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 Design Patterns > Java Design Patterns > Builder

Builder 

Builder comes under creational design pattern. The intention is to build a complex object step by step.

Behaviour & Advantages

  • Separates the construction of a complex object from its representation so that the same construction process can create different representations.
  • Can alter the object construction process easily.
  • Separates the object construction process from its representation.
Participants
  • Builder
    Abstract interface for creating parts of complex product.
  • Concrete Builder
    An implementation of Builder which assembles the parts of product.
  • Director
    It controls the object construction process and flow. Internally it depends on Builder to assemble the final product.
  • Product
    The object to be constructed using builder.

In this example we are going to build a complex product (PersonalComputer) using builder pattern. Class IPCBuilder represents a builder. Classes HighCostPCBuilder, LowCostPCBuilder are two implementations of IPCBuilder. Class PCSeller acts as a director which controls the PC construction process.

File Name  :  
com/bethecoder/tutorials/dp/builder/PersonalComputer.java 
   
package com.bethecoder.tutorials.dp.builder;

public class PersonalComputer {

  private String motherboard;
  private String processor;
  private String hardDisk;
  private String monitor;
  
  private String ram;
  private String mouse;
  private String keyboard;
  
  public String getMotherboard() {
    return motherboard;
  }
  
  public void setMotherboard(String motherboard) {
    this.motherboard = motherboard;
  }
  
  public String getProcessor() {
    return processor;
  }
  
  public void setProcessor(String processor) {
    this.processor = processor;
  }
  
  public String getHardDisk() {
    return hardDisk;
  }
  
  public void setHardDisk(String hardDisk) {
    this.hardDisk = hardDisk;
  }
  
  public String getMonitor() {
    return monitor;
  }
  
  public void setMonitor(String monitor) {
    this.monitor = monitor;
  }
  
  public String getRam() {
    return ram;
  }
  
  public void setRam(String ram) {
    this.ram = ram;
  }
  
  public String getMouse() {
    return mouse;
  }
  
  public void setMouse(String mouse) {
    this.mouse = mouse;
  }
  
  public String getKeyboard() {
    return keyboard;
  }
  
  public void setKeyboard(String keyboard) {
    this.keyboard = keyboard;
  }
  
  public String toString() {
    StringBuilder sb = new StringBuilder();
    
    sb.append("----------- PC Configuration -----------");
    sb.append("\n Mother Board : ").append(motherboard);
    
    sb.append("\n Processor : ").append(processor);
    sb.append("\n Hard Disk : ").append(hardDisk);
    sb.append("\n Monitor : ").append(monitor);
    sb.append("\n RAM : ").append(ram);
    sb.append("\n Mouse : ").append(mouse);
    sb.append("\n Keyboard : ").append(keyboard);
    
    return sb.toString();
  }
}
   

The PC Builder interface is shown below,

File Name  :  
com/bethecoder/tutorials/dp/builder/IPCBuilder.java 
   
package com.bethecoder.tutorials.dp.builder;

public interface IPCBuilder {

  /**
   * Setup motherboard.
   */
  public void setupMotherBoard();
  
  /**
   * Setup RAM and processor.
   */
  public void setupProcessor();
  
  /**
   * Setup hard disk.
   */
  public void setupHardDisk();
  
  /**
   * Input peripherals - keyboard, mouse
   * Output peripherals - monitor 
   */
  public void setupPeripherals();
  
  /**
   * Get the fully constructed PC.
   
