デザインパターン学習メモ：「Chain of Responsibility」

// Handler役
// 処理を担当するクラス（抽象クラス）
public abstract class Support {
    private Support successor; // 次に処理を試みる後続のオブジェクト

    public Support() {
    }

    public void setSuccessor(Support support) {
        this.successor = support;
    }

    public void resolve(EventType type) {
        if (successor != null) {
            successor.resolve(type);
        } else {
            System.out.println("NOBODY RESOLVED");
        }
    }
}

// ConcreteHandler役
// 処理を担当するクラス（Handler役を継承）
public class FooSupport extends Support {
    private static final EventType SUPPORT_TYPE = EventType.FOO;

    public FooSupport() {
        super();
    }

    @Override
    public void resolve(EventType type) {
        if (type == SUPPORT_TYPE) {
            System.out.println("RESOLVED by FooSupport");
        } else {
            super.resolve(type);
        }
    }
}

// ConcreteHandler役
// 処理を担当するクラス（Handler役を継承）
public class BarSupport extends Support {
    private static final EventType SUPPORT_TYPE = EventType.BAR;

    public BarSupport() {
        super();
    }

    @Override
    public void resolve(EventType type) {
        if (type == SUPPORT_TYPE) {
            System.out.println("RESOLVED by BarSupport");
        } else {
            super.resolve(type);
        }
    }
}

// 要求のタイプ
// Handlerに処理を依頼するときに用いられる
public enum EventType {
    FOO, BAR, BAZ
}

public class Main {
    public static void main(String[] args) {
        Support fooSupport = new FooSupport();
        fooSupport.setSuccessor(new BarSupport());

        fooSupport.resolve(EventType.FOO);
        fooSupport.resolve(EventType.BAR);
        fooSupport.resolve(EventType.BAZ);
    }
}

RESOLVED by FooSupport
RESOLVED by BarSupport
NOBODY RESOLVED