---
title: "Make things easier on Android with “let” and “apply”"
description: "“let” and “apply” are very useful functions in Kotlin. It could change the way you write your code from what you did in Java"
canonical: https://oozou.com/blog/make-things-easier-on-android-with-let-and-apply-12
locale: en
date: 2017-07-21
author: "OOZOU Team"
---

# Make things easier on Android with “let” and “apply”

> “let” and “apply” are very useful functions in Kotlin. It could change the way you write your code from what you did in Java

Published: 2017-07-21 · Author: OOZOU Team (Engineering) · 3 min read

**“let”** and “**apply”** are very useful functions in Kotlin. It could change the way you write your code from what you did in Java. In this article, I would like to share how to make your code easier with **“let”** and **“apply”.** I will assume that you have some basic knowledge about Kotlin.

# What can “**let”** do?

I would like to point out two main usages of **“let”**

1. **Scoping Function: “let”** could be used to make your code self-contain in the “**let”** block and keep the logic separate. The variable in front of **“let”** could be referred to as **it.** Look at the code below as an example.

```kotlin
File("dummy.txt").let {
  print(it.toString())
}
//File "dummy.txt" is not visible here
```

As you can see that the **File(“dummy.txt”)** will only be visible in the **“let”** block.
2. **Check against null:** In Java, to prevent our lovely **NullPointerException** we have to repeatedly check for **null** in our code. Fortunately, we could make things easier with “**let”.** We can make the “**let”** block execute only when the variable is not **null**. Let’s see an example.

Suppose we have an object like this
**user** \-(hold)-> **info** \-(hold)-> **email**Both **user** and **info** could be **null.** This is how we would do this in Java.

```kotlin
if(user != null) {
  Info info = user.getInfo();
  if (info != null) {
    String email = info.getEmail();
    if(email != null) {
        sendEmailToUser(email)
    }
  }
}
```

And in Kotlin :)

```kotlin
user?.info?.email?.let? {
    sendEmailToUser(it)
}
```

As you can see that it’s much shorter and cleaner in Kotlin.

# ow to use “apply”?

**“apply”** may help you write the code in a slightly different way

**“apply”** can be used as an extension of all types of variables. It will **return** the object with the thing in the “**apply”** block apply to the object (it works according to its name). Let’s see things in action to get a clearer picture.

Here are a couple of examples:

1. In Java, when we try to set up **RecyclerView**. We might do something like this.

```kotlin
recyclerView.setLayoutManager(new LinearLayoutManager(this));
recyclerView.setAdapter(new YourRecyclerViewAdapter(this));
recyclerView.setHasFixedSize(true)
```

With **“apply”** in Kotlin, we could make it this way.

```kotlin
recyclerView.apply {
  layoutManager = LinearLayoutManager(this@YourActivity)
  setHasFixedSize(true)
  adapter = YourRecyclerViewAdapter(this@YourActivity)
}
```

2. Creating an object through setter in Java might require something like

```kotlin
User user = new User();
user.setFirstName = "John";
user.setLastName = "Doe";
user.setGender = "Male";
user.setProfileUrl = "...";
user.setPhoneNumber = "...";
```

With **“apply”** we could make things slightly better

```kotlin
User user = User().apply {
  firstName = "John"
  lastName = "Doe"
  gender = "male"
  profileUrl = "..."
  phoneNumber = "..."
}
```

Inside **“apply”** block we can refer to “properties” or “methods” of the variable that used **“apply”** without having to refer to that variable again.

# Conclusion
In my opinion **“let”** does make the code shorter and cleaner, especially the ability to **check against null.** Since as an Android developer we all might have to write many lines of code to check for **null** values in Java to prevent **NullPointerException** and **“let”** does solve that pain. For **“apply”,** I think it helps to avoid repeatedly referencing the same variable and makes the code a bit easier to read.

# Reference

[http://beust.com/weblog/2015/10/30/exploring-the-kotlin-standard-library/](http://beust.com/weblog/2015/10/30/exploring-the-kotlin-standard-library/)

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