Copyright 2009 Trend Micro Inc.

New Hires Orientation

Refactoring Ch8 (part 1)Mel Huang

Copyright 2009 Trend Micro Inc.

Outline

• 8.1 Self Encapsulate Field

• 8.2 Replace Data Value with Object

• 8.3 Change Value to Reference

• 8.4 Change Reference to Value

• 8.5 Replace Array with Object

• 8.6 Duplicate Observed Data

• 8.7 Change Unidirectional Association to Bidirectional

• 8.8 Change Bidirectional Association to Unidirectional

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Copyright 2009 Trend Micro Inc.

8.1 Self Encapsulate Field

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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() { return _high; }int setLow(int low) { _low = low; }int setHigh(int high) { _high = high; }

direct access: simple!

getter/setter: flexible!

Copyright 2009 Trend Micro Inc.

8.2 Replace Data Value with Object

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class Order { public Order (String customer) { _customer = customer; } private String _customer;}

class Customer { public Customer (String name) { _name = name; } public String getName() { return _name; } private final String _name;}

class Order { public Order (String customer) { _customer = new Customer(customer); } private Customer _customer;}

data value object: easier to complicate data

item(s)

Copyright 2009 Trend Micro Inc.

8.3 Change Value to Reference

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class Customer { public Customer (String name) { _name = name; } public String getName() { return _name; } private final String _name;}

class Order { public Order (String customer) { _customer = new Customer(customer); } private Customer _customer;}

class Customer { public static Customer create (String name) { return (Customer) _instances.get(name); } static void loadCustomers() { new Customer("Lemon Car Hire").store(); new Customer("Associated Coffee Machines").store(); ... } private void store() { _instances.put(this.getName(), this); } public String getNamed(String name) { return (Customer) _instances.get(name); } private final String _name; private static Dictionary _instances = new Hashtable();}

class Order { public Order (String customer) { _customer = Customer.create(customer); } private Customer _customer;}

Order Customer

Order Customer

…

Order

Order Customer

…

*

*

Copyright 2009 Trend Micro Inc.

8.4 Change Reference to Value

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class Currency { private String _code;

public String getCode() { return _code; } private Currency (String code) { _code = code; }}

class Currency { private String _code;

public String getCode() { return _code; } private Currency (String code) { _code = code; } public boolean equals(Object arg) { if (! (arg instanceof Currency)) return false; Currency other = (Currency) arg; return (_code.equals(other._code)); } public int hashCode() { return _code.hashCode(); }}

immutable?

Copyright 2009 Trend Micro Inc.

8.5 Replace Array with Object

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String[] row = new String[3];row[0] = "Liverpool";row[1] = "15";

Performance row = new Performance();row.setName("Liverpool");row.setWins("15");

array: hard to remember each column

object: easy to maintain

Copyright 2009 Trend Micro Inc.

8.6 Duplicate Observed Data

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public class IntervalWindow extends Frame { TextField _startField; TextField _endField; TextField _lengthField;

void StartField_FocusLost(FocusEvent event) { ... calculateLength(); } void EndtField_FocusLost(FocusEvent event) { ... calculateLength(); } void StartField_FocusLost(FocusEvent event) { ... calculateLength(); }

void calculateLength() { ... } void calculateEnd() { ... }}

public class IntervalWindow extends Frame implements Observer { private Interval _subject; TextField _startField; TextField _endField; TextField _lengthField;

public IntervalWindow() { _subject = new Interval(); _subject.addObserver(this); update(_subject, null); } public void update(Observable observed, Object arg) { _endField.setText(_subject.getEnd()); } String getEnd() { return _subject.getEnd(); } void setEnd (Srting arg) { _subject.setEnd(arg); } void StartField_FocusLost(FocusEvent event) { ... calculateLength(); } void EndtField_FocusLost(FocusEvent event) { ... calculateLength(); } void StartField_FocusLost(FocusEvent event) { ... calculateLength(); }}

class Interval extends Observable { void calculateLength() { ... } void calculateEnd() { ... }}

Copyright 2009 Trend Micro Inc.

8.7 Change Unidirectional Association to Bidirectional

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class Order { Customer getCustomer() { return _customer; } void setCustomer (Customer arg) { _customer = arg; } Customer _customer; // order->customer}

class Customer { private Set _orders = new HashSet();}

class Order { Customer getCustomer() { return _customer; } void setCustomer (Customer arg) { if (_customer != null) _customer.friendOrders().remove(this); _customer = arg; if (_customer != null) _customer.friendOrders().add(this); } Customer _customer; // order->customer}

class Customer { private Set _orders = new HashSet(); Set friendOrders() { return _orders } void addOrder(Order arg) { arg.setCustomer(this); }}

Order Customer*Order Customer*

Copyright 2009 Trend Micro Inc.

8.8 Change Bidirectional Association to Unidirectional

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Order Customer*Order Customer*

class Order { Customer getCustomer() { return _customer; } void setCustomer (Customer arg) { if (_customer != null) _customer.friendOrders().remove(this); _customer = arg; if (_customer != null) _customer.friendOrders().add(this); } double getDiscountedPrice() { return getGrossPrice() * (1 - _customer.getDiscount()); } Customer _customer; // order->customer}

class Customer { getPriceFor(Order order) { Assert.isTrue(_orders.contains(order)); return order.getDiscountedPrice(); }}

class Order { Customer getCustomer() { return _customer; } Customer setCustomer () { Iterator iter = Customer.getInstances().iterator(); while (iter.hasNext()) { Customer each = (Customer)iter.next(); if (each.containsOrder(this)) return each; } return null; } double getDiscountedPrice(Customer customer) { return getGrossPrice() * (1 - customer.getDiscount()); } Customer _customer; // order->customer}

class Customer { getPriceFor(Order order) { Assert.isTrue(_orders.contains(order)); return order.getDiscountedPrice(this); }}

Copyright 2009 Trend Micro Inc.

Thank You

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