A quick guide on the Facade design pattern

What is it?

The Facade design pattern is a commonly used pattern which pretty much every programming language API uses for general usage. In this design pattern, you use a single class to hide the details of a complex object, or even a set of classes. For example, java.net.InetAddress, its purpose is to connect to a specific URL and retrieve information about the host, etc. however it hides all of the complex detail (ex. using DNS to get the IP address of a host).

Simple example from Wikipedia:

Code:

/* Complex parts */ 
class CPU {
    public void freeze() { ... }
    public void jump(long position) { ... }
    public void execute() { ... }
}
 
class Memory {
    public void load(long position, byte[] data) { ... }
}
 
class HardDrive {
    public byte[] read(long lba, int size) { ... }
}
 
/* Facade */
 
class ComputerFacade {
    private CPU processor;
    private Memory ram;
    private HardDrive hd;
 
    public ComputerFacade() {
        this.processor = new CPU();
        this.ram = new Memory();
        this.hd = new HardDrive();
    }
 
    public void start() {
        processor.freeze();
        ram.load(BOOT_ADDRESS, hd.read(BOOT_SECTOR, SECTOR_SIZE));
        processor.jump(BOOT_ADDRESS);
        processor.execute();
    }
}
 
/* Client */
 
class You {
    public static void main(String[] args) {
        ComputerFacade computer = new ComputerFacade();
        computer.start();
    }
}

If you have any questions, feel free to ask me! ​

 

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