Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.
Participants
- Component: defines the interface for objects that can have responsibilities added to them dynamically.
- ConcreteComponent: defines an object to which additional responsibilities can be attached.
- Decorator: maintains a reference to a Component object and defines an interface that conforms to Component's interface.
- ConcreteDecorator: adds responsibilities to the component.
Code
public class Main { public static void main(String[] args) { ConcreteComponent c = new ConcreteComponent(); ConcreteDecoratorA d1 = new ConcreteDecoratorA(); ConcreteDecoratorB d2 = new ConcreteDecoratorB(); d1.setComponent(c); d2.setComponent(d1); d2.operation(); } } public interface Component { void operation(); } public class ConcreteComponent implements Component { @Override public void operation() { System.out.println("ConcreteComponent.operation()"); } } public abstract class Decorator implements Component { protected Component component; public void setComponent(Component component) { this.component = component; } @Override public void operation() { if (component != null) { component.operation(); } } } public class ConcreteDecoratorA extends Decorator { private static final String ADDED_STATE = "ConcreteDecoratorA.operation()"; @Override public void operation() { super.operation(); System.out.println(ADDED_STATE); } } public class ConcreteDecoratorB extends Decorator { @Override public void operation() { super.operation(); addedBehavior(); System.out.println("ConcreteDecoratorB.operation()"); } private void addedBehavior() { System.out.println("ConcreteDecoratorB.addedBehavior()"); } } Output
ConcreteComponent.operation() ConcreteDecoratorA.operation() ConcreteDecoratorB.addedBehavior() ConcreteDecoratorB.operation() 
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