Moving between fragments

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This post describes how open different fragments from a menu fragment in an Activity.

Create a new empty project in Android Studio. Create your layout in activity_main.xml. Add a FrameLayout here.

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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">

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/frame1"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

Add menu_fragment.xml with four buttons.

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#aafccc">

    <Button
        android:id="@+id/button1"
        android:layout_width="120dp"
        android:layout_height="100dp"
        android:text="ADD"
        android:textStyle="bold"
        android:backgroundTint="#ff5555"
        app:layout_constraintBottom_toTopOf="@+id/button3"
        app:layout_constraintEnd_toStartOf="@+id/button2"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button2"
        android:layout_width="120dp"
        android:layout_height="100dp"
        android:text="SUBTRACT"
        android:textStyle="bold"
        android:backgroundTint="#ff55ff"
        app:layout_constraintBottom_toTopOf="@+id/button3"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@+id/button1"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button3"
        android:layout_width="120dp"
        android:layout_height="100dp"
        android:text="Multiply"
        android:textStyle="bold"
        android:backgroundTint="#5599ff"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/button4"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/button1" />

    <Button
        android:id="@+id/button4"
        android:layout_width="120dp"
        android:layout_height="100dp"
        android:text="DIVIDE"
        android:textStyle="bold"
        android:backgroundTint="#999955"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@+id/button3"
        app:layout_constraintTop_toBottomOf="@id/button2" />
</androidx.constraintlayout.widget.ConstraintLayout>

Add MenuFragment.java use following codes. In on click events of button1, button2, button3, and button4, we display AddFragment, SubtractFragment, MultiplyFragment and DivideFragment respectively.

package com.example.mathfragments;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentTransaction;

public class MenuFragment extends Fragment {

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.menu_fragment, container, false);

        Button button1 = v.findViewById(R.id.button1);
        Button button2 = v.findViewById(R.id.button2);
        Button button3 = v.findViewById(R.id.button3);
        Button button4 = v.findViewById(R.id.button4);

        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FragmentTransaction transaction = getActivity().getSupportFragmentManager().beginTransaction();
                Fragment fragment = new AddFragment();
                transaction.replace(R.id.frame1, fragment, "add");
                transaction.addToBackStack(null).commit();
            }
        });

        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FragmentTransaction transaction = getActivity().getSupportFragmentManager().beginTransaction();
                Fragment fragment = new SubtractFragment();
                transaction.replace(R.id.frame1, fragment, "subtract");
                transaction.addToBackStack(null).commit();
            }
        });

        button3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FragmentTransaction transaction = getActivity().getSupportFragmentManager().beginTransaction();
                Fragment fragment = new MultiplyFragment();
                transaction.replace(R.id.frame1, fragment, "multiply");
                transaction.addToBackStack(null).commit();
            }
        });

        button4.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FragmentTransaction transaction = getActivity().getSupportFragmentManager().beginTransaction();
                Fragment fragment = new DivideFragment();
                transaction.replace(R.id.frame1, fragment, "divide");
                transaction.addToBackStack(null).commit();
            }
        });

        return v;
    }
}

Create add_fragment.xml.

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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="#ff5555">

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Addition"
        android:textStyle="bold"
        android:textSize="24sp"
        android:textColor="@color/white"
        app:layout_constraintBottom_toTopOf="@id/editTextNumberDecimal"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"/>

    <EditText
        android:id="@+id/editTextNumberDecimal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:textSize="20sp"
        android:inputType="numberDecimal"
        android:background="#eeeeff"
        android:padding="8dp"
        app:layout_constraintBottom_toTopOf="@+id/textView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView1" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="+"
        android:textColor="@color/white"
        android:textStyle="bold"
        android:textSize="24sp"
        app:layout_constraintBottom_toTopOf="@+id/editTextNumberDecimal2"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editTextNumberDecimal" />

    <EditText
        android:id="@+id/editTextNumberDecimal2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:textSize="20sp"
        android:background="#eeeeff"
        android:padding="8dp"
        android:inputType="numberDecimal"
        app:layout_constraintBottom_toTopOf="@+id/button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/editTextNumberDecimal"/>

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="ADD"
        android:textSize="20sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="0.00"
        android:textColor="@color/white"
        android:textStyle="bold"
        android:textSize="24sp"
        app:layout_constraintBottom_toTopOf="@id/button2"
        app:layout_constraintTop_toBottomOf="@id/button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"/>

