Composing Methods. Extract Method - Code that can be grouped - Meaningful name for method

Transcription

1 Composing Methods Extract Method - Code that can be grouped - Meaningful name for method Inline Method - inverse of Extract Method - Method body is more obvious Extract Variable - Expression: hard to understand - Separate self-explanatory var Inline Temp Replace Temp with Query - Temp var holding expression - Extract Expression into method Split Temporary Variable - different var for different value void printowing(double amount){ //print details System.out.println( name: +name); System.out.println( amount: + amount); void printowing(double mount){ printdetails(name, amount); void printdetails(string name, double amount){ System.out.println( name: +name); System.out.println( amount: + amount); int getrating() { return (morethanfivelatedeliveries()?2:1; Boolean morethanfivelatedeliveries() { return numberoflatedeliveries > 5; int getrating() { return (numberoflatedeliveries >5)?2:1; if((platform.touppercase().indexof( MAC ) > -1) && (browser.touppercase().indexof( IE ) > -1) && wasinitialized() && resize > 0) { //do something final boolean ismacos = platform.touppercase().indexof( MAC ) > -1; final boolean isiebrowser = browser.touppercase().indexof( IE ) > -1; final Boolean wasresized = resize > 0; if (ismacos && isiebrowser && wasinitialized() && wasresized) { //do something double baseprice = anorder.baseprice(); return (baseprice > 1000); return (anorder.baseprice() > 1000); double baseprice = quantity * itemprice; if (baseprice > 1000) return baseprice * 0.95; else return baseprice; if (baseprice() > 1000) return baseprice() * 0.95; else return baseprice() * 0.98; double baseprice() { return quantity * itemprice; double temp = 2 * (height + width); System.out.println(temp); temp = height * width; System.out.println(temp); 1 11

2 Composing Methods Remove Assignments to Param - use temp var instead Replace Method with Method Obj - Extract Method cannot be applied - Separate class Substitute Algorithm - Replace existing algorithm - Replace body of the method final double perimeter = 2 * (height + width); System.out.println(perimeter); final double area = height * width; System.out.println(area); int discount(int inputval, int Quantity, int yeartodate){ if (intputval>50) inputval -=2; int discount(int inputval, int Quantity, int yeartodate) { int result = inputval; if (inputval > 50) result - = 2; class Order { double price() { double primarybaseprice; double secondarybaseprice; double TeriaryBasePrice; //long computation class Order { public double price() { return new PriceCalculator(this).compute(); class PriceCalculator { private double primarybaseprice; private double seconadarybaseprice; private double tertiarybaseprice; PriceCalculator(Order order) { //copy relevant info public double compute() { // String foundperson(string[] people) { for(int I = 0;i<people.length;i++) { if(people[i].equals( Don )) return Don ; if((people[i].equals( John )) return John ; if(people[i].equals( Kent )) return Kent ; return ; 2 11

3 Composing Methods Moving Feature btwn Obj Move Method - Use more features in another class Move Field - Field used by another class more String foundperson(string[] people) { ListCandidates = Arrays.asList(new String[] { Don, John, Kent ); for(int i = 0;i<people.length;;i++) { if (candidates.contains(people[i])) { return people[i]; return ; Extract Class - One class does the work of two Inline Class - Class does almost nothing Hide Delegate - use A for getting B info - new method of A delegating B Remove Middle Man - too many methods that simply delegate - force the client to call the end methods directly Introduce Foreign method - server class cannot contain the needed class - add a method in the client Date newstart = new Date(previousEnd.getYear(), previousend.getmonth(), previousend.getdate() + 1); Date newstart = nextday(previousend); private static Date nextday(date arg) { return new Date(arg.getYear(), arg.getmonth(), arg.getdate() + 1); 3 11

4 Moving Feature btwn Obj Organizing Data Introduce Local Extension - server class cannot contain some methods that you need Self Encapsulate Field - Create a getter and setter Replace Data Value with Object - Contain a data field with its own behavior and associated data - Change the data item into an object Change Value to Reference - Many identical instances of a single class - Converted to a single reference object Change Reference to Value - Reference object is too small - Converted it into a value object Replace Array with Object - Arrays containing various types of data - Replace array with an object Duplicate Observed Data - Domain data in GUI control - Copy data to model and set up observer private int low, high Boolean includes(int arg) { return arg >= low && arg <= high; private int low, high Boolean includes(int arg) { return arg >= getlow() && arg <= gethigh(); int getlow() { return low; int gethigh() { rturn high; String[] row = new String[]; row[0] = Liverpool ; row[1] = 15 ; Performance row = new Performance(); row.setname( Liverpool ); row.setwins( 15 ); Change Unidirectional Association to Bidirectional - Add missing association Change Bidirectional Association to Unidirectional - Remove unused association 4 11

