[JAVA] [Gang of Four] Design pattern learning --Bridge

Bridge-Bridge

** Table of Contents ** Normally, the part that can be extracted is an abstract class, and the other parts are implemented by a concrete class that inherits the abstract class.

This pattern separates the abstract class from the concrete class so that the implementation of the abstract class can be decided at runtime.

Take an icon class that manages information about icons as an example. First ** monochrome icon class (abstract class) ** and ** large monochrome icon class (concrete class) ** for displaying monochrome icons in various sizes **, ** medium monochrome icon class (concrete class) * *, ** Implement small monochrome icon class (concrete class) **. However, due to an unplanned specification change from the client, it became necessary to implement ** color icon class (abstract class) ** that allows RGB to be set freely on the way. Of course, the icon must meet the specifications for displaying three types, large, medium, and small, like the monochrome icon.

When the abstract class and the concrete class are permanently combined by inheritance, ** color icon class ** inherited ** large color icon class **, ** medium color icon class ** ... omitted

You will have to create all large to small icons that inherit the color icon class. When adding more clear icons, do the same ... Omitted

Is it a similar idea to create an intermediate table and normalize a table with many-to-many relations in DB?

Purpose

Separate the extracted classes and implementations so that they can be modified independently.

Component

· Abstraction abstract class -A class that extends the RefinedAbstraction Abstraction class ・ Implementor concrete class -A class that extends the ConcreteImplementor Implementor class

Implementation

First, implement the monochrome icon class and color icon class of the abstract class.

Abstraction abstract class

Abstract icon class This class is the heart of the so-called pattern, the ** bridge ** of the abstract and concrete classes.

AbstIcon.kt

package bridge

abstract class AbstIcon(iconType: IconType) {
    enum class IconType(val value: String) {
        BlackAndWhite("Monochrome icon"),
        Color("Color icon")
    }

    private var bigIcon: ImpIcon = BigIcon(iconType)
    private var middleIcon: ImpIcon = MiddleIcon(iconType)
    private var smallIcon: ImpIcon = SmallIcon(iconType)

    abstract fun getType(): String

    fun getBigIcon(): ImpIcon {
        return bigIcon
    }

    fun getMiddleIcon(): ImpIcon {
        return middleIcon
    }

    fun getSmallIcon(): ImpIcon {
        return smallIcon
    }
}

A class that extends the RefinedAbstraction Abstraction class

Monochrome icon abstract class

AbstBlackAndWhiteIcon.kt

package bridge

class AbstBlackAndWhiteIcon: AbstIcon(IconType.BlackAndWhite) {
    override fun getType(): String {
        return AbstIcon.IconType.BlackAndWhite.value
    }

    //Monochrome icon original processing various
}

Color icon abstract class

AbstColorIcon.kt

package bridge

class AbstColorIcon: AbstIcon(IconType.Color) {

    override fun getType(): String {
        return AbstIcon.IconType.Color.value
    }

    //Various color icon original processing
}

Next, create concrete classes such as large icons, medium icons, and small icons.

Implementor concrete class

Concrete icon interface

ImpIcon.kt

package bridge

interface ImpIcon {
    enum class IconSize(val value: String) {
        Big("Large icon"),
        Middle("Medium icon"),
        Small("Small icon")
    }

    fun getIcon(): String
}

A class that extends the ConcreteImplementor Implementor class

Large, medium and small icon classes

BigIcon.kt

package bridge

class BigIcon(iconType: AbstIcon.IconType): ImpIcon {

    private val iconType = iconType

    override fun getIcon(): String {
        return "【type】:" + iconType.value + "【size】:" + ImpIcon.IconSize.Big.value
    }

}

MiddleIcon.kt

package bridge

class MiddleIcon(iconType: AbstIcon.IconType): ImpIcon {

    private val iconType = iconType

    override fun getIcon(): String {
        return "【type】:" + iconType.value + "【size】:" + ImpIcon.IconSize.Middle.value
    }
}

SmallIcon.kt

package bridge

class SmallIcon(iconType: AbstIcon.IconType): ImpIcon {

    private val iconType = iconType

    override fun getIcon(): String {
        return "【type】:" + iconType.value + "【size】:" + ImpIcon.IconSize.Small.value
    }
}

The person who uses each icon

Client.kt

package bridge

class Client {
    init {
        val colorIcon = AbstColorIcon()
        println(colorIcon.getType())
        println(colorIcon.getBigIcon().getIcon())
        println(colorIcon.getMiddleIcon().getIcon())
        println(colorIcon.getSmallIcon().getIcon())

        val blackAndWhiteIcon = AbstBlackAndWhiteIcon()
        println(blackAndWhiteIcon.getType())
        println(blackAndWhiteIcon.getBigIcon().getIcon())
        println(blackAndWhiteIcon.getMiddleIcon().getIcon())
        println(blackAndWhiteIcon.getSmallIcon().getIcon())
    }
}

This completes the implementation of the sample code using the icon.

Output result

[output]
Color icon
[Type]: Color icon [Size]: Large icon
[Type]: Color icon [Size]: Medium icon
[Type]: Color icon [Size]: Small icon
Monochrome icon
[Type]: Monochrome icon [Size]: Large icon
[Type]: Monochrome icon [Size]: Medium icon
[Type]: Monochrome icon [Size]: Small icon

Now let's add a clear icon with a transparent background. In the conventional method, ** large clear eye ** ... is abbreviated, but in this pattern, it can be realized only by implementing AbstClearIcon class` `` which inherits AbstIcon class` ``. ..

AbstClearIcon.kt

package bridge

class AbstClearIcon: AbstIcon(IconType.Clear) {

    override fun getType(): String {
        return AbstIcon.IconType.Clear.value
    }

    //Clear icon original processing various
}

Add the following code to the Client class and try again.

Client.kt

    val clearIcon = AbstClearIcon()
    println(clearIcon.getType())
    println(clearIcon.getBigIcon().getIcon())
    println(clearIcon.getMiddleIcon().getIcon())
    println(clearIcon.getSmallIcon().getIcon())

[output]
Color icon
[Type]: Color icon [Size]: Large icon
[Type]: Color icon [Size]: Medium icon
[Type]: Color icon [Size]: Small icon
Monochrome icon
[Type]: Monochrome icon [Size]: Large icon
[Type]: Monochrome icon [Size]: Medium icon
[Type]: Monochrome icon [Size]: Small icon
Clear icon
[Type]: Clear icon [Size]: Large icon
[Type]: Clear icon [Size]: Medium icon
[Type]: Clear icon [Size]: Small icon

It was easy to expand.

This makes it possible to easily implement it no matter how much the abstract class side increases or the concrete class side increases.