   @return PersonalComputer
   */
  public PersonalComputer getPC();
  
}
   

High Cost PC Builder implementation is shown below,

File Name  :  
com/bethecoder/tutorials/dp/builder/HighCostPCBuilder.java 
   
package com.bethecoder.tutorials.dp.builder;

/**
 * High Cost PC Builder Implementation 
 */
public class HighCostPCBuilder implements IPCBuilder {

  private PersonalComputer personalComputer = null;
  
  public HighCostPCBuilder() {
    this.personalComputer = new PersonalComputer();
  }
  
  @Override
  public PersonalComputer getPC() {
    return personalComputer;
  }

  @Override
  public void setupHardDisk() {
    personalComputer.setHardDisk("500 GB Hard disk");    
  }

  @Override
  public void setupMotherBoard() {
    personalComputer.setMotherboard("GigaByte GA-X58A-UD3R Desktop Motherboard");
  }

  @Override
  public void setupPeripherals() {
    personalComputer.setKeyboard("Logitech Multimedia Keyboard");
    personalComputer.setMouse("Logitech G9 Laser Mouse");
    personalComputer.setMonitor("19 inch LCD monitor");
  }

  @Override
  public void setupProcessor() {
    personalComputer.setProcessor("Intel P4 processor");
    personalComputer.setRam("4 GB");
  }

}
   

Low Cost PC Builder implementation is shown below,

File Name  :  
com/bethecoder/tutorials/dp/builder/LowCostPCBuilder.java 
   
package com.bethecoder.tutorials.dp.builder;

/**
 * Low Cost PC Builder Implementation 
 */
public class LowCostPCBuilder implements IPCBuilder {

  private PersonalComputer personalComputer = null;
  
  public LowCostPCBuilder() {
    this.personalComputer = new PersonalComputer();
  }
  
  @Override
  public PersonalComputer getPC() {
    return personalComputer;
  }

  @Override
  public void setupHardDisk() {
    personalComputer.setHardDisk("40 GB Hard disk");    
  }

  @Override
  public void setupMotherBoard() {
    personalComputer.setMotherboard("Asus A7N8X-LA Motherboard");
  }

  @Override
  public void setupPeripherals() {
    personalComputer.setKeyboard("Logitech Standard Keyboard");
    personalComputer.setMouse("Logitech Wireless Mouse M215");
    personalComputer.setMonitor("15 inch LCD monitor");
  }

  @Override
  public void setupProcessor() {
    personalComputer.setProcessor("Intel P3 processor");
    personalComputer.setRam("512 MB");
  }

}
   

The director implementation is shown below,

File Name  :  
com/bethecoder/tutorials/dp/builder/PCSeller.java 
   
package com.bethecoder.tutorials.dp.builder;

public class PCSeller {

  public static PersonalComputer getPC(IPCBuilder pcBuilder) {
    
    /**
     * Build PC Step by Step
     * The construction process/flow is
     * controlled by this class.
     */
    pcBuilder.setupMotherBoard();
    pcBuilder.setupProcessor();
    pcBuilder.setupHardDisk();
    pcBuilder.setupPeripherals();
    
    return pcBuilder.getPC();
  }
}
   

Builder usage is shown below,

File Name  :  
com/bethecoder/tutorials/dp/builder/Test.java 
   
package com.bethecoder.tutorials.dp.builder;

public class Test {

  /**
   @param args
   */
  public static void main(String[] args) {

    System.out.println(PCSeller.getPC(new LowCostPCBuilder()));
    System.out.println();
    System.out.println(PCSeller.getPC(new HighCostPCBuilder()));
  }

}
   

It gives the following output,
----------- PC Configuration -----------
 Mother Board : Asus A7N8X-LA Motherboard
 Processor : Intel P3 processor
 Hard Disk : 40 GB Hard disk
 Monitor : 15 inch LCD monitor
 RAM : 512 MB
 Mouse : Logitech Wireless Mouse M215
 Keyboard : Logitech Standard Keyboard

----------- PC Configuration -----------
 Mother Board : GigaByte GA-X58A-UD3R Desktop Motherboard
 Processor : Intel P4 processor
 Hard Disk : 500 GB Hard disk
 Monitor : 19 inch LCD monitor
 RAM : 4 GB
 Mouse : Logitech G9 Laser Mouse
 Keyboard : Logitech Multimedia Keyboard


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