CODEWITHSUNDEEP
javaspringspring-mvcdesign-patterns
Farrukh Chishti
Farrukh Chishti

Reputation: 8457

Design pattern for calling different functions for different instances

I have a java code like this-

Sample obj;
if(obj instanceOf Class1) 
{
    method1(obj);
} else if(obj instanceOf Class2) 
{
    method2(obj);
} else if(obj instanceOf Class3) 
{
    method3(obj);
}

Class1, Class2 and Class3 are actually DTO's and they are children of Sample, so I don't want to write business logic in DTO's.

I want to write the logic of method1, mehtod2 and method3 in a different class. Is there a design pattern for that. I am using spring MVC.

Basically, I am looking for some non-java technique to call the appropriate based on the instance instead of checking with instanceOf every single time.

Upvotes: 2

Views: 2197

Answers (3)

Hemant Patel
Hemant Patel

Reputation: 3260

Not a good one but let's try

  • Create an Interface

    public interface Processor {

    void process(Simple simple);

    }

  • Write implementation for each subclass of Sample // Class1 Processor public class Class1Processor implements Processor {

    @Override
public void process(Simple simple) {
    System.out.println("Class1 processing completed");
}

    } // Class2 Processor public class Class2Processor implements Processor {

    @Override
public void process(Simple simple) {
    System.out.println("Class2 processing completed");
}

    }

  • Processor Factory Class public class ProcessorFactory {

    private static final Map<Class<? extends Simple>, Processor> LOOKUP = new HashMap<>();

static {
    LOOKUP.put(Class1.class, new Class1Processor());
    LOOKUP.put(Class2.class, new Class2Processor());
}

public static <T extends Simple> Processor getProcessor(T obj) {
    return LOOKUP.get(obj.getClass());
}

    }

  • And Lastly Main Class public static void main(String[] args) {

    Simple class1 = new Class1();
Simple class2 = new Class2();

ProcessorFactory.getProcessor(class1).process(class1);
ProcessorFactory.getProcessor(class2).process(class2);

    }

Upvotes: 2

Abdullah Tellioglu
Abdullah Tellioglu

Reputation: 1474

How about create a custom annotation for classes? Does this solve your problem about business logic etc. Something like

@CustomMethodName(method="method1")
public class Class1{
 //..
}
@CustomMethodName(method="method2")
public class Class2{
 //..
}
@CustomMethodName(method="method3")
public class Class3{
 //..
}

After you should get your method name by using 

Class<?> aClass = Sample.class;
Annotation[] annotations = aClass.getAnnotations();
for(Annotation annotation : annotations){
    if(annotation instanceof CustomMethodName){
        CustomMethodName myAnnotation = (CustomMethodName) annotation;
        String methodName = myAnnotation.method();
        java.lang.reflect.Method method;
        try {
           method = obj.getClass().getMethod(methodName);// get method wherever you define them
           method.invoke(obj);//execute method
        } catch (SecurityException e) { ... }
          catch (NoSuchMethodException e) { ... }
     }
}

Upvotes: 1

Elliott Frisch
Elliott Frisch

Reputation: 201497

Define a method interface and implement the common interface in Class1, Class2 and Class3 - delegate to method1, method2 or method3 as appropriate in the implementation in those classes. Program to the common interface.

obj.method();

Upvotes: 2

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