Simplifying Conditional Expression and Making

Method Calls Simpler

Chris Chen

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Outline - Simplifying Conditional Expression

• 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

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Outline - Making Method Calls Simpler

• Rename Method

• Add Parameter

• Remove Parameter

• Separate Query from Modifier

• Parameterize Method

• Replace Parameterize with Explicit

Methods

• Preserve Whole Object

• Replace Parameter with Method

• Introduce Parameter Object

• Remove Setting Method

• Hide Method

• Replace Constructor with Factory

Method

• Encapsulate Downcase

• Replace Error Code with Exception

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SIMPLIFYING CONDITIONAL EXPRESSION

CH10CH9

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Decompose Conditional

• You have a complicated conditional (if-then-else) statement.

• Extract methods from the condition, then part, and else parts.

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After

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Consolidate Conditional Expression - Ors

• You have a sequence of conditional tests with the same result.

• Combine them into a single conditional expression and extract it.

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After

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Consolidate Conditional Expression - Ands

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Consolidate Duplicate Conditional Fragments

• The same fragment of code is in all branches of a conditional expression.

• Move it outside of the expression.

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Remove Control Flag - break

• You have a variable that is acting as a control flag for a series of boolean expressions.

• Use a break or return instead

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Remove Control Flag - return

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Replace Nested Conditional with Guard Clauses

• A method has conditional behavior that does not make clear the normal path of

execution.

• Use guard clauses for all the special cases.

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Replace Nested Conditional with Guard Clauses - Reversing the Conditions

Conditional

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Replace Conditional with Polymorphism

• You have a conditional that chooses different behavior depending on the type of

an object.

• Move each leg of the conditional to an overriding method in a subclass. Make the

original method abstract.

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Replace Conditional with Polymorphism

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Replace Conditional with Polymorphism

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Introduce Null Object

• You have repeated checks for a null value.

• Replace the null value with a null object

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Introduce Null Object

Before

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Introduce Null Object

Step1 Create Null

Customer Class

If you aren't able to modify the Customer

class you can use a testing interface.

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Introduce Null Object

Step 2 Create a Factory

Method and force replace

Null Object with null case

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Introduce Null Object

Step 3 move default case

into Null Object

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MAKING METHOD CALLS SIMPLER

CH10CH9

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Rename Method

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After

• The name of a method does not reveal its purpose.

• Change the name of the method.

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Add Parameter

• A method needs more information from its caller

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Remove Parameter

• A parameter is no longer used by the method body.

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Separate Query from Modifier

• You have a method that returns a value but also changes the state of an object.

• Create two methods, one for the query and one for the modification.

There is a simple example in the book P226

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Parameterize Method

• Several methods do similar things but with different values contained in the method

body.

• Create one method that uses a parameter for the different values.

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Parameterize Method

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Replace Parameterize with Explicit Methods

• You have a method that runs different code depending on the values of an enumerated parameter.

• Create a separate method for each value of the parameter

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Preserve Whole Object

• You are getting several values from an object and passing these values as parameters in a method call.

• Send the whole object instead.

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Replace Parameter with Method

• An object invokes a method, then passes the result as a parameter for a method.

• The receiver can also invoke this method. Remove the parameter and let the receiver invoke the method

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Replace Parameter with Method

Step1 Extract a

method

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Replace Parameter with Method

Step 2 Remove

Parameter and temp

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Replace Parameter with Method

Step 3 create basic

price method and refine

get price method

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Introduce Parameter Object

• You have a group of parameters that naturally go together.

• Replace them with an object

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Introduce Parameter Object

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Introduce Parameter Object

Step1 Create

DateRange Object and

put start-date, end-date

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Introduce Parameter Object

Step2 replace original

param with DateRange

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Introduce Parameter Object

Step3 add one method

includes in DateRange

class

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Remove Setting Method

• You have a group of parameters that naturally go together.

• Replace them with an object

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Remove Setting Method

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Remove Setting Method

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Hide Method

• A method is not used by any other class.

• Make the method private.

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Replace Constructor with Factory Method

• You want to do more than simple construction when you create an object.

• Replace the constructor with a factory method

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Encapsulate Downcase

• A method returns an object that needs to be downcasted by its callers.

• Move the downcast to within the method.

• These case often appear with methods that return collection or iterator

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Replace Error Code with Exception

• A method returns a special code to indicate an error.

• Throw an exception instead.

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Thanks