Informasi tidak disimpan setelah peralihan tampilan menggunakan Intents (android)

Saya menggunakan Intents untuk mengganti tampilan di aplikasi pencatatan skor bola basket 2 tampilan saya yang sederhana. Halaman pertama dan utama adalah halaman yang menyimpan skor, dan halaman kedua adalah halaman yang menampung 5 pemain (5 EditTexts). Semuanya berfungsi tetapi skor dan susunan pemain tidak menyimpan informasinya setelah tampilan dialihkan. Misalnya skor diatur menjadi 7-0, pengguna masuk ke halaman susunan pemain dan memperbaruinya dengan nama pemain, kemudian pengguna kembali ke halaman pencatatan skor dan skor menjadi 0-0. Saya memahami bahwa fragmen mungkin menyelesaikan masalah ini tetapi saya tidak tahu cara menerapkan fragmen (walaupun saya telah membaca dokumentasi beberapa kali), jadi bantuan terbaik yang dapat diberikan kepada saya adalah contoh spesifik tentang apa yang perlu saya ubah. Kode saya diposting di bawah, dan terima kasih banyak atas bantuannya.

//////////MainActivity.java (score keeping view)//////

package com.example.ryan.basketballscorekeeper;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.ViewGroup;
import android.content.Intent;

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

    Button lineupButton= (Button) findViewById(R.id.lineup_button);

        lineupButton.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) {
                Intent intent = new Intent(MainActivity.this,       Main2Activity.class);
                startActivity(intent);
            }

        });
    TextView textView = (TextView) findViewById(R.id.homeTeamScore);
    textView.setText(homeScore+"");
    TextView textView2 = (TextView) findViewById(R.id.awayTeamScore);
    textView.setText(awayScore+"");



}


int homeScore=0; //home team score
int awayScore=0; //away team score
String awayScoreString=awayScore+"";
String homeScoreString=homeScore+"";



public void onSaveInstanceState(Bundle savedInstanceState) {
    super.onSaveInstanceState(savedInstanceState);
}

public void onRestoreInstanceState(Bundle savedInstanceState) {
    super.onSaveInstanceState(savedInstanceState);
}

public void onStart(Bundle savedInstanceState){
    setContentView(R.layout.activity_main);
    onRestoreInstanceState(savedInstanceState);
}

public void onPause (Bundle savedInstanceState){
    onSaveInstanceState(savedInstanceState);
}
public void onDestroy (Bundle savedInstanceState){
    onSaveInstanceState(savedInstanceState);
}

public void lineupsView(View view){
    Intent intent = new Intent(this, Main2Activity.class);
    setContentView(R.layout.lineups);

}

public void mainView(View view){
    setContentView(R.layout.activity_main);
}

  ///////////////beginning of score-updating code////////////////

public void updateStrings(){
    homeScoreString=homeScore+"";
    awayScoreString=awayScore+"";
}

public void threePointerAway(View view){
    TextView textView = (TextView) findViewById(R.id.awayTeamScore);
    awayScore+=3;
    updateStrings();
    textView.setText(awayScoreString);
}
public void threePointerHome(View view){
    TextView textView = (TextView) findViewById(R.id.homeTeamScore);
    homeScore+=3;
    updateStrings();
    textView.setText(homeScoreString);
}
public void twoPointerHome(View view){
    TextView textView = (TextView) findViewById(R.id.homeTeamScore);
    homeScore+=2;
    updateStrings();
    textView.setText(homeScoreString);
}
public void twoPointerAway(View view){
    TextView textView = (TextView) findViewById(R.id.awayTeamScore);
    awayScore+=2;
    updateStrings();
    textView.setText(awayScoreString);
}
public void freeThrowHome(View view){
    TextView textView = (TextView) findViewById(R.id.homeTeamScore);
    homeScore+=1;
    updateStrings();
    textView.setText(homeScoreString);
}
public void freeThrowAway(View view){
    TextView textView = (TextView) findViewById(R.id.awayTeamScore);
    awayScore+=1;
    updateStrings();
    textView.setText(awayScoreString);
}

public void reset(View view){
    TextView awayView = (TextView) findViewById(R.id.awayTeamScore);
    TextView homeView = (TextView) findViewById(R.id.homeTeamScore);
    homeScore=0;
    awayScore=0;
    updateStrings();
    awayView.setText(awayScoreString);
    homeView.setText(homeScoreString);
}


}
 ///////activity_main.xml (score keeping xml file)//////

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout       xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.ryan.basketballscorekeeper.MainActivity"

>

<ImageView
    android:layout_width="match_parent"
   android:layout_height="match_parent"
    android:src="@drawable/bballcourt"
    android:scaleType="centerCrop"
    />


<LinearLayout

    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    >
    <LinearLayout
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:layout_gravity="center"
        android:orientation="vertical"
        >

