设计模式教程（Design Patterns Tutorial）笔记之二 结构型模式（Structural Patterns）

目录

· Decorator

    · What is the Decorator Design Pattern?

    · Sample Code 

· Adapter

    · What is the Adapter Design Pattern?

    · Sample Code

· Facade

    · What is the Facade Design Pattern?

    · Sample Code

· Bridge

    · What is the Bridge Design Pattern?

    · When to use the Bridge Design Pattern?

    · Sample Code

· Flyweight

    · What is the Flyweight Design Pattern?

    · Sample Code

· Proxy

    · What is the Proxy Design Pattern?

    · Sample Code

---

Decorator

What is the Decorator Design Pattern?

• The Decorator allows you to modify an object dynamically.

• You would use it when you want the capabilities of inheritance with subclasses, but you need to add functionality at run time.

• It is more flexible than inheritance.

• Simplifies code because you add functionality using many simple classes.

• Rather than rewrite old code you can extend with new code.

Sample Code 

• Pizza.java 

// Blueprint for classes that will have decorators

public interface Pizza {
    
    public String getDescription();
    
    public double getCost();
    
}


/* 
public abstract class Pizza{

    
    public abstract void setDescription(String newDescription);
    public abstract String getDescription();
    
    public abstract void setCost(double newCost);
    public abstract double getCost();
    
    // I could use getter and setter methods for every 
    // potential Pizza topping
    
}
*/

 • ThreeCheesePizza.java

// By going this route I'll have to create a new subclass
// for an infinite number of pizza.
// I'd also have to change prices in many classes 
// when just 1 Pizza topping cost changes

// Inheritance is static while composition is dynamic
// Through composition I'll be able to add new functionality
// by writing new code rather than by changing current code

public class ThreeCheesePizza extends Pizza{

    private String description = "Mozzarella, Fontina, Parmesan Cheese Pizza";
    private double cost = 10.50;
    
    public void setDescription(String newDescription) {
        
        description = newDescription;
        
    }

    public String getDescription() {
    
        return description;
        
    }

    public void setCost(double newCost) {
        
        cost = newCost;
        
    }

    public double getCost() {
        
        return cost;
        
    }
}

 • PlainPizza.java

// Implements the Pizza interface with only the required
// methods from the interface

// Every Pizza made will start as a PlainPizza

public class PlainPizza implements Pizza {
 
    public String getDescription() {
        
        return "Thin dough";
    
    }

    public double getCost() {

        System.out.println("Cost of Dough: " + 4.00);
        
        return 4.00;
    
    }
 
}

 • ToppingDecorator.java

// Has a "Has a" relationship with Pizza. This is an
// Aggregation Relationship

abstract class ToppingDecorator implements Pizza {

    protected Pizza tempPizza;
    
    // Assigns the type instance to this attribute
    // of a Pizza
    
    // All decorators can dynamically customize the Pizza
    // instance PlainPizza because of this
    
    public ToppingDecorator(Pizza newPizza){
        
        tempPizza = newPizza;
        
    }
    
    public String getDescription() {
        
        return tempPizza.getDescription();
        
    }

    public double getCost() {
        
        return tempPizza.getCost();
        
    }
    
}

 • Mozzarella.java

public class Mozzarella extends ToppingDecorator {

    public Mozzarella(Pizza newPizza) {
        
        super(newPizza);
        
        System.out.println("Adding Dough");
        
        System.out.println("Adding Moz");
    }
    
    // Returns the result of calling getDescription() for
    // PlainPizza and adds " mozzarella" to it
    
    public String getDescription(){
        
        return tempPizza.getDescription() + ", mozzarella";
        
    }
    
    public double getCost(){
        
        System.out.println("Cost of Moz: " + .50);
        
        return tempPizza.getCost() + .50;
        
    }
    
}

 • TomatoSauce.java

public class TomatoSauce extends ToppingDecorator {

    public TomatoSauce(Pizza newPizza) {
        super(newPizza);
        
        System.out.println("Adding Sauce");
    }
    
    // Returns the result of calling getDescription() for
    // PlainPizza, Mozzarella and then TomatoSauce
    
    public String getDescription(){
        
        return tempPizza.getDescription() + ", tomato sauce";
        
