The Android app just clicks on the button and it falls off.

java.lang.NullPointerException: Attempt to invoice virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on an all object reference

package com.example.tokoroshingo.myapplication;
import android.content.Intent;
import android.content.res.Resources;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.content.Context;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
public class FileActivity1 extensions AppCompatActivity{
    private TextView textView;
    privateEditTexteditText;
    private String fileName[] = new String[15];
    private inti;
    private Button Button Read [] = new Button [15];

    @ Override
    protected void onCreate (Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_file1);

        textView=findViewById(R.id.text_view);

        for(i=0;i<15;i++){
            fileName[i]="CH1_"+i+1+".txt";
            int viewId;
            String resViewName;
            resViewName = "button_ch" + i+1;
            viewId=getResources().getIdentifier(resViewName, "id", getPackageName());
            buttonRead[i] = findViewById(viewId);
            buttonRead[i].setOnClickListener(newView.OnClickListener(){
                @ Override
                public void onClick (View v) {
                    String str = readFile(fileName[i]);
                    if(str!=null){
                        textView.setText(str);
                    } else{
                        textView.setText(R.string.read_error);
                    }
                    TextView textReceive1=(TextView) findViewById (R.id.text_view1);
                    textReceive1.setText("CH"+i);
                }
            });

        }

        //  editText=findViewById(R.id.edit_text);

        Button return_file_Button1 = findViewById (R.id.return_file_button1);
        return_file_Button1.setOnClickListener(newView.OnClickListener(){
            @ Override
            public void onClick (View v) {
                Intent=new Intent(getApplication(), SubActivity5.class);
                startActivity (intent);
            }
        });

    }

    // Read the file
    public String readFile (String file) {
        String text = null;

        try{
            FileInputStream in=openFileInput(file);
            BufferedReader reader = new BufferedReader (new InputStreamReader(in, "UTF-8"));
            String str="";
            String tmp;
            while((tmp=read.readLine())!=null){
                str = str + tmp + "\n";
            }
            text = str;
            reader.close();
        } catch(IOExceptione){
            e.printStackTrace();
        }
        return text;
    }
}