color name="teal_700">#FF018786</color>
    <color name="black">#FF000000</color>
    <color name="white">#FFFFFFFF</color>


    <color name="my_color_red">#B81059</color>

    <color name="my_color_green">#06A120</color>


    <color name="yellow">#FFD600</color>

    <color name="sky">#304FFE</color>

    <color name="blue">#070F40</color>

    <color name="grey">#353131</color>

    <color name="red">#D50000</color>


</resources>