Source to display character array with numberPicker in Android studio (Java)

As the title says. Since it is a memo for myself, I will omit the explanation. There were many places where I got stuck, so I hope it will be useful and I will share it.

Development environment: Android Studio 3.1.3 (Mac) Language: java

MainActivity.java

package com.example.ktakeda.numberpicker;

import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.NumberPicker;
import android.widget.TextView;

import android.content.res.Resources;

import java.lang.reflect.Array;
import java.util.Arrays;
import java.util.List;

import static com.example.ktakeda.numberpicker.R.array;

public class MainActivity extends Activity {

    NumberPicker numPicker;
    Button button1;
    TextView textView1;

    //Within initViews, strings.Change to read from xml
    // final String[] pref = {"tokyo", "chiba", "kanagawa"};


    //Generate view?
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        findViews();
        initViews();
    }
    //Get element of v
    private void findViews(){
        numPicker = (NumberPicker)findViewById(R.id.numPicker);
        button1 = (Button)findViewById(R.id.button1);
        textView1 = (TextView)findViewById(R.id.textView1);
    }

    //processing
    private void initViews(){

        // getResources
        Resources res = getResources();
        final String[] pref = res.getStringArray(R.array.pref_array);

        //Put null first, prevent the app from crashing
        numPicker.setDisplayedValues(null);
        //Setting
        numPicker.setDisplayedValues(pref);
        numPicker.setMinValue(1);
        numPicker.setMaxValue(pref.length);


        button1.setOnClickListener(new OnClickListener(){
            //Are you there?
            @Override
            public void onClick(View v) {
                int idx  = numPicker.getValue();
                textView1.setText(pref[idx - 1]);
            }
        });
    }
}

activity_main.xml

<?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"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:layout_gravity="center"
        android:textSize="30dp"/>

    <NumberPicker
        android:id="@+id/numPicker"
        android:layout_width="200sp"
        android:layout_height="wrap_content"
        android:layout_gravity="center"/>

    <Button
        android:id="@+id/button1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="OK"/>

</LinearLayout>

strings.xml

<resources>
    <string name="app_name">numberPicker</string>
    <string-array name="pref_array">
        <item>Tokyo</item>
        <item>Kanagawa</item>
        <item>Chiba</item>
        <item>Okinawa</item>
    </string-array>
</resources>