Command pattern in LLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the Command interface method.

LLD

interface Command {
    void [1]();
}

Drag options to blanks, or click blank then click option'

Aexecute

Brun

Cstart

Dcall

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names like run or start which are not standard in Command pattern.

Leaving the method name empty or incorrect.

The Command interface defines the execute method which all commands implement.

2fill in blank

medium

Complete the code to implement the execute method in a concrete command.

LLD

class LightOnCommand implements Command {
    private Light light;

    public LightOnCommand(Light light) {
        this.light = light;
    }

    public void [1]() {
        light.on();
    }
}

Drag options to blanks, or click blank then click option'

Aexecute

Bcall

Cstart

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name different from the interface.

Not calling the receiver's method inside execute.

The concrete command implements the execute method to call the receiver's action.

3fill in blank

hard

Fix the error in the Invoker class to call the command properly.

LLD

class RemoteControl {
    private Command slot;

    public void setCommand(Command command) {
        this.slot = command;
    }

    public void buttonWasPressed() {
        slot.[1]();
    }
}

Drag options to blanks, or click blank then click option'

Acall

Brun

Cstart

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Calling a method name not defined in the Command interface.

Forgetting to call the method on the command object.

The Invoker calls the execute method on the command to perform the action.

4fill in blank

hard

Fill both blanks to complete the UndoableCommand interface extending Command and adding undo method.

LLD

interface UndoableCommand extends Command {
    void [1]();
    void [2]();
}

Drag options to blanks, or click blank then click option'

Aexecute

Bundo

Credo

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect method names like redo or run.

Not including execute method in the interface.

The UndoableCommand interface extends Command by adding undo method alongside execute.

5fill in blank

hard

Fill all three blanks to complete the Client code that creates a command, sets it to the invoker, and triggers execution.

LLD

Light light = new Light();
Command lightOn = new LightOnCommand([1]);
RemoteControl remote = new RemoteControl();
remote.[2](lightOn);
remote.[3]();

Drag options to blanks, or click blank then click option'

Alight

BsetCommand

CbuttonWasPressed

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Passing wrong object to command constructor.

Using wrong method names on the invoker.

Calling execute directly on the invoker.

The client creates a receiver light, a command with that receiver, sets the command on the invoker, and presses the button to execute.