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package com.example.admin.s20172296_0910_02;

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 java.io.File;

public class MainActivity extends AppCompatActivity {

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

        Button btn;
        final EditText edt;
        btn=(Button)findViewById(R.id.btn);
        edt=(EditText)findViewById(R.id.edt);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String sysDir= Environment.getRootDirectory()
                        .getAbsolutePath();
                File[]sysFiles=(new File(sysDir).listFiles());

                String strFname;
                for(int i=0;i<sysFiles.length;i++){
                    if(sysFiles[i].isDirectory()==true)
                        strFname=" <Æú´õ>"+sysFiles[i].toString();
                    else
                        strFname="<ÆÄÀÏ>"+sysFiles[i].toString();

                    edt.setText(edt.getText()+"\n"+strFname);
                }
            }
        });
    }
}


ac
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/btn"
        android:text="½Ã½ºÅÛ Æú´õ ¹× ÆÄÀÏ ¸ñ·Ï º¸±â"/>

    <EditText
        android:layout_width="match_parent"
        android:layout_height= "wrap_content"
        android:id="@+id/edt"/>

</LinearLayout>