    }
    
    public double getCost(){
        
        System.out.println("Cost of Sauce: " + .35);
        
        return tempPizza.getCost() + .35;
        
    }
    
}

 • PizzaMaker.java

public class PizzaMaker {
    
    public static void main(String[] args){
        
        // The PlainPizza object is sent to the Mozzarella constructor
        // and then to the TomatoSauce constructor
        
        Pizza basicPizza = new TomatoSauce(new Mozzarella(new PlainPizza()));
        
        System.out.println("Ingredients: " + basicPizza.getDescription());
        
        System.out.println("Price: " + basicPizza.getCost());
        
    }
    
}

Adapter

What is the Adapter Design Pattern?

• Allows 2 incompatible interfaces to work together.

• Used when the client expects a (target) interface.

• The Adapter class allows the use of the available interface and the Target interface.

• Any class can work together as long as the Adapter solves the issue that all classes must implement every method defined by the shared interface.

Sample Code

• EnemyAttacker.java

// This is the Target Interface : This is what the client
// expects to work with. It is the adapters job to make new 
// classes compatible with this one.

public interface EnemyAttacker {
    
    public void fireWeapon();
    
    public void driveForward();
    
    public void assignDriver(String driverName);
    
}

• EnemyTank.java

// EnemyTank implements EnemyAttacker perfectly
// Our job is to make classes with different methods
// from EnemyAttacker to work with the EnemyAttacker interface

import java.util.Random;

public class EnemyTank implements EnemyAttacker{
    
    Random generator = new Random();

    public void fireWeapon() {
        
        int attackDamage = generator.nextInt(10) + 1;
        
        System.out.println("Enemy Tank Does " + attackDamage + " Damage");
        
    }

    public void driveForward() {
        
        int movement = generator.nextInt(5) + 1;
        
        System.out.println("Enemy Tank moves " + movement + " spaces");
        
    }

    public void assignDriver(String driverName) {
        
        System.out.println(driverName + " is driving the tank");
        
    }
    
}

• EnemyRobot.java

// This is the Adaptee. The Adapter sends method calls
// to objects that use the EnemyAttacker interface
// to the right methods defined in EnemyRobot

import java.util.Random;

public class EnemyRobot{

    Random generator = new Random();
    
    public void smashWithHands() {
        
        int attackDamage = generator.nextInt(10) + 1;
        
        System.out.println("Enemy Robot Causes " + attackDamage + " Damage With Its Hands");
        
    }

    public void walkForward() {
        
        int movement = generator.nextInt(5) + 1;
        
        System.out.println("Enemy Robot Walks Forward " + movement + " spaces");
        
    }

    public void reactToHuman(String driverName) {
        
        System.out.println("Enemy Robot Tramps on " + driverName);
        
    }
    
    
    
}

• EnemyRobotAdapter.java

// The Adapter must provide an alternative action for 
// the the methods that need to be used because
// EnemyAttacker was implemented.

// This adapter does this by containing an object
// of the same type as the Adaptee (EnemyRobot)
// All calls to EnemyAttacker methods are sent
// instead to methods used by EnemyRobot

public class EnemyRobotAdapter implements EnemyAttacker{

    EnemyRobot theRobot;
    
    public EnemyRobotAdapter(EnemyRobot newRobot){
        
        theRobot = newRobot;
        
    }
    
    public void fireWeapon() {
        
        theRobot.smashWithHands();
        
    }

    public void driveForward() {
        
        theRobot.walkForward();
        
    }

    public void assignDriver(String driverName) {
        
        theRobot.reactToHuman(driverName);
        
    }
    
    
    
}

• TestEnemyAttackers.java

public class TestEnemyAttackers{
    
    public static void main(String[] args){
        
        EnemyTank rx7Tank = new EnemyTank();
        
        EnemyRobot fredTheRobot = new EnemyRobot();
        
        EnemyAttacker robotAdapter = new EnemyRobotAdapter(fredTheRobot);
        
        System.out.println("The Robot");
        
        fredTheRobot.reactToHuman("Paul");
        fredTheRobot.walkForward();
        fredTheRobot.smashWithHands();
        System.out.println();
        
        System.out.println("The Enemy Tank");
        
        rx7Tank.assignDriver("Frank");
        rx7Tank.driveForward();
        rx7Tank.fireWeapon();
        System.out.println();
        
        System.out.println("The Robot with Adapter");
        
        robotAdapter.assignDriver("Mark");
        robotAdapter.driveForward();
        robotAdapter.fireWeapon();

    }
    
}

Facade

What is the Facade Design Pattern?