5 Organizing Data Replace Magic Number with Symbolic Constant - number having a certain meaning - Replace with constant double potentialenergy(double mass, double height) { return mass * 9.81 * height; double potentialenergy(double mass, double height) { return mass * GRAVITATION_CONSTANT * height; static final double GRAVITATION_ONSTANT = 9.81; Encapsulate Field - make public field as private - provide accessors Encapsulate Collection - Collection Field with a simple getter/setter - Getter returns read-only, Setter replaced with adding/removing elements Replace Type Code with Class - fields containing type code - Create a new class and use its objects instead (Obsolete: Java enumeration is another option) Replace Type Code with Subclasses - immutable type code affecting the behavior - Create subclasses for each value (OCP) public String name; private String name; public String getname() { return name; public String setname(string arg) { name = arg; Replace Type Code with State/Strategy - Type code affects behavior, but cannot use subclassing - Replace Type code with State/Strategy Replace Subclass with Fields - Subclass differs in constant-returning methods - Remove subclass 5 11

6 Simplifying Conditional Expression Decompose conditional - Complex conditional - Decompose to separate methods if(data.before(summer_start) date.after(summer_end)) charge = quantity * winterrate + winterservicecharge; else charge = quantity * summerrate; if(notsummer(date)) charge = wintercharge(quantity); else charge = summercharge(quantity); Consolidate Conditional Expression double disabilityamount() P if (seniority < 2) if(mounthsdisabled > 12) if (ispattime) double disabilityamount() { if(isnorteligablefordisability()) Consolidate Duplicate Conditional if (isspecialdeal()) { Fragments total = price* 0.95; send(); else { total = price * 0.98; send(); if (isspecialdeal()) { total = price* 0.95; else { total = price * 0.98; send(); Remove Control Flag void checksecurity(string[] people) { boolean found = false; for (int i = 0; i < people.length; i++) { if (! found) { if (people[i].equals ("Don")){ sendalert(); found = true; if (people[i].equals ("John")){ sendalert(); found = true; 6 11

7 Simplifying Conditional Expression Remove Control Flag void checksecurity(string[] people) { boolean found = false; for (int i = 0; i < people.length; i++) { if (people[i].equals ("Don")){ sendalert(); found = true; break; if (people[i].equals ("John")){ sendalert(); found = true; break; Replace Nested Conditional with Guard double getpayamount() { Clauses double result; if (_isdead) result = deadamount(); else { if (_isseparated) result = separatedamount(); else { if (_isretired) result = retiredamount(); else result = normalpayamount(); ; return result; ; double getpayamount() { if (_isdead) return deadamount(); if (_isseparated) return separatedamount(); if (_isretired) return retiredamount(); return normalpayamount(); ; Replace Conditional with Polymorphism Introduce Null Object Introduce Assertion double getexpenselimi() { //should have either expense limit or a primary project return (expenselimit!= NULL_EXPSENSE)? expenselimit ;:primaryproject.getmemberexpenselimit() 7 11

8 Simplifying Conditional Expression Simplifying Method Calls Rename Method double getexpenselimi() { Assert.isTrue(expenseLimit!=NULL_EXPENSE primaryproject!= null); return (expenselimit!= NULL_EXPSENSE)? expenselimit ;:primaryproject.getmemberexpenselimit() Add Parameter Remove Parameter Separate Query from Modifier Parameterize Method Replace Param with Explicit Method void setvalue (String name, int value) { if (name.equals("height")) _height = value; if (name.equals("width")) _width = value; Assert.shouldNeverReachHere(); void setheight(int arg) { _height = arg; void setwidth (int arg) { _width = arg; Preserve Whole Object int low = daystemprange().getlow(); int high = daystemprange().gethigh(); withinplan = plan.withinrange(low, high); withinplan = plan.withinrange(daystemprange()); Replace Parameter with Method Call int baseprice = _quantity * _itemprice; discountlevel = getdiscountlevel(); double finalprice = discountedprice (baseprice, discountlevel); int baseprice = _quantity * _itemprice; double finalprice = discountedprice (baseprice); Introduce Parameter Object 8 11

9 Simplifying Method Calls Remove Setting Method Hide Method Dealing with Generalizatio n Replace Constructor With Factory Employee (int type) { Method _type = type; static Employee create(int type) { return new Employee(type); Encapsulate Downcast Object lastreading() { (Needed?) return readings.lastelement(); Reading lastreading() { return (Reading) readings.lastelement(); Replace Error Code With Exception int withdraw(int amount) { if (amount > _balance) return -1; else { _balance -= amount; void withdraw(int amount) throws BalanceException { if (amount > _balance) throw new BalanceException(); _balance -= amount; Replace Exception With Test double getvalueforperiod (int periodnumber) { try { return _values[periodnumber]; catch (ArrayIndexOutOfBoundsException e) { double getvalueforperiod (int periodnumber) { if (periodnumber >= _values.length) return _values[periodnumber]; Pull Up Field 9 11

10 Dealing with Generalizatio n Pull Up Method Pull Up Constructor Body Push Down Method class Manager extends Employee... public Manager (String name, String id, int grade) { _name = name; _id = id; _grade = grade; public Manager (String name, String id, int grade) { super (name, id); _grade = grade; Push Down Field Extract Subclass Extract Superclass Extract Interface Collapse Hierarchy 10 11

11 Dealing with Generalizatio n From Template Method Replace Inheritance with Delegation Replace Delegation with Inheritance Big Refractorings Tease Apart Inheritance Convert Procedural Design to Objects Separate Domain from Presentation Extract Hierarchy 11 11