File access and storage in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to open a file for writing in internal storage.

Android Kotlin

val fileOutput = openFileOutput("myfile.txt", [1])

Drag options to blanks, or click blank then click option'

AContext.MODE_WORLD_READABLE

BContext.MODE_APPEND

CContext.MODE_MULTI_PROCESS

DContext.MODE_PRIVATE

Attempts:

3 left

💡 Hint

Common Mistakes

Using append mode when you want to overwrite

Using deprecated or insecure modes

Use Context.MODE_PRIVATE to create or open a file that is private to your app.

2fill in blank

medium

Complete the code to read text from a file in internal storage.

Android Kotlin

val inputStream = openFileInput("myfile.txt")
val text = inputStream.bufferedReader().use { it.[1]() }

Drag options to blanks, or click blank then click option'

AreadLines

BreadText

CreadBytes

DreadChars

Attempts:

3 left

💡 Hint

Common Mistakes

Using readLines() which returns a list of strings

Using readBytes() which returns bytes, not string

readText() reads the entire content of the file as a single string.

3fill in blank

hard

Fix the error in the code to write a string to a file safely.

Android Kotlin

val fileOutput = openFileOutput("data.txt", Context.MODE_PRIVATE)
fileOutput.[1]("Hello World".toByteArray())
fileOutput.close()

Drag options to blanks, or click blank then click option'

Aclose

Bflush

Cwrite

Dread

Attempts:

3 left

💡 Hint

Common Mistakes

Using flush() instead of write()

Trying to read from output stream

Use write() to write bytes to the file output stream.

4fill in blank

hard

Fill both blanks to check if a file exists and delete it.

Android Kotlin

val file = File(filesDir, "temp.txt")
if (file.[1]()) {
  file.[2]()
}

Drag options to blanks, or click blank then click option'

Aexists

Bdelete

CcreateNewFile

DisFile

Attempts:

3 left

💡 Hint

Common Mistakes

Using createNewFile() instead of delete()

Checking isFile() which only checks type, not existence

Use exists() to check if the file is there, and delete() to remove it.

5fill in blank

hard

Fill all three blanks to write and then read a string from a file.

Android Kotlin

val filename = "log.txt"
val output = openFileOutput(filename, [1])
output.write("Test Entry".toByteArray())
output.close()

val input = openFileInput(filename)
val content = input.bufferedReader().[2] { it.[3]() }

Drag options to blanks, or click blank then click option'

AContext.MODE_PRIVATE

BreadText

Cuse

DContext.MODE_APPEND

Attempts:

3 left

💡 Hint

Common Mistakes

Using append mode when overwriting is intended

Not closing streams properly

Using readLines() instead of readText()

Use Context.MODE_PRIVATE to open the file for writing, then use to safely handle the reader, and readText() to get the file content as a string.

Practice

1. Which method is used in Android Kotlin to write data to a private file within the app's internal storage?

easy

A. writeExternalStorage

B. openFileInput

C. readFile

D. openFileOutput

Solution

1. Step 1: Understand file writing methods

   openFileOutput is the method designed to write data to a private file in internal storage.

2. Step 2: Differentiate from reading methods

   openFileInput is used for reading, not writing files.

3. Final Answer:

   openFileOutput -> Option D

4. Quick Check:

   Write file = openFileOutput [OK]

Hint: Writing files uses openFileOutput, reading uses openFileInput [OK]

Common Mistakes:

• Confusing openFileInput with writing method
• Using external storage methods for internal files
• Assuming readFile is a valid Android method

2. Which of the following is the correct Kotlin syntax to open a file named "data.txt" for reading in an Android app?

easy

A. val input = openFileOutput("data.txt", Context.MODE_PRIVATE)

B. val input = openFileInput("data.txt")

C. val input = openFile("data.txt", Context.MODE_PRIVATE)

D. val input = readFile("data.txt")

Solution

1. Step 1: Identify the correct method for reading files

   openFileInput is the correct method to open a file for reading in Android Kotlin.

2. Step 2: Check syntax correctness

   openFileInput takes only the filename as a parameter, no mode needed.

