/ Design Patterns / Behavioral patterns / Chain of Responsibility

Chain of Responsibility Design Pattern in Java

Lots of client effort to manage a list of Processors

interface Image {
    String process();
}

class IR implements Image {
    public String process() {
        return "IR";
    }
}

class LS implements Image {
    public String process() {
        return "LS";
    }
}

class Processor {
    private static final Random RANDOM = new Random();
    private static int nextID = 1;
    private int id = nextID++;

    public boolean execute(Image img) {
        if (RANDOM.nextInt(2) != 0) {
            System.out.println("   Processor " + id + " is busy");
            return false;
        }
        System.out.println("Processor " + id + " - " + img.process());
        return true;
    }
}

public class ChainDemo {
    public static void main( String[] args ) {
        Image[] inputImages = {new IR(), new IR(), new LS(), new IR(), new LS(), new LS()};
        Processor[] processors = {new Processor(), new Processor(), new Processor()};
        for (int i=0, j; i < inputImages.length; i++) {
            System.out.println("Operation #" + (i + 1) + ":");
            j = 0;
            while (!processors[j].execute(inputImages[i])) {
                j = (j + 1) % processors.length;
            }
            System.out.println();
        }
    }
}

Output

Operation #1:
   Processor 1 is busy
   Processor 2 is busy
   Processor 3 is busy
   Processor 1 is busy
   Processor 2 is busy
   Processor 3 is busy
   Processor 1 is busy
Processor 2 - IR

Operation #2:
   Processor 1 is busy
   Processor 2 is busy
Processor 3 - IR

Operation #3:
   Processor 1 is busy
   Processor 2 is busy
Processor 3 - LS

Operation #4:
   Processor 1 is busy
Processor 2 - IR

Operation #5:
   Processor 1 is busy
Processor 2 - LS

Operation #6:
Processor 1 - LS

Code examples

Java Chain of Responsibility in Java: Before and after Chain of Responsibility in Java
C++ Chain of Responsibility in C++ Chain of Responsibility in C++: Chain and Composite
PHP Chain of Responsibility in PHP
Python Chain of Responsibility in Python