Piece movement rules (polymorphism) in LLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the base class method for movement.

LLD

class Piece {
    public void [1]() {
        // base movement logic
    }
}

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

Arun

Bmove

Cjump

Dwalk

Attempts:

3 left

💡 Hint

Common Mistakes

Using unrelated method names like 'run' or 'jump' which do not fit the context.

The base class method for piece movement is conventionally named 'move' to represent the action.

2fill in blank

medium

Complete the code to override the move method in a subclass.

LLD

class Knight extends Piece {
    @Override
    public void [1]() {
        // knight specific movement
    }
}

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

Ajump

Bwalk

Crun

Dmove

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name which does not override the base method.

The subclass overrides the base class method 'move' to provide specific movement rules.

3fill in blank

hard

Fix the error in the method signature to correctly override the base method.

LLD

class Bishop extends Piece {
    public void [1]() {
        // bishop movement logic
    }
}

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

Amove

BmoveTo

CmovePieceTo

DmovePiece

Attempts:

3 left

💡 Hint

Common Mistakes

Changing the method name breaks overriding and polymorphism.

To override correctly, the method name must be 'move' matching the base class method.

4fill in blank

hard

Fill both blanks to define an abstract base class and abstract move method.

LLD

abstract class Piece {
    public abstract void [1]();
}

class Queen extends Piece {
    @Override
    public void [2]() {
        // queen movement logic
    }
}

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

Amove

Brun

Cjump

Dwalk

Attempts:

3 left

💡 Hint

Common Mistakes

Using different method names breaks the abstract method contract.

The abstract method and its override must have the same name 'move' to enforce polymorphism.

5fill in blank

hard

Fill all three blanks to implement polymorphic move calls for different pieces.

LLD

Piece p1 = new [1]();
Piece p2 = new [2]();
p1.[3]();
p2.move();

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

AKnight

BBishop

Cmove

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect class names or method names breaks polymorphism.

Create instances of Knight and Bishop, then call the polymorphic 'move' method on each.

Practice

1. What is the main benefit of using polymorphism for piece movement rules in a game design?

easy

A. It allows each piece to have its own move logic without type checks.

B. It forces all pieces to share the same move logic.

C. It requires manual checking of piece types before moving.

D. It prevents pieces from moving on the board.

Solution

1. Step 1: Understand polymorphism concept

   Polymorphism allows different objects to be treated through a common interface while having their own behavior.

2. Step 2: Apply to piece movement

   Each piece class implements its own move() method, so no need to check piece type before moving.

3. Final Answer:

   It allows each piece to have its own move logic without type checks. -> Option A

4. Quick Check:

   Polymorphism = own move logic without type checks [OK]

Hint: Polymorphism means no type checks for moves [OK]

Common Mistakes:

• Thinking all pieces share the same move logic
• Believing manual type checks are needed
• Confusing polymorphism with inheritance only

2. Which of the following is the correct way to declare a base class method for piece movement in a polymorphic design?

easy

A. move(self): pass

B. def move(self): pass

C. def move(): pass

D. def move(self, board): return

Solution

1. Step 1: Recall method declaration syntax in Python

   Instance methods must have self as the first parameter.

2. Step 2: Identify correct method signature

   def move(self): pass correctly declares a method with self and no implementation.

3. Final Answer:

   def move(self): pass -> Option B

4. Quick Check:

   Method with self parameter = def move(self): pass [OK]

Hint: Instance methods always start with self parameter [OK]

Common Mistakes:

• Omitting self parameter in method
• Using incorrect syntax without def keyword
• Adding unnecessary parameters without context

3. Given the following code, what will be the output?

class Piece:
    def move(self):
        return "Base move"

class Knight(Piece):
    def move(self):
        return "L-shaped move"

pieces = [Piece(), Knight()]
for p in pieces:
    print(p.move())

medium

A. Base move\nL-shaped move

B. L-shaped move\nL-shaped move

C. Error: move() not implemented

D. Base move\nBase move

Solution

1. Step 1: Understand method overriding

   Subclass Knight overrides move() to return "L-shaped move".

2. Step 2: Trace the loop output

   First object is Piece, prints "Base move"; second is Knight, prints "L-shaped move".

3. Final Answer:

   Base move\nL-shaped move -> Option A

4. Quick Check:

   Base class and overridden subclass moves printed [OK]

Hint: Subclass method overrides base method output [OK]

Common Mistakes:

• Assuming base method always runs
• Expecting same output for all pieces
• Confusing method overriding with overloading

4. Identify the error in the following polymorphic piece movement code:

class Piece:
    def move(self):
        pass

class Bishop(Piece):
    def move():
        print("Diagonal move")

b = Bishop()
b.move()

medium

A. Cannot instantiate Bishop directly

B. Piece.move() should return a value

C. Bishop.move() missing self parameter

D. print statement syntax error

Solution

1. Step 1: Check method signatures

   Bishop.move() lacks self parameter, so it is not a proper instance method.

2. Step 2: Understand call context

   Calling b.move() passes self automatically, causing a TypeError due to missing parameter.

3. Final Answer:

   Bishop.move() missing self parameter -> Option C

4. Quick Check:

   Instance methods must have self parameter [OK]

Hint: Instance methods always need self parameter [OK]

Common Mistakes:

• Ignoring missing self in subclass method
• Thinking base class method must return value
• Assuming print syntax is wrong

5. You are designing a chess game using polymorphism for piece movement. How should you structure your classes to allow easy addition of new piece types without changing existing code?

hard

A. Write a single move() function with if-else for each piece type.

B. Implement move logic only in the base class and override rarely.

C. Use global variables to track piece types and moves.

D. Create a base Piece class with an abstract move() method; each piece subclass implements move().

Solution

1. Step 1: Apply polymorphism design principle

   Use a base class with an abstract or empty move() method to define interface.

2. Step 2: Implement subclasses for each piece

   Each piece subclass provides its own move() logic, enabling extension without modifying base code.

3. Final Answer:

   Create a base Piece class with an abstract move() method; each piece subclass implements move(). -> Option D

4. Quick Check:

   Base class + subclass move() = scalable design [OK]

Hint: Base class with abstract move() enables easy extension [OK]

Common Mistakes:

• Using if-else instead of polymorphism
• Relying on global variables for logic
• Putting all move logic in base class only