• When you create a simplified interface that performs many other actions behind the scenes.

• Can I withdrawal $50 from the bank?

• Check if the checking account is valid.

• Check if the security code is valid.

• Check if funds are available.

• Make changes accordingly.

Sample Code

• WelcomeToBank.java

public class WelcomeToBank{
    
    public WelcomeToBank() {
        
        System.out.println("Welcome to ABC Bank");
        System.out.println("We are happy to give you your money if we can find it
");
        
        
    }
    
}

• AccountNumberCheck.java

public class AccountNumberCheck{
    
    private int accountNumber = 12345678;
    
    public int getAccountNumber() { return accountNumber; }
    
    public boolean accountActive(int acctNumToCheck){
        
        if(acctNumToCheck == getAccountNumber()) {
            
            return true;
            
        } else {
            
            return false;
            
        }
        
    }
    
}

• SecurityCodeCheck.java

public class SecurityCodeCheck {
    
    private int securityCode = 1234;
    
    public int getSecurityCode() { return securityCode; }
    
    public boolean isCodeCorrect(int secCodeToCheck){
        
        if(secCodeToCheck == getSecurityCode()) {
            
            return true;
            
        } else {
            
            return false;
            
        }
        
    }
    
}

• FundsCheck.java

public class FundsCheck {
    
    private double cashInAccount = 1000.00;
    
    public double getCashInAccount() { return cashInAccount; }
    
    public void decreaseCashInAccount(double cashWithdrawn) { cashInAccount -= cashWithdrawn; }
    
    public void increaseCashInAccount(double cashDeposited) { cashInAccount += cashDeposited; }
    
    public boolean haveEnoughMoney(double cashToWithdrawal) {
        
        if(cashToWithdrawal > getCashInAccount()) {
            
            System.out.println("Error: You don't have enough money");
            System.out.println("Current Balance: " + getCashInAccount());
            
            return false;
            
        } else {
            
            decreaseCashInAccount(cashToWithdrawal);
            
            System.out.println("Withdrawal Complete: Current Balance is " + getCashInAccount());
            
            return true;
            
        }
        
    }
    
    public void makeDeposit(double cashToDeposit) {
        
        increaseCashInAccount(cashToDeposit);
        
        System.out.println("Deposit Complete: Current Balance is " + getCashInAccount());
        
    }
    
}

• BankAccountFacade.java

// The Facade Design Pattern decouples or separates the client 
// from all of the sub components

// The Facades aim is to simplify interfaces so you don't have 
// to worry about what is going on under the hood

public class BankAccountFacade {
    
    private int accountNumber;
    private int securityCode;
    
    AccountNumberCheck acctChecker;
    SecurityCodeCheck codeChecker;
    FundsCheck fundChecker;
    
    WelcomeToBank bankWelcome;
    
    public BankAccountFacade(int newAcctNum, int newSecCode){
        
        accountNumber = newAcctNum;
        securityCode = newSecCode;
        
        bankWelcome = new WelcomeToBank();
        
        acctChecker = new AccountNumberCheck();
        codeChecker = new SecurityCodeCheck();
        fundChecker = new FundsCheck();
        
    }
    
    public int getAccountNumber() { return accountNumber; }
    
    public int getSecurityCode() { return securityCode; }
    
    
    public void withdrawCash(double cashToGet){
        
        if(acctChecker.accountActive(getAccountNumber()) &&
                codeChecker.isCodeCorrect(getSecurityCode()) &&
                fundChecker.haveEnoughMoney(cashToGet)) {
                    
                    System.out.println("Transaction Complete
");
                    
                } else {
                    
                    System.out.println("Transaction Failed
");
                    
                }
        
    }
    
    
    public void depositCash(double cashToDeposit){
        
        if(acctChecker.accountActive(getAccountNumber()) &&
                codeChecker.isCodeCorrect(getSecurityCode())) {
            
                    fundChecker.makeDeposit(cashToDeposit);
                    
                    System.out.println("Transaction Complete
");
                    
                } else {
                    
                    System.out.println("Transaction Failed
");
                    
                }
        
    }
    
}

• TestBankAccount.java

public class TestBankAccount {
    
    public static void main(String[] args){
        
        BankAccountFacade accessingBank = new BankAccountFacade(12345678, 1234);
        
        accessingBank.withdrawCash(50.00);
        
        accessingBank.withdrawCash(990.00);
        
    }
    
}

Bridge

What is the Bridge Design Pattern?

