Chain of Responsibility Pattern

Pros

• Multiple objects can handle a request without knowing which at runtime

Cons

• A performance impact from going through multiple objects for a request
• Can be difficult to debug

Example Explanation

LoanApprover - Has a member field containing the next link in a chain of responsibilities for fulfilling a request by the client

Manager - Concrete implementation of a LoanApprover. If an expense is too high for a manager to approve it uses if the next LoanApprover in the chain is capable of approving a loan

class Main {
  public static void main(String[] args) {

    LoanApprover man = new Manager();
    LoanApprover dir = new Director();
    LoanApprover vice = new VicePresident();
    LoanApprover pres = new President();

    man.setNextApprover(dir);
    dir.setNextApprover(vice);
    vice.setNextApprover(pres);

    man.approveLoan( new Loan(3312));
    man.approveLoan( new Loan(7500));
    man.approveLoan( new Loan(21250));
    man.approveLoan( new Loan(60000));
    man.approveLoan( new Loan(250000));

  }
}

abstract class LoanApprover {
  protected LoanApprover nextApprover;
  protected int approvalLimit;
  private String rank;

  public LoanApprover(String rank, int approvalLimit){
    this.rank = rank;
    this.approvalLimit = approvalLimit;
  }

  public void setNextApprover(LoanApprover nextApprover){
    this.nextApprover = nextApprover;
  }

  public void approveLoan(Loan loan){

    if (approvalLimit > loan.getAmount() ){
      System.out.println(rank+" approves loan of "+loan.getAmount());
      return;
    }
    nextApprover.approveLoan(loan);
  }
}

class Manager extends LoanApprover{
  public Manager(){
    super("Manager", 5000);
  }
}
class Director extends LoanApprover{
  public Director(){
    super("Director", 10000);
  }
}
class VicePresident extends LoanApprover{
  public VicePresident(){
    super("Vice President", 25000);
  }
}
class President extends LoanApprover{
  public President(){
    super("President", 100000);
  }
  @Override
  public void approveLoan(Loan loan){
    if(loan.getAmount() > approvalLimit){
      System.out.println("Loan of "+loan.getAmount()+" denied by President");
      return;
    }
    else{
      super.approveLoan(loan);
    }
  }
}

class Loan{
  private int amount;
  public Loan(int amount){
    this.amount = amount;
  }
  public int getAmount(){ return amount; }
}

Extra Resources

https://www.pluralsight.com/courses/patterns-library