class MainActivity

package com.example.choi.mystudy25_2;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.io.InputStream;

public class MainActivity extends AppCompatActivity {

    final static String TAG="MainActivity";

    Button btnIn;
    TextView tvIn;


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

        btnIn=(Button)findViewById(R.id.bt_in);
        tvIn=(TextView)findViewById(R.id.tv_in);



        btnIn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                InputStream is =null;
                try{
                    is=getResources().openRawResource(R.raw.reex);
                    byte[] data=new byte[is.available()];
                    while (is.read(data)!=-1){
                    }
                    tvIn.setText(new String(data));
                }catch (Exception e){
                    e.printStackTrace();
                }finally {
                    try {
                        if(is!=null)is.close();
                    }catch (Exception e2){
                        e2.printStackTrace();
                    }
                }

            }
        });



    }



}

 

R.layout.activity_main

<?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:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.choi.mystudy25_2.MainActivity">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        android:id="@+id/tv_in"
        android:textStyle="normal|bold"
        android:textAlignment="textStart"
        android:textSize="14sp" />

    <Button
        android:text="data in"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/bt_in"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />


</RelativeLayout>