• Decouple an abstraction from its implementation so that the two can vary independently.

• The Bridge Design Pattern is very poorly explained.

• Everyone seems to explain it differently.

• Progressively adding functionality while separating out major differences using abstract classes.

When to use the Bridge Design Pattern?

• When you want to be able to change both the abstractions (abstract classes) and concrete classes independently.

• When you want the first abstract class to define rules (Abstract TV).

• The concrete class adds additional rules (Concrete TV).

• An abstract class has a reference to the device and it defines abstract methods that will be defined (Abstract Remote).

• The Concrete Remote defines the abstract methods required.

Sample Code

• EntertainmentDevice.java

// Implementor
// With the Bridge Design Pattern you create 2 layers of abstraction
// In this example I'll have an abstract class representing
// different types of devices. I also have an abstract class
// that will represent different types of remote controls

// This allows me to use an infinite variety of devices and remotes

abstract class EntertainmentDevice {
    
    public int deviceState;
    
    public int maxSetting;
    
    public int volumeLevel = 0;
    
    public abstract void buttonFivePressed();
    
    public abstract void buttonSixPressed();
    
    public void deviceFeedback() {
        
        if(deviceState > maxSetting || deviceState < 0) { deviceState = 0; }
        
        System.out.println("On Channel " + deviceState);
        
    }
    
    public void buttonSevenPressed() {
        
        volumeLevel++;
        
        System.out.println("Volume at: " + volumeLevel);
        
    }
    
    public void buttonEightPressed() {
        
        volumeLevel--;
        
        System.out.println("Volume at: " + volumeLevel);
        
    }
    
}

• TVDevice.java

// Concrete Implementor

// Here is an implementation of the EntertainmentDevice
// abstract class. I'm specifying what makes it different
// from other devices

public class TVDevice extends EntertainmentDevice {
    
    public TVDevice(int newDeviceState, int newMaxSetting){
        
        deviceState = newDeviceState;
        
        maxSetting = newMaxSetting;
        
    }
    
    public void buttonFivePressed() {
        
        System.out.println("Channel Down");
        
        deviceState--;
        
    }

    public void buttonSixPressed() {
        
        System.out.println("Channel Up");
        
        deviceState++;
        
    }
    
}

• RemoteButton.java

// Abstraction

// This is an abstract class that will represent numerous
// ways to work with each device

public abstract class RemoteButton{
    
    // A reference to a generic device using aggregation
    
    private EntertainmentDevice theDevice;
    
    public RemoteButton(EntertainmentDevice newDevice){
        
        theDevice = newDevice;
        
    }
    
    public void buttonFivePressed() {
        
        theDevice.buttonFivePressed();
        
    }
    
    public void buttonSixPressed() {
        
        theDevice.buttonSixPressed();
        
    }
    
    public void deviceFeedback(){
        
        theDevice.deviceFeedback();
        
    }
    
    public abstract void buttonNinePressed();
    
}

• TVRemoteMute.java

// Refined Abstraction

// If I decide I want to further extend the remote I can

public class TVRemoteMute extends RemoteButton{
    
    public TVRemoteMute(EntertainmentDevice newDevice) {
        super(newDevice);
    }
    
    public void buttonNinePressed() {
        
        System.out.println("TV was Muted");
        
    }
    
}

• TVRemotePause.java

// Refined Abstraction

// If I decide I want to further extend the remote I can

public class TVRemotePause extends RemoteButton{
    
    public TVRemotePause(EntertainmentDevice newDevice) {
        super(newDevice);
    }
    
    public void buttonNinePressed() {
        
        System.out.println("TV was Paused");
        
    }
    
}

• TestTheRemote.java

public class TestTheRemote{
    
    public static void main(String[] args){
        
        RemoteButton theTV = new TVRemoteMute(new TVDevice(1, 200));
        