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="BACK"
        android:textSize="20sp"
        app:layout_constraintTop_toBottomOf="@id/textView2"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

Create AddFragment.java.

package com.example.mathfragments;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;

public class AddFragment extends Fragment {

    FragmentManager fm;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.add_fragment, null);

        EditText edit1 = v.findViewById(R.id.editTextNumberDecimal);
        EditText edit2 = v.findViewById(R.id.button);
        Button button2 = v.findViewById(R.id.editTextNumberDecimal2);
        Button button1 = v.findViewById(R.id.button2);
        TextView text2 = v.findViewById(R.id.textView2);

        fm = getActivity().getSupportFragmentManager();

        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                double a = Double.parseDouble(edit1.getText().toString());
                double b = Double.parseDouble(edit2.getText().toString());
                double c = a+b;
                text2.setText(c + "");
            }
        });

        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                fm.beginTransaction().remove(fm.findFragmentByTag("add")).commit();
                fm.popBackStackImmediate();
            }
        });


        return v;
    }
}

Create subtract_fragment.xml. 

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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="#ff55ff">

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Subtraction"
        android:textStyle="bold"
        android:textSize="24sp"
        android:textColor="@color/white"
        app:layout_constraintBottom_toTopOf="@id/editTextNumberDecimal"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"/>

    <EditText
        android:id="@+id/editTextNumberDecimal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:textSize="20sp"
        android:inputType="numberDecimal"
        android:background="#eeeeff"
        android:padding="8dp"
        app:layout_constraintBottom_toTopOf="@+id/textView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView1" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="-"
        android:textColor="@color/white"
        android:textStyle="bold"
        android:textSize="24sp"
        app:layout_constraintBottom_toTopOf="@+id/editTextNumberDecimal2"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editTextNumberDecimal" />

    <EditText
        android:id="@+id/editTextNumberDecimal2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:textSize="20sp"
        android:background="#eeeeff"
        android:padding="8dp"
        android:inputType="numberDecimal"
        app:layout_constraintBottom_toTopOf="@+id/button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/editTextNumberDecimal"/>

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="SUBTRACT"
        android:textSize="20sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="0.00"
        android:textColor="@color/white"
        android:textStyle="bold"
        android:textSize="24sp"
        app:layout_constraintBottom_toTopOf="@id/button2"
        app:layout_constraintTop_toBottomOf="@id/button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"/>

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="BACK"
        android:textSize="20sp"
        app:layout_constraintTop_toBottomOf="@id/textView2"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

Create SubtractFragment.java. 

package com.example.mathfragments;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;

public class SubtractFragment extends Fragment {

    FragmentManager fm;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.subtract_fragment, null);

        EditText edit1 = v.findViewById(R.id.editTextNumberDecimal);
        EditText edit2 = v.findViewById(R.id.editTextNumberDecimal2);
        Button button1 = v.findViewById(R.id.button);
        Button button2 = v.findViewById(R.id.button2);
        TextView text2 = v.findViewById(R.id.textView2);

        fm = getActivity().getSupportFragmentManager();

        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                double a = Double.parseDouble(edit1.getText().toString());
                double b = Double.parseDouble(edit2.getText().toString());
                double c = a-b;
                text2.setText(c+"");
            }
        });

        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                fm.beginTransaction().remove(fm.findFragmentByTag("subtract")).commit();
                fm.popBackStackImmediate();
            }
        });


        return v;
    }
}

Create multiply_fragment.xml. 

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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="#5599ff">

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Multiplication"
        android:textStyle="bold"
        android:textSize="24sp"
        android:textColor="@color/white"
        app:layout_constraintBottom_toTopOf="@id/editTextNumberDecimal"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"/>

    <EditText
        android:id="@+id/editTextNumberDecimal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:textSize="20sp"
        android:inputType="numberDecimal"
        android:background="#eeeeff"
        android:padding="8dp"
        app:layout_constraintBottom_toTopOf="@+id/textView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView1" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="*"
        android:textColor="@color/white"
        android:textStyle="bold"
        android:textSize="24sp"
        app:layout_constraintBottom_toTopOf="@+id/editTextNumberDecimal2"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editTextNumberDecimal" />

