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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