Extract Method

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Extracting a method consists of turning a fragment of a method into a method whose name explains the purpose of the method. This may need to be used in methods that show a large number of local variables within the scope of a method, to enhance comprehensibility and reduce complexity. If several of these local-scope variables are modified by the code extracted, Split Temporary Variable may also need to be used.

In cases where extracting a method is not feasible, replacing the method with a Method Object may be the next step.


Example:

printOwing() {
               printBanner();
       
               //print details
               System.out.println ("name:	" + _name);
               System.out.println ("amount	" + getOutstanding());
       }

becomes

       void printOwing() {
               printBanner();
               printDetails(getOutstanding());
       }

       void printDetails (double outstanding) {
               System.out.println ("name:	" + _name);
               System.out.println ("amount	" + outstanding);
       }

See Also


Refactoring

Composing Methods: Extract Method | Inline Method | Inline Temp | Replace Temp with Query | Introduce Explaining Variable | Split Temporary Variable | Remove assignments to Parameters | Replace Method with Method Object | Substitute Algorithm
Moving Features Between Objects: Move Method | Move Field | Extract Class | Inline Class | Hide Delegate | Remove Middle Man | Introduce Foreign Method | Introduce Local Extension
Organising Data: Self Encapsulate Field | Replace Data Value with Object | Change Value to Reference | Change Reference to Value | Replace Array with Object | Duplicate Observed Data | Change Unidirectional Association to Bidirectional | Change Bidirectional Association to Unidirectional | Replace Magic Number with Symbolic Constant | Encapsulate Field | Encapsulate Collection | Replace Type Code with Class | Replace Type Code with Subclass | Replace Type Code with State/Strategy
Simplifying Conditional Expressions: Decompose Conditional | Consolidate Conditional Expression | Consolidate Duplicate Conditional Fragments | Remove Control Flag | Replace Nested Conditional with Guard Clauses | Replace Conditional with Polymorphism | Introduce Null Object | Introduce Assertion
Making Method Calls Simpler: Rename Method | Add Parameter | Remove Parameter | Separate Query from Modifier | Parameterise Method | Replace Parameter with Explicit Methods | Preserve Whole Object | Replace Parameter with Method | Introduce Parameter Object | Replace Parameter Object | Remove Setting Method | Hide Method | Replace Constructor with Factory Method | Encapsulate Downcast | Replace Error Code with Exception | Replace Exception with test
Dealing with Generalisation: Pull Up Field | Pull Up Method | Pull Up Constructor Body | Push Down Field | Push Down Method | Extract Subclass | Extract Superclass | Extract Interface | Collapse Hierarchy | Form Template Method | Replace Inheritance with Delegation
Big Refactorings: Tease Apart Inheritance | Convert Procedural Design to Objects | Separate Domain from Presentation | Extract Hierarchy

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