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FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();

fragmentTransaction.add(R.id.frameLayout_fragmentTransaction_fragmentContainer, new FragmentA());
fragmentTransaction2.replace(R.id.frameLayout_fragmentTransaction_fragmentContainer, new FragmentB());
Fragment fragment=getSupportFragmentManager().findFragmentById(
                                              R.id.frameLayout_fragmentTransaction_fragmentContainer);
                if (fragment!=null){
fragmentTransaction3.remove(fragment); 

fragmentTransaction2.addToBackStack(null);
fragmentTransaction.commit();


<FrameLayout
        android:id="@+id/frameLayout_fragmentTransaction_fragmentContainer"

fragment_a.xml

FragmentA.java
class FragmentA extends Fragment
public onCreate
public onCreateView return inflater.inflate(R.layout.fragment_a, container, false);
public onViewCreated

fragment_a.xml 
fragmentA.java
fragment_b.xml
fragmentB.java
FragmentPagerAdapterSample extends FragmentStatePagerAdapter
public FragmentPagerAdapterSample(FragmentManager fm)
getItem(int position) case 0: return new FragmentA();  return null;
getCount() return 3;
getPageTitle(int position) case 0: return "Fragment A";
getPageWidth return 0.8f;

MainActivity.java
ViewPager viewPager = findViewById(R.id.viewPager_viewPagerSample);
viewPager.setAdapter(new FragmentPagerAdapterSample(getSupportFragmentManager()));

TabLayout tabLayout = findViewById(R.id.tabLayout_viewPagerSample);
tabLayout.setupWithViewPager(viewPager);

viewPager.setCurrentItem(1);

dialog_sample.xml
class SampleDialog extends DialogFragment
public Dialog onCreateDialog 

MainActivity.java
SampleDialog sampleDialog = SampleDialog.newInstance("ali");
sampleDialog.show(getSupportFragmentManager(), null);

SampleDialog.java
class SampleDialog extends DialogFragment
public onCreateDialog
AlertDialog.Builder builder = new AlertDialog.Builder(getContext());
View view = LayoutInflater.from(getContext()).inflate(R.layout.dialog_sample, null);
builder.setView(view);

yesBtn = view.findViewById .setOnClickListener
dialogCallback.onNoClicked();
dismiss();
noBtn = view.findViewById .setOnClickListener
dialogCallback.onNoClicked();
dismiss();
return builder.create();

BottomSheetDialogSample.java

class BottomSheetDialogSample extends android.support.design.widget.BottomSheetDialogFragment
public View onCreateView
View view = LayoutInflater.from(getContext()).inflate(R.layout.dialog_sample, container, false);
return view;

<?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"
    android:paddingStart="24dp"
    android:paddingTop="32dp"
    android:paddingEnd="24dp"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/btn_main_fragmentTransactions"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="onClick"
        android:text="Fragment Transactions" />

    <Button
        android:id="@+id/btn_main_viewPager"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="onClick"
        android:text="ViewPager" />

    <Button
        android:id="@+id/btn_main_dialogFragment"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="onClick"
        android:text="Dialog Fragment" />

    <Button
        android:id="@+id/btn_main_bottomSheetFragment"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="onClick"
        android:text="BottomSheet Fragment" />
</LinearLayout>

public class MainActivity extends AppCompatActivity implements View.OnClickListener, SampleDialog.DialogCallback {

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

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.btn_main_fragmentTransactions:
                startActivity(new Intent(this, FragmentTransactionsActivity.class));
                break;

            case R.id.btn_main_viewPager:
                startActivity(new Intent(this, ViewPagerSampleActivity.class));
                break;

            case R.id.btn_main_dialogFragment:
                SampleDialog sampleDialog = SampleDialog.newInstance("ali");
                sampleDialog.show(getSupportFragmentManager(), null);
                break;

            case R.id.btn_main_bottomSheetFragment:
                BottomSheetDialogSample bottomSheetDialogSample=new BottomSheetDialogSample();
                bottomSheetDialogSample.show(getSupportFragmentManager(),null);
                break;
        }
    }


    @Override
    public void onYesClicked() {
        Toast.makeText(this,"On Yes Button Clicked",Toast.LENGTH_LONG).show();
    }

    @Override
    public void onNoClicked() {
        Toast.makeText(this,"On No Button Clicked",Toast.LENGTH_LONG).show();

    }
}

public class FragmentTransactionsActivity extends AppCompatActivity implements View.OnClickListener {

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


    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.btn_fragmentTransactions_add:
                FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
                fragmentTransaction.add(R.id.frameLayout_fragmentTransaction_fragmentContainer, new FragmentA());
                fragmentTransaction.addToBackStack(null);
                fragmentTransaction.commit();
                break;
            case R.id.btn_fragmentTransactions_replace:
                FragmentTransaction fragmentTransaction2 = getSupportFragmentManager().beginTransaction();
                fragmentTransaction2.replace(R.id.frameLayout_fragmentTransaction_fragmentContainer, new FragmentB());
                fragmentTransaction2.addToBackStack(null);
                fragmentTransaction2.commit();
                break;
            case R.id.btn_fragmentTransactions_remove:
                FragmentTransaction fragmentTransaction3 = getSupportFragmentManager().beginTransaction();