        RemoteButton theTV2 = new TVRemotePause(new TVDevice(1, 200));
        
        // HOMEWORK --------------
        
        RemoteButton theDVD = new DVDRemote(new DVDDevice(1,14));
        
        // -----------------------
        
        System.out.println("Test TV with Mute");
        
        theTV.buttonFivePressed();
        theTV.buttonSixPressed();
        theTV.buttonNinePressed();
        
        System.out.println("
Test TV with Pause");
        
        theTV2.buttonFivePressed();
        theTV2.buttonSixPressed();
        theTV2.buttonNinePressed();
        theTV2.deviceFeedback();
        
        // HOMEWORK
        
        System.out.println("
Test DVD");
        
        theDVD.buttonFivePressed();
        theDVD.buttonSixPressed();
        theDVD.buttonNinePressed();
        theDVD.buttonNinePressed();
        
    }
    
}

Flyweight

What is the Flyweight Design Pattern?

• Used when you need to create a large number of similar objects.

• To reduce memory usage you share objects that are similar in some way rather than creating new ones.

• Intrinsic State: Color.

• Extrinsic State: Size.

Sample Code

• FlyWeightTest.java

// The Flyweight design pattern is used when you need to
// create a large number of similar objects

// To reduce memory this pattern shares Objects that are 
// the same rather than creating new ones

import javax.swing.*;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;

public class FlyWeightTest extends JFrame{

    private static final long serialVersionUID = 1L;

    JButton startDrawing;
    
    int windowWidth = 1750;
    int windowHeight = 1000;
    
    // A new rectangle is created only if a new color is needed
    
    Color[] shapeColor = {Color.orange, Color.red, Color.yellow,
            Color.blue, Color.pink, Color.cyan, Color.magenta,
            Color.black, Color.gray};
    
    public static void main(String[] args){
        
        new FlyWeightTest();
        
    }
    
    public FlyWeightTest(){
        
        // Create the frame, position it and handle closing it
        
        this.setSize(windowWidth,windowHeight);
        this.setLocationRelativeTo(null);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setTitle("Flyweight Test");
        
        JPanel contentPane = new JPanel();
        
        contentPane.setLayout(new BorderLayout());
        
        final JPanel  drawingPanel  = new JPanel();
        
        startDrawing = new JButton("Button 1");
        
        contentPane.add(drawingPanel,  BorderLayout.CENTER);
        
        contentPane.add(startDrawing, BorderLayout.SOUTH);
        
        startDrawing.addActionListener(new ActionListener() {
            
            public void actionPerformed(ActionEvent event) {
                Graphics g = drawingPanel.getGraphics();
                
                
                long startTime = System.currentTimeMillis();
                
                
                for(int i=0; i < 100000; ++i) {
                    
                    // 
                    // Uses rectangles stored in the HashMap to
                    // speed up the program
                    
                    MyRect rect = RectFactory.getRect(getRandColor());
                    rect.draw(g, getRandX(), getRandY(), 
                            getRandX(), getRandY());
                    
                    // 
                    /*
                    MyRect rect = new MyRect(getRandColor(), getRandX(), getRandY(), getRandX(), getRandY());
                    rect.draw(g);
                    */
                    

                    // 
                    /*
                    g.setColor(getRandColor());
                    g.fillRect(getRandX(), getRandY(), getRandX(), getRandY());
                    */
                    
                    
                }
                
                long endTime = System.currentTimeMillis();

                System.out.println("That took " + (endTime - startTime) + " milliseconds");
                
             }
          });
        
        this.add(contentPane);
        
        this.setVisible(true);
        
    }
    
    // Picks random x & y coordinates
    
    private int getRandX(){ return (int)(Math.random()*windowWidth); }
    
    private int getRandY(){ return (int)(Math.random()*windowHeight); }
    
    // Picks a random Color from the 9 available
    
    private Color getRandColor(){ 
        Random randomGenerator = new Random();
        
        int randInt = randomGenerator.nextInt(9);
        
        return shapeColor[randInt]; 
        
    }
    
}

• MyRect.java

import java.awt.*;
public class MyRect {
   private Color color = Color.black;
   private int x, y, x2, y2;
   
   public MyRect(Color color) {
       
       this.color = color;
       
