get a sorted list of directories

app/src/main/java/com/simplemobiletools/filemanager/activities/MainActivity.java

@@ -0,0 +1,40 @@
+package com.simplemobiletools.filemanager.activities;
+
+import android.os.Bundle;
+import android.os.Environment;
+import android.support.v7.app.AppCompatActivity;
+
+import com.simplemobiletools.filemanager.R;
+import com.simplemobiletools.filemanager.Utils;
+import com.simplemobiletools.filemanager.models.Directory;
+
+import java.io.File;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class MainActivity extends AppCompatActivity {
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_main);
+        List<Directory> dirs = getDirectories();
+        Collections.sort(dirs);
+    }
+
+    private List<Directory> getDirectories() {
+        final List<Directory> dirs = new ArrayList<>();
+        final String path = Environment.getExternalStorageDirectory().toString();
+        final File root = new File(path);
+        File[] files = root.listFiles();
+        for (File file : files) {
+            if (file.isDirectory()) {
+                final String dirPath = file.getAbsolutePath();
+                final String dirName = Utils.getFilename(dirPath);
+                dirs.add(new Directory(dirPath, dirName));
+            }
+        }
+        return dirs;
+    }
+}