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Questions and Answers

What is the purpose of the getExternalFilesDir method?

To list all the files in the internal storage

To read data from the internal storage

To return a public directory for common files like photos, music, etc.

To return a private external directory for your app with the given name (correct)

What is the return type of the getExternalFilesDir and Environment.getExternalStoragePublicDirectory methods?

java.io.FileInputStream

java.io.FileDescriptor

java.io.File (correct)

java.io.FileNotFoundException

What is the purpose of the Environment.getExternalStoragePublicDirectory method?

To return a private external directory for your app with a given name

To list all the files in the internal storage

To read data from the internal storage

To return a public directory for common files like photos, music, etc. (correct)

What is the parameter of the getExternalFilesDir method?

null or a name Signup and view all the answers

What is the purpose of the PrintStream class in the example code?

To write data to the file Signup and view all the answers

What is the purpose of the listFiles method in the example code?

To list all the files in the directory Signup and view all the answers

What is the primary purpose of the internal storage in Android?

To store files that are private to each app Signup and view all the answers

What is the primary function of the java.io.File class in Android?

To represent a file or directory Signup and view all the answers

What is the purpose of the getFilesDir() method in Android?

To return internal directory for your app Signup and view all the answers

What is the purpose of the openFileInput() method in Android?

To open a file for reading Signup and view all the answers

What is the purpose of the java.io.InputStream class in Android?

To represent a flow of data bytes from a source or destination Signup and view all the answers

What is the primary difference between internal and external storage in Android?

Internal storage is private to each app, while external storage is shared Signup and view all the answers

What happens to files stored in internal storage when an app is uninstalled?

The files are wiped out Signup and view all the answers

What is the primary purpose of the java.io.OutputStream class in Android?

To represent a flow of data bytes to a source or destination Signup and view all the answers

What type of objects do some methods return to read/write files?

java.io.InputStream or OutputStream Signup and view all the answers

What is the purpose of the openRawResource method in the example?

To read a file from the res/raw directory Signup and view all the answers

What is the purpose of the MODE_PRIVATE parameter in the openFileOutput method?

To indicate the file is private to the app Signup and view all the answers

What is a characteristic of internal storage?

It is private to the app Signup and view all the answers

What is a characteristic of external storage?

It can be much larger than internal storage Signup and view all the answers

What happens to the external storage when the app is uninstalled?

It is only wiped in certain cases Signup and view all the answers

What is required to read/write to the external storage?

A special permission in the AndroidManifest.xml file Signup and view all the answers

What happens when the user installs an app that requires external storage permission?

The user is prompted to confirm the app permissions Signup and view all the answers

Study Notes

Android Storage

Android can read and write files from two locations: internal and external storage.
Both are persistent storage, meaning data remains after power-off or reboot.

Internal Storage

Built into the device, guaranteed to be present.
Typically smaller (~1-4 GB).
Can't be expanded or removed.
Specific and private to each app.
Wiped out when the app is uninstalled.

Java File and Streams

java.io.File: represents a file or directory.
Methods: canRead, canWrite, create, delete, exists, getName, getParent, getPath, isFile, isDirectory, lastModified, length, listFiles, mkdir, mkdirs, renameTo.
java.io.InputStream and OutputStream: represent flows of data bytes from/to a source or destination.
Can come from a file, network, database, memory, etc.
Normally not directly used; instead, passed as a parameter to other objects.

Using Internal Storage

An activity has methods to read/write files:
- getFilesDir(): returns internal directory for the app.
- getCacheDir(): returns a "temp" directory for scrap files.
- getResources().openRawResource(R.raw.id): reads an input file from res/raw/.
- openFileInput("name", mode): opens a file for reading.
- openFileOutput("name", mode): opens a file for writing.

External Storage

A card inserted into the device (e.g., MicroSD card).
Can be much larger than internal storage (~8-32 GB).
Can be removed or transferred to another device if needed.
May not be present, depending on the device.
Read/writable by other apps and users; not private to the app.
Not wiped when the app is uninstalled, except in certain cases.

External Storage Permission

Must explicitly request permission in the app's AndroidManifest.xml file.
User will be prompted to confirm app permissions on install.

Using External Storage

Methods to read/write external storage:
- getExternalFilesDir("name"): returns "private" external directory for the app with the given name.
- Environment.getExternalStoragePublicDirectory(name): returns public directory for common files like photos, music, etc.
Pass constants for name, such as Environment.DIRECTORY_ALARMS, DIRECTORY_DCIM, etc.

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