                Fragment fragment=getSupportFragmentManager().findFragmentById(R.id.frameLayout_fragmentTransaction_fragmentContainer);
                if (fragment!=null){
                    fragmentTransaction3.remove(fragment);
                    fragmentTransaction3.commit();
                }
                break;
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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=".FragmentTransactionsActivity">

    <FrameLayout
        android:id="@+id/frameLayout_fragmentTransaction_fragmentContainer"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    </FrameLayout>

    <LinearLayout

        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:orientation="horizontal">

        <Button
            android:id="@+id/btn_fragmentTransactions_add"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="onClick"
            android:text="Add" />

        <Button
            android:id="@+id/btn_fragmentTransactions_replace"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="onClick"
            android:text="Replace" />

        <Button
            android:id="@+id/btn_fragmentTransactions_remove"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="onClick"
            android:text="Remove" />
    </LinearLayout>
</RelativeLayout>

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

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="A"
        android:textSize="50sp" />
</FrameLayout>

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

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="B"
        android:textSize="50sp" />
</FrameLayout>

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

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="C"
        android:textSize="50sp" />
</FrameLayout>

public class FragmentA extends Fragment {
    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_a, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
    }


}

package com.sevenlearn.fragmentstutorial;

import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class FragmentB extends Fragment {
    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_b, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
    }
}

public class FragmentC extends Fragment {
    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_c, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    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=".ViewPagerSampleActivity">

<android.support.design.widget.TabLayout
    android:id="@+id/tabLayout_viewPagerSample"
    android:layout_width="match_parent"
    app:tabMode="fixed"
    android:layout_height="56dp">

</android.support.design.widget.TabLayout>

<android.support.v4.view.ViewPager
    android:id="@+id/viewPager_viewPagerSample"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_below="@id/tabLayout_viewPagerSample">

</android.support.v4.view.ViewPager>
</RelativeLayout>

public class ViewPagerSampleActivity extends AppCompatActivity {

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


        ViewPager viewPager = findViewById(R.id.viewPager_viewPagerSample);
        viewPager.setAdapter(new FragmentPagerAdapterSample(getSupportFragmentManager()));

        TabLayout tabLayout = findViewById(R.id.tabLayout_viewPagerSample);
        tabLayout.setupWithViewPager(viewPager);

        viewPager.setCurrentItem(1);

//        viewPager.setOffscreenPageLimit(3);
//        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
//            @Override
//            public void onPageScrolled(int i, float v, int i1) {
//
//            }
//
//            @Override
//            public void onPageSelected(int i) {
//
//            }
//
//            @Override
//            public void onPageScrollStateChanged(int i) {
//
//            }
//        });
    }
}

<?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:padding="16dp"
    android:orientation="vertical">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Lorem ipsum is placeholder text commonly used in the graphic, print, and publishing industries for previewing layouts and visual mockups." />

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

        <Button
            android:id="@+id/btn_dialog_yes"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Yes" />

        <Button
            android:id="@+id/btn_dialog_no"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="No" />
    </LinearLayout>

</LinearLayout>

public class SampleDialog extends DialogFragment {
    private DialogCallback dialogCallback;
    private String name;

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof MainActivity) {
            dialogCallback = (DialogCallback) context;
        }
        name = getArguments().getString("name");
        Toast.makeText(getContext(), name, Toast.LENGTH_SHORT).show();
    }

    @NonNull
    @Override
    public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {

        AlertDialog.Builder builder = new AlertDialog.Builder(getContext());
        View view = LayoutInflater.from(getContext()).inflate(R.layout.dialog_sample, null);
        builder.setView(view);

        Button yesBtn = view.findViewById(R.id.btn_dialog_yes);
        yesBtn.setOnClickListener( new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                dialogCallback.onYesClicked();
                dismiss();
            }
        });

        Button noBtn = view.findViewById(R.id.btn_dialog_no);
        noBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                dialogCallback.onNoClicked();
                dismiss();
            }
        });
        return builder.create();
    }

    public static SampleDialog newInstance(String name) {

        Bundle args = new Bundle();
        args.putString("name", name);
        SampleDialog fragment = new SampleDialog();
        fragment.setArguments(args);
        return fragment;
    }

    interface DialogCallback {
        void onYesClicked();

        void onNoClicked();
    }
}

public class FragmentPagerAdapterSample extends FragmentStatePagerAdapter {
    public FragmentPagerAdapterSample(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        switch (position) {
            case 0:
                return new FragmentA();
            case 1:
                return new FragmentB();
            case 2:
                return new FragmentC();
        }
        return null;
    }

    @Override
    public int getCount() {
        return 3;
    }

    @Nullable
    @Override
    public CharSequence getPageTitle(int position) {
        switch (position) {
            case 0:
                return "Fragment A";
            case 1:
                return "Fragment B";
            case 2:
                return "Fragment C";
        }
        return null;
    }

    @Override
    public float getPageWidth(int position) {
        return 0.8f;
    }
}

public class BottomSheetDialogSample extends android.support.design.widget.BottomSheetDialogFragment {
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = LayoutInflater.from(getContext()).inflate(R.layout.dialog_sample, container, false);
        return view;
    }
}