        <TextView
            android:textColor="#ffffff"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Home Team"
            android:layout_margin="10dp"
            android:layout_gravity="center"
            android:textSize="15dp"
            />
        <TextView
            android:textColor="#ffffff"
            android:id="@+id/homeTeamScore"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="0"
            android:textSize="50dp"
            android:layout_gravity="center"
            />
        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="+3 Points"
            android:background="#ffbf80"
            android:layout_gravity="center"
            android:onClick="threePointerHome"
            android:layout_marginTop="20dp"
            android:textSize="20dp"
            android:padding="10dp"
            />
        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="+2 Points"
            android:background="#ffbf80"
            android:layout_gravity="center"
            android:onClick="twoPointerHome"
            android:layout_marginTop="20dp"
            android:textSize="20dp"
            android:padding="10dp"
            />
        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Free Throw"
            android:background="#ffbf80"
            android:layout_gravity="center"
            android:onClick="freeThrowHome"
            android:layout_marginTop="20dp"
            android:textSize="17dp"
            android:padding="10dp"
            />
    </LinearLayout>

    <View
        android:layout_width="5dp"
        android:layout_height="340dp"
        android:background="#d9d9d9"
        android:layout_marginTop="40dp"

        />

    <LinearLayout
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:layout_gravity="center"
        android:orientation="vertical"
        >

        <TextView
            android:textColor="#ffffff"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Away Team"
            android:layout_margin="10dp"
            android:layout_gravity="center"
            android:textSize="15dp"
            />
        <TextView
            android:textColor="#ffffff"
            android:id="@+id/awayTeamScore"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="0"
            android:textSize="50dp"
            android:layout_gravity="center"
            />
        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="+3 Points"
            android:background="#ffbf80"
            android:layout_gravity="center"
            android:onClick="threePointerAway"
            android:layout_marginTop="20dp"
            android:textSize="20dp"
            android:padding="10dp"
            />
        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="+2 Points"
            android:background="#ffbf80"
            android:layout_gravity="center"
            android:onClick="twoPointerAway"
            android:layout_marginTop="20dp"
            android:textSize="20dp"
            android:padding="10dp"
            />
        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Free Throw"
            android:background="#ffbf80"
            android:layout_gravity="center"
            android:onClick="freeThrowAway"
            android:layout_marginTop="20dp"
            android:textSize="17dp"
            android:padding="10dp"
            />
    </LinearLayout>

 </LinearLayout>

 <Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="reset"
    android:textAllCaps="true"
    android:layout_centerHorizontal="true"
    android:layout_alignParentBottom="true"
    android:padding="15dp"
    android:layout_marginBottom="40dp"
    android:textSize="20dp"
    android:background="#ffbf80"
    android:onClick="reset"

    />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Lineups"
    android:textAllCaps="true"
    android:layout_alignParentRight="true"
    android:layout_alignParentBottom="true"
    android:padding="15dp"
    android:layout_margin="10dp"
    android:textSize="20dp"
    android:background="#ff8000"
    android:id="@+id/lineup_button" />

</RelativeLayout>


///////Main2Activity.java (lineup view)//////


  package com.example.ryan.basketballscorekeeper;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class Main2Activity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main2);

    Button mainButton= (Button) findViewById(R.id.main_button);

    mainButton.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View view) {
            Intent intent = new Intent(Main2Activity.this,    MainActivity.class);
            startActivity(intent);
        }

    });

    EditText editText1 = (EditText) findViewById(R.id.one);
    one=editText1.getText().toString();
    EditText editText2 = (EditText) findViewById(R.id.two);
    two=editText1.getText().toString();
    EditText editText3 = (EditText) findViewById(R.id.three);
    three=editText1.getText().toString();
    EditText editText4 = (EditText) findViewById(R.id.four);
    four=editText1.getText().toString();
    EditText editText5 = (EditText) findViewById(R.id.five);
    five=editText1.getText().toString();

}
String one,two,three,four,five; //this represents the five players
}

////////activity_main2.xml (lineup view xml file)///////
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout   xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.ryan.basketballscorekeeper.Main2Activity"
android:orientation="vertical"
>

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <ImageView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:src="@drawable/bballcourt"
        android:scaleType="centerCrop"
        />

    <TextView
        android:id="@+id/lineups"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="#ffffff"
        android:text="Lineups"
        android:textSize="30dp"
        android:padding="30dp"
        />

    <EditText
        android:textColor="#ffffff"
        android:id="@+id/one"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textNoSuggestions"
        android:maxLines="1"
        android:layout_below="@id/lineups"
        />
    <EditText
        android:textColor="#ffffff"
        android:id="@+id/two"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textNoSuggestions"
        android:maxLines="1"
        android:layout_below="@id/one"
        />
    <EditText
        android:textColor="#ffffff"
        android:id="@+id/three"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textNoSuggestions"
        android:maxLines="1"
        android:layout_below="@id/two"
        />
    <EditText
        android:textColor="#ffffff"
        android:id="@+id/four"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textNoSuggestions"
        android:maxLines="1"
        android:layout_below="@id/three"
        />
    <EditText
        android:textColor="#ffffff"
        android:id="@+id/five"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textNoSuggestions"
        android:maxLines="1"
        android:layout_below="@id/four"
        />
    <Button
        android:id="@+id/main_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Score"
        android:textAllCaps="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentBottom="true"
        android:padding="15dp"
        android:layout_margin="10dp"
        android:textSize="20dp"
        android:background="#ff8000"

        />
    </RelativeLayout>

</LinearLayout>