   }
   
   public void draw(Graphics g, int upperX, int upperY, int lowerX, int lowerY) {
          g.setColor(color);
          g.fillRect(upperX, upperY, lowerX, lowerY);
   }
   
   /* Original forces creation of a rectangle every time
     
   public MyRect(Color color, int upperX, int upperY, int lowerX, int lowerY) {
      this.color = color;
      this.x = upperX;   
      this.y = upperY;
      this.x2 = lowerX; 
      this.y2 = lowerY;
   }
   
   public void draw(Graphics g) {
      g.setColor(color);
      g.fillRect(x, y, x2, y2);
   }
   */
}

• RectFactory.java

// This factory only creates a new rectangle if it 
// uses a color not previously used

// Intrinsic State: Color
// Extrinsic State: X & Y Values

import java.util.HashMap;
import java.awt.Color;
public class RectFactory {
    
    // The HashMap uses the color as the key for every 
    // rectangle it will make up to 8 total
    
    private static final HashMap<Color, MyRect> rectsByColor = new HashMap<Color, MyRect>();
   
    public static MyRect getRect(Color color) {
        MyRect rect = (MyRect)rectsByColor.get(color);
        
        // Checks if a rectangle with a specific
        // color has been made. If not it makes a
        // new one, otherwise it returns one made already
        
        if(rect == null) {
            rect = new MyRect(color);
            
            // Add new rectangle to HashMap
            
            rectsByColor.put(color, rect);
         
        }
        return rect;
    }
}

Proxy

What is the Proxy Design Pattern?

• Provide a class which will limit access to another class.

• You may do this for security reasons, because an Object is intensive to create, or is accessed from a remote location.

Sample Code

• ATMMachine.java

public class ATMMachine implements GetATMData{
    
    
    public ATMState getYesCardState() { return hasCard; }
    public ATMState getNoCardState() { return noCard; }
    public ATMState getHasPin() { return hasCorrectPin; }
    public ATMState getNoCashState() { return atmOutOfMoney; }
    
    // NEW STUFF
    
    public ATMState getATMState() { return atmState; }
    public int getCashInMachine() { return cashInMachine; }
}

• GetATMData.java

// This interface will contain just those methods
// that you want the proxy to provide access to

public interface GetATMData {
  public ATMState getATMState();
  public int getCashInMachine();
}

• ATMProxy.java

// In this situation the proxy both creates and destroys
// an ATMMachine Object

public class ATMProxy implements GetATMData {

    // Allows the user to access getATMState in the 
    // Object ATMMachine
    
    public ATMState getATMState() {
        
        ATMMachine realATMMachine = new ATMMachine();
        
        return realATMMachine.getATMState();
    }

    // Allows the user to access getCashInMachine 
    // in the Object ATMMachine
    
    public int getCashInMachine() {
        
        ATMMachine realATMMachine = new ATMMachine();
        
        return realATMMachine.getCashInMachine();
        
    }
    
}

• TestATMMachine.java

public class TestATMMachine {
    
    public static void main(String[] args){
        
        ATMMachine atmMachine = new ATMMachine();
        
        atmMachine.insertCard();
        
        atmMachine.ejectCard();
        
        atmMachine.insertCard();
        
        atmMachine.insertPin(1234);
        
        atmMachine.requestCash(2000);
        
        atmMachine.insertCard();
        
        atmMachine.insertPin(1234);
        
        // NEW STUFF : Proxy Design Pattern Code
        // The interface limits access to just the methods you want
        // made accessible

        GetATMData realATMMachine = new ATMMachine();
        
        GetATMData atmProxy = new ATMProxy();
        
        System.out.println("
Current ATM State " + atmProxy.getATMState());
        
        System.out.println("
Cash in ATM Machine $" + atmProxy.getCashInMachine());
        
        // The user can't perform this action because ATMProxy doesn't
        // have access to that potentially harmful method
        // atmProxy.setCashInMachine(10000);
        
    }
    
}

• ATMState.java

public interface ATMState {
    
    void insertCard();
    void ejectCard();
    void insertPin(int pinEntered);
    void requestCash(int cashToWithdraw);
    
}

作者：netoxi
出处：http://www.cnblogs.com/netoxi
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