main
package com.example.admin.s20172296_0910_03;

import android.os.Environment;
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.Toast;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.PrintWriter;

public class MainActivity extends AppCompatActivity {
    EditText edit;
    File file;
    File path;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        path= Environment.getExternalStoragePublicDirectory(
                Environment.DIRECTORY_DOWNLOADS);
        file=new File(path,"test.txt");
        
        String state=Environment.getExternalStorageState();
        if(state.equals(Environment.MEDIA_MOUNTED)==false){
            Toast.makeText(getApplicationContext(),"¿ÜºÎ ½ºÅ丮Áö ½ÇÆÐ",
                    Toast.LENGTH_SHORT).show();
        }
        edit=(EditText)findViewById(R.id.EditText01);
        final Button readButton=(Button)findViewById(R.id.read);
        Button writeButton=(Button)findViewById(R.id.write);
        
        readButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    FileReader in = new FileReader(file);
                    StringBuffer buffer = new StringBuffer();
                    BufferedReader reader = new BufferedReader(in);
                    String str = reader.readLine();
                    while (str != null) {
                        buffer.append(str + "|n");
                        str = reader.readLine();
                    }
                    edit.setText(new String(buffer));
                    reader.close();
                    Toast.makeText(getApplicationContext(), "Read",
                            Toast.LENGTH_LONG).show();
                }catch (Exception e){
                    e.printStackTrace();
                    Toast.makeText(getApplicationContext(),"Read Field",
                            Toast.LENGTH_LONG).show();
                    
                }
            }
        });
        writeButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try{
                    FileWriter wr=new FileWriter(file,false);
                    PrintWriter writer=new PrintWriter(wr);
                    writer.print(edit.getText().toString());
                    writer.close();
                    Toast.makeText(getApplicationContext(),"Write",
                            Toast.LENGTH_LONG).show();
                }catch (Exception e){
                    e.printStackTrace();
                    Toast.makeText(getApplicationContext(),"Write Field",
                            Toast.LENGTH_LONG).show();
                }
            }
        });
    }
}