3. Final Answer:

   val input = openFileInput("data.txt") -> Option B

4. Quick Check:

   Read file = openFileInput(filename) [OK]

Hint: openFileInput(filename) opens file for reading [OK]

Common Mistakes:

• Using openFileOutput for reading
• Adding mode parameter to openFileInput
• Using non-existent readFile method

3. What will be the output of the following Kotlin code snippet in an Android app?

val filename = "note.txt"
val fileContents = "Hello World"
openFileOutput(filename, Context.MODE_PRIVATE).use {
  it.write(fileContents.toByteArray())
}
val input = openFileInput(filename).bufferedReader().use { it.readText() }
println(input)

medium

A. note.txt

B. null

C. Hello World

D. FileNotFoundException

Solution

1. Step 1: Write text to file

   The code writes "Hello World" to "note.txt" using openFileOutput.

2. Step 2: Read text from the same file

   openFileInput reads the file content back as a string.

3. Final Answer:

   Hello World -> Option C

4. Quick Check:

   Write then read file = "Hello World" [OK]

Hint: Write then read file returns the original string [OK]

Common Mistakes:

• Expecting filename instead of content
• Assuming file is empty or null
• Not closing streams causing errors

4. Consider this Kotlin code snippet in an Android app:

val input = openFileInput("config.txt")
val text = input.bufferedReader().readText()
input.close()

What is the main issue with this code?

medium

A. Not using 'use' block to safely close the stream

B. The input stream is closed before reading text

C. bufferedReader() cannot be called on input streams

D. openFileInput should be called with Context.MODE_PRIVATE

Solution

1. Step 1: Check resource management

   The code manually closes the input stream but risks exceptions if readText() fails.

2. Step 2: Use 'use' block for safety

   Using 'use' automatically closes the stream safely even if errors occur.

3. Final Answer:

   Not using 'use' block to safely close the stream -> Option A

4. Quick Check:

   Safe stream closing = use block [OK]

Hint: Always use 'use' to auto-close streams safely [OK]

Common Mistakes:

• Adding mode parameter to openFileInput
• Closing stream before reading
• Believing bufferedReader() is invalid here

5. You want to save user preferences as a JSON string in a private file named "prefs.json" and then read it back safely. Which Kotlin code snippet correctly writes and reads this file in an Android app?

hard

A. openFileOutput("prefs.json", Context.MODE_PRIVATE).use { it.write(jsonString.toByteArray()) }
val json = openFileInput("prefs.json").bufferedReader().use { it.readText() }

B. openFileInput("prefs.json").use { it.write(jsonString.toByteArray()) }
val json = openFileOutput("prefs.json", Context.MODE_PRIVATE).bufferedReader().use { it.readText() }

C. val file = File("prefs.json")
file.writeText(jsonString)
val json = file.readText()

D. val fos = openFileOutput("prefs.json")
fos.write(jsonString.toByteArray())
fos.close()
val fis = openFileInput("prefs.json")
val json = fis.bufferedReader().readText()
fis.close()

Solution

1. Step 1: Write file using openFileOutput with 'use'

   openFileOutput("prefs.json", Context.MODE_PRIVATE).use { it.write(jsonString.toByteArray()) } val json = openFileInput("prefs.json").bufferedReader().use { it.readText() } correctly writes the JSON string to "prefs.json" using openFileOutput and safely closes the stream with 'use'.

2. Step 2: Read file using openFileInput with 'use'

   It then reads the file back safely using openFileInput and 'use' to auto-close the stream.

3. Final Answer:

   openFileOutput("prefs.json", Context.MODE_PRIVATE).use { it.write(jsonString.toByteArray()) } val json = openFileInput("prefs.json").bufferedReader().use { it.readText() } -> Option A

4. Quick Check:

   Write/read private file safely = openFileOutput/input + use [OK]

Hint: Use openFileOutput/input with 'use' to safely write/read files [OK]

Common Mistakes:

• Mixing up openFileInput and openFileOutput
• Using File class for internal storage without context
• Not closing streams properly causing leaks