Implements vs. Extends: When to Use Which in OOP?

When to Use "Implements" vs "Extends" in Object-Oriented Programming

In object-oriented programming, understanding the difference between "implements" and "extends" is crucial. While both keywords allow classes to inherit functionality, they have distinct purposes.

Implements Interface vs Extends Class

• Implements Interface: Used when a class agrees to provide implementations for methods declared in an interface. Interfaces define contracts that classes must fulfill by implementing the specified methods.
• Extends Class: Used when a class inherits the properties and methods of a parent class. It allows the subclass to reuse and extend the functionality of the parent class.

Key Differences

• Inheritance: Extends establishes a parent-child relationship, allowing the subclass to access the methods and variables defined in the parent class. Implements, on the other hand, does not provide direct inheritance.
• Multiple Implementation: Interfaces support multiple inheritance in Java, allowing a class to implement multiple interfaces. Classes, however, only support single inheritance.
• Overriding vs Implementing: When implementing an interface, the class must provide implementations for all declared methods. When extending a class, the subclass can optionally override parent class methods to modify their behavior.

When to Use

• Implements: Use when you want a class to fulfill a specific contract defined by an interface, particularly if multiple inheritance is required.
• Extends: Use when you want to extend the functionality of an existing class and reuse its methods and variables.

Examples

• Implements:

  public interface Drawable {
    void draw();
  }
  
  public class Circle implements Drawable {
    @Override
    public void draw() {
        // Implement the circle drawing logic
    }
  }

• Extends:

  public class Base {
    private int value;
  
    public int getValue() {
        return value;
    }
  }
  
  public class Child extends Base {
    private String name;
  
    public String getName() {
        return name;
    }
  }

Understanding the nuances between "implements" and "extends" is essential for designing effective and maintainable Java code.

The above is the detailed content of Implements vs. Extends: When to Use Which in OOP?. For more information, please follow other related articles on the PHP Chinese website!