---
title: "Decompose Conditional"
type: "refactoring-technique"
slug: "decompose-conditional"
url: "http://localhost:3000/en/decompose-conditional.md"
category: "Simplifying Conditional Expressions"
description: "Problem: You have a complex conditional (if-then/else or switch). Solution: Decompose the complicated parts of the conditional into separate methods: the condition, then and else."
languages: ["java", "csharp", "php", "python", "typescript"]
---
# Decompose Conditional

> Problem: You have a complex conditional (if-then/else or switch). Solution: Decompose the complicated parts of the conditional into separate methods: the condition, then and else.

## Problem

You have a complex conditional (`if-then`/`else` or `switch`).

## Solution

Decompose the complicated parts of the conditional into separate methods: the condition, `then` and `else`.

## Why Refactor

The longer a piece of code is, the harder it’s to understand. Things become even more hard to understand when the code is filled with conditions:

* While you’re busy figuring out what the code in the `then` block does, you forget what the relevant condition was.
* While you’re busy parsing `else`, you forget what the code in `then` does.

## Benefits

* By extracting conditional code to clearly named methods, you make life easier for the person who’ll be maintaining the code later (such as you, two months from now!).
* This refactoring technique is also applicable for short expressions in conditions. The string `isSalaryDay()` is much prettier and more descriptive than code for comparing dates.

## How to Refactor

1. Extract the conditional to a separate method via [Extract Method](/extract-method).
2. Repeat the process for the `then` and `else` blocks.
## Relations

**Eliminates smells**

- [Long Method](/en/smells/long-method.md)

## Code Examples

### java

```java
// Before
if (date.before(SUMMER_START) || date.after(SUMMER_END)) {
  charge = quantity * winterRate + winterServiceCharge;
}
else {
  charge = quantity * summerRate;
}

// After
if (isSummer(date)) {
  charge = summerCharge(quantity);
}
else {
  charge = winterCharge(quantity);
}
```

### csharp

```csharp
// Before
if (date < SUMMER_START || date > SUMMER_END) 
{
  charge = quantity * winterRate + winterServiceCharge;
}
else 
{
  charge = quantity * summerRate;
}

// After
if (isSummer(date))
{
  charge = SummerCharge(quantity);
}
else 
{
  charge = WinterCharge(quantity);
}
```

### php

```php
// Before
if ($date->before(SUMMER_START) || $date->after(SUMMER_END)) {
  $charge = $quantity * $winterRate + $winterServiceCharge;
} else {
  $charge = $quantity * $summerRate;
}

// After
if (isSummer($date)) {
  $charge = summerCharge($quantity);
} else {
  $charge = winterCharge($quantity);
}
```

### python

```python
// Before
if date.before(SUMMER_START) or date.after(SUMMER_END):
    charge = quantity * winterRate + winterServiceCharge
else:
    charge = quantity * summerRate

// After
if isSummer(date):
    charge = summerCharge(quantity)
else:
    charge = winterCharge(quantity)
```

### typescript

```typescript
// Before
if (date.before(SUMMER_START) || date.after(SUMMER_END)) {
  charge = quantity * winterRate + winterServiceCharge;
}
else {
  charge = quantity * summerRate;
}

// After
if (isSummer(date)) {
  charge = summerCharge(quantity);
}
else {
  charge = winterCharge(quantity);
}
```