An example of the Delegate design pattern in Java.

DelegateExample.java

/** An example of the Delegate design pattern in Java. */
interface DelegateExample {

  /** Main method to demonstrate the delegate pattern. */
  static void main(String[] args) {
    Contract implementation = new Implementation();
    Contract delegator = new Delegator(implementation);
    delegator.performAction("Test Input");
  }

  /** The contract interface defining the method to be implemented. */
  interface Contract {

    /** Performs an action with the given input. */
    void performAction(String input);
  }

  /** The concrete implementation of the contract. */
  final class Implementation implements Contract {

    @Override
    public void performAction(String input) {
      System.out.println("Action performed with input: " + input);
    }
  }

  /** Forwards calls to the delegate implementation. */
  final class Delegator implements Contract {

    private final Contract delegate;

    Delegator(final Contract delegate) {
      this.delegate = delegate;
    }

    @Override
    public void performAction(String input) {
      System.out.println("Delegating action...");
      delegate.performAction(input);
    }
  }
}