The façade pattern is a software engineering design pattern commonly used with Object-oriented programming.
A facade is an object that provides a simplified interface to a larger body of code, such as a class library. A facade can:
- make a software library easier to use and understand, since the facade has convenient methods for common tasks;
- make code that uses the library more readable, for the same reason;
- reduce dependencies of outside code on the inner workings of a library, since most code uses the facade, thus allowing more flexibility in developing the system;
- wrap a poorly-designed collection of APIs with a single well-designed API (as per task needs).
Structure
- Facade
- The facade class interacts Packages 1, 2, and 3 with the rest of the application.
- Clients
- The objects using the Facade Pattern to access resources from the Packages.
- Packages
- Software library / API collection accessed through the Facade Class.
Examples
Java
This is an abstract example of how a client ("you") interacts with a façade (the "computer") to a complex system (internal computer parts, like CPU and HardDrive).
/* 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) {
...
}
}
/* Façade */
class Computer {
public void startComputer() {
cpu.freeze();
memory.load(BOOT_ADDRESS, hardDrive.read(BOOT_SECTOR, SECTOR_SIZE));
cpu.jump(BOOT_ADDRESS);
cpu.execute();
}
}
/* Client */
class You {
public static void main(String[] args) {
Computer facade = new Computer();
facade.startComputer();
}
}
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