Decorator pattern in LLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the base component interface.

LLD

interface [1] {
    void operation();
}

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AComponent

BClient

CConcreteComponent

DDecorator

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Decorator' as the base interface name instead of 'Component'.

Naming the interface after the concrete implementation.

The base interface is named Component which defines the operation method to be decorated.

2fill in blank

medium

Complete the code to declare the decorator class that implements the component interface.

LLD

class [1] implements Component {
    protected Component component;
    public [1](Component component) {
        this.component = component;
    }
    public void operation() {
        component.operation();
    }
}

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ADecorator

BConcreteDecorator

CConcreteComponent

DClient

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'ConcreteDecorator' as the decorator class name here.

Not implementing the component interface.

The decorator class is named Decorator and it implements the Component interface, forwarding calls to the wrapped component.

3fill in blank

hard

Fix the error in the concrete decorator's operation method to add extra behavior.

LLD

class ConcreteDecorator extends Decorator {
    public ConcreteDecorator(Component component) {
        super(component);
    }
    public void operation() {
        [1];
        super.operation();
    }
}

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Asuper.operation()

Bcomponent.operation()

CextraBehavior()

Doperation()

Attempts:

3 left

💡 Hint

Common Mistakes

Calling component.operation() directly instead of using super.operation().

Calling operation() recursively causing infinite loop.

The concrete decorator adds extra behavior by calling extraBehavior() before delegating to the base operation.

4fill in blank

hard

Fill both blanks to implement a decorator that adds logging before and after the operation.

LLD

class LoggingDecorator extends Decorator {
    public LoggingDecorator(Component component) {
        super(component);
    }
    public void operation() {
        System.out.println([1]);
        super.operation();
        System.out.println([2]);
    }
}

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A"Start operation"

B"End operation"

C"Operation started"

D"Operation finished"

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the start and end messages.

Using the same message for both prints.

The logging decorator prints "Start operation" before and "End operation" after the base operation.

5fill in blank

hard

Fill all three blanks to create a client code that wraps a concrete component with two decorators.

LLD

Component component = new ConcreteComponent();
Component decorated = new [1](component);
Component doubleDecorated = new [2](decorated);
doubleDecorated.[3]();

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ALoggingDecorator

BConcreteDecorator

Coperation

DDecorator

Attempts:

3 left

💡 Hint

Common Mistakes

Using the base Decorator class directly instead of concrete decorators.

Calling a method other than operation.

The client wraps the ConcreteComponent first with ConcreteDecorator, then with LoggingDecorator, and calls operation() on the outermost decorator.