---
title: "Extract Variable"
type: "refactoring-technique"
slug: "extract-variable"
url: "http://localhost:3000/en/extract-variable.md"
category: "Composing Methods"
description: "Problem: You have an expression that’s hard to understand. Solution: Place the result of the expression or its parts in separate variables that are self-explanatory."
languages: ["java", "csharp", "php", "python", "typescript"]
---
# Extract Variable

> Problem: You have an expression that’s hard to understand. Solution: Place the result of the expression or its parts in separate variables that are self-explanatory.

## Problem

You have an expression that’s hard to understand.

## Solution

Place the result of the expression or its parts in separate variables that are self-explanatory.

## Why Refactor

The main reason for extracting variables is to make a complex expression more understandable, by dividing it into its intermediate parts. These could be:

* Condition of the `if()` operator or a part of the `?:` operator in C-based languages
* A long arithmetic expression without intermediate results
* Long multipart lines

Extracting a variable may be the first step towards performing [Extract Method](/extract-method) if you see that the extracted expression is used in other places in your code.

## Benefits

* More readable code! Try to give the extracted variables good names that announce the variable’s purpose loud and clear. More readability, fewer long-winded comments. Go for names like `customerTaxValue`, `cityUnemploymentRate`, `clientSalutationString`, etc.

## How to Refactor

1. Insert a new line before the relevant expression and declare a new variable there. Assign part of the complex expression to this variable.
2. Replace that part of the expression with the new variable.
3. Repeat the process for all complex parts of the expression.
## Relations

**Similar techniques**

- [Extract Method](/en/extract-method.md)

**Opposite refactorings**

- [Inline Temp](/en/inline-temp.md)

**Eliminates smells**

- [Comments](/en/smells/comments.md)

## Code Examples

### java

```java
// Before
void renderBanner() {
  if ((platform.toUpperCase().indexOf("MAC") > -1) &&
       (browser.toUpperCase().indexOf("IE") > -1) &&
        wasInitialized() && resize > 0 )
  {
    // do something
  }
}

// After
void renderBanner() {
  final boolean isMacOs = platform.toUpperCase().indexOf("MAC") > -1;
  final boolean isIE = browser.toUpperCase().indexOf("IE") > -1;
  final boolean wasResized = resize > 0;

  if (isMacOs && isIE && wasInitialized() && wasResized) {
    // do something
  }
}
```

### csharp

```csharp
// Before
void RenderBanner() 
{
  if ((platform.ToUpper().IndexOf("MAC") > -1) &&
       (browser.ToUpper().IndexOf("IE") > -1) &&
        wasInitialized() && resize > 0 )
  {
    // do something
  }
}

// After
void RenderBanner() 
{
  readonly bool isMacOs = platform.ToUpper().IndexOf("MAC") > -1;
  readonly bool isIE = browser.ToUpper().IndexOf("IE") > -1;
  readonly bool wasResized = resize > 0;

  if (isMacOs && isIE && wasInitialized() && wasResized) 
  {
    // do something
  }
}
```

### php

```php
// Before
if (($platform->toUpperCase()->indexOf("MAC") > -1) &&
     ($browser->toUpperCase()->indexOf("IE") > -1) &&
      $this->wasInitialized() && $this->resize > 0)
{
  // do something
}

// After
$isMacOs = $platform->toUpperCase()->indexOf("MAC") > -1;
$isIE = $browser->toUpperCase()->indexOf("IE")  > -1;
$wasResized = $this->resize > 0;

if ($isMacOs && $isIE && $this->wasInitialized() && $wasResized) {
  // do something
}
```

### python

```python
// Before
def renderBanner(self):
    if (self.platform.toUpperCase().indexOf("MAC") > -1) and \
       (self.browser.toUpperCase().indexOf("IE") > -1) and \
       self.wasInitialized() and (self.resize > 0):
        # do something

// After
def renderBanner(self):
    isMacOs = self.platform.toUpperCase().indexOf("MAC") > -1
    isIE = self.browser.toUpperCase().indexOf("IE") > -1
    wasResized = self.resize > 0

    if isMacOs and isIE and self.wasInitialized() and wasResized:
        # do something
```

### typescript

```typescript
// Before
renderBanner(): void {
  if ((platform.toUpperCase().indexOf("MAC") > -1) &&
       (browser.toUpperCase().indexOf("IE") > -1) &&
        wasInitialized() && resize > 0 )
  {
    // do something
  }
}

// After
renderBanner(): void {
  const isMacOs = platform.toUpperCase().indexOf("MAC") > -1;
  const isIE = browser.toUpperCase().indexOf("IE") > -1;
  const wasResized = resize > 0;

  if (isMacOs && isIE && wasInitialized() && wasResized) {
    // do something
  }
}
```