    <EditText
        android:id="@+id/editTextNumberDecimal2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:textSize="20sp"
        android:background="#eeeeff"
        android:padding="8dp"
        android:inputType="numberDecimal"
        app:layout_constraintBottom_toTopOf="@+id/button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/editTextNumberDecimal"/>

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="MULTIPLY"
        android:textSize="20sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="0.00"
        android:textColor="@color/white"
        android:textStyle="bold"
        android:textSize="24sp"
        app:layout_constraintBottom_toTopOf="@id/button2"
        app:layout_constraintTop_toBottomOf="@id/button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"/>

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="BACK"
        android:textSize="20sp"
        app:layout_constraintTop_toBottomOf="@id/textView2"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

Create MultiplyFragment.java. 

package com.example.mathfragments;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;

public class MultiplyFragment extends Fragment {

    FragmentManager fm;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.multiply_fragment, null);

        EditText edit1 = v.findViewById(R.id.editTextNumberDecimal);
        EditText edit2 = v.findViewById(R.id.editTextNumberDecimal2);
        Button button1 = v.findViewById(R.id.button);
        Button button2 = v.findViewById(R.id.button2);
        TextView text2 = v.findViewById(R.id.textView2);

        fm = getActivity().getSupportFragmentManager();

        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                double a = Double.parseDouble(edit1.getText().toString());
                double b = Double.parseDouble(edit2.getText().toString());
                double c = a*b;
                text2.setText(c+"");
            }
        });

        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                fm.beginTransaction().remove(fm.findFragmentByTag("multiply")).commit();
                fm.popBackStackImmediate();
            }
        });

        return v;
    }
}

Create divide_fragment.xml. 

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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="#999955">

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Division"
        android:textStyle="bold"
        android:textSize="24sp"
        android:textColor="@color/white"
        app:layout_constraintBottom_toTopOf="@id/editTextNumberDecimal"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"/>

    <EditText
        android:id="@+id/editTextNumberDecimal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:textSize="20sp"
        android:inputType="numberDecimal"
        android:background="#eeeeff"
        android:padding="8dp"
        app:layout_constraintBottom_toTopOf="@+id/textView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView1" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="/"
        android:textColor="@color/white"
        android:textStyle="bold"
        android:textSize="24sp"
        app:layout_constraintBottom_toTopOf="@+id/editTextNumberDecimal2"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editTextNumberDecimal" />

    <EditText
        android:id="@+id/editTextNumberDecimal2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:textSize="20sp"
        android:background="#eeeeff"
        android:padding="8dp"
        android:inputType="numberDecimal"
        app:layout_constraintBottom_toTopOf="@+id/button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/editTextNumberDecimal"/>

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="DIVIDE"
        android:textSize="20sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="0.00"
        android:textColor="@color/white"
        android:textStyle="bold"
        android:textSize="24sp"
        app:layout_constraintBottom_toTopOf="@id/button2"
        app:layout_constraintTop_toBottomOf="@id/button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"/>

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="BACK"
        android:textSize="20sp"
        app:layout_constraintTop_toBottomOf="@id/textView2"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

Create DivideFragment.java. 

package com.example.mathfragments;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;

public class DivideFragment extends Fragment {

    FragmentManager fm;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.divide_fragment, null);

        EditText edit1 = v.findViewById(R.id.editTextNumberDecimal);
        EditText edit2 = v.findViewById(R.id.editTextNumberDecimal2);
        Button button1 = v.findViewById(R.id.button);
        Button button2 = v.findViewById(R.id.button2);
        TextView text2 = v.findViewById(R.id.textView2);

        fm = getActivity().getSupportFragmentManager();

        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                double a = Double.parseDouble(edit1.getText().toString());
                double b = Double.parseDouble(edit2.getText().toString());
                double c = a/b;
                text2.setText(c+"");
            }
        });

        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                fm.beginTransaction().remove(fm.findFragmentByTag("divide")).commit();
                fm.popBackStackImmediate();
            }
        });


        return v;
    }
}

In MainActivity.java use following codes.

package com.example.mathfragments;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentTransaction;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

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

        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        Fragment fragment = new MenuFragment();
        transaction.replace(R.id.frame1, fragment);
        transaction.commit();
    }
}

Now run the app.

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