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Replace Parameter with Explicit Methods.

Problem

A method is split into parts, each of which is run depending on the value of a parameter.

Solution

Extract the individual parts of the method into their own methods and call them instead of the original method.

##Example

Before
void setValue(String name, int value) {
  if (name.equals("height")) {
    height = value;
    return;
  }
  if (name.equals("width")) {
    width = value;
    return;
  }
  Assert.shouldNeverReachHere();
}
After
void setHeight(int arg) {
  height = arg;
}
void setWidth(int arg) {
  width = arg;
}

##Why Refactor

A method containing parameter-dependent variants has grown massive. Non-trivial code is run in each branch and new variants are added very rarely.

##Benefits

  • Improves code readability. It’s much easier to understand the purpose of startEngine() than setValue("engineEnabled", true).

##How to Refactor

  1. For each variant of the method, create a separate method. Run these methods based on the value of a parameter in the main method.

  2. Find all places where the original method is called. In these places, place a call for one of the new parameter-dependent variants.

  3. When no calls to the original method remain, delete it.

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