Structural_Decorator

🛠️

• add behavior to object dynamically without modifying their class
• wrap an object with another object(decorator)

✅ Structure and Diagram

👀

• Like in HTML, we decorate text like <b> <u> <i> Text </i> </u> </b>

Component ➡️ BoldDecorator ➡️ UnderlineDecorator ➡️ ItalicDecorator

1. Base Component(interface)

• common interface

interface Text{
    String getContent();
}

2. Concrete Component

• base implementation

class PlainText implements Text{
    private String content;

    public PlainText(String content){
        this.content = content;
    }

    @Override
    public String getContent(){
        return content;
    }
}

3. Base Decorator

• holds a reference to the wrapped component

abstract class TextDecorator implements Text{
    protected Text text;

    public TextDecorator(Text text){
        this.text = text;
    }

    @Override
    public String getContent(){
        return text.getContent();
    }
}

4. Concrete Decorators

• extends the base decorator and behavior

class BoldDecorator extends TextDecorator{
    public BoldDecorator(Text text){
        super(text);
    }

    @Override
    public String getContent(){
        return "<b>" + super.getContent() + "</b>";
    }
}

class UnderlineDecorator extends TextDecorator{
    public UnderlineDecorator(Text text){
        super(text);
    }

    @Override
    public String getContent(){
        return "<u>" + super.getContent() + "</u>";
    }
}

class ItalicDecorator extends TextDecorator{
    public ItalicDecorator(Text text){
        super(text);
    }

    @Override
    public String getContent(){
        return "<i>" + super.getContent() + "</i>";
    }
}

5. Using the decorators in main class

public class Main{
    psvm{
        Text plainText = new PlainText("hello"); //hello
        Text boldText = new BoldDecorator(new PlainText("hello")); //<b> hello </b>
        Text boldUnderlineItalicText = new BoldDecorator(new UnderlineDecortator(new ItalicDecorator(new PlainText("hello")))); //<b> <u> <i> hello </i> </u> </b>

    }
}

🛠️

DataInputStream in =
    new DataInputStream(
        new BufferedInputStream(
            new FileInputStream("data.txt")
        )
    );

• InputStream → Component
• FileInputStream → Concrete component
• FilterInputStream → Decorator base class
• BufferedInputStream, DataInputStream → Concrete decorators