I try myself with design-patterns & -principles and have a question. Before, sorry for the bad coding-style habit !!
I have an interface like ITest in this case:
public interface ITest
{
public void method1();
}
and then implement the methods and fields, if any, into a concrete class B like this:
public class B implements ITest
{
//This is the method from the interface
@Override
public void method1()
{
System.out.println("method1");
}
//This is another method in class B
public void method2()
{
System.out.println("method2");
}
}
Now in the application code I put it in like this:
public class Main
{
public static void main(final String args[]) throws Exception
{
//One principle says:
//programm to an interface instead to an implementation
ITest test = new B();
//method from interface
test.method1();
//this method is not accessible because not part of ITest
test.method2(); //compile-time error
}
}
You see that method2() from class B is not available because to the interface of ITest. Now, what if I need this 'important' method? There are several possibilities. I could abstract it in the interface or make class B abstract and extend into another class and so on, or make the reference in the main() method like:
B test = new B();
But this would violate the principle. So, I modified the interface to:
public interface ITest
{
//A method to return the class-type B
public B hook();
public void method1();
}
And put in class B the implementation:
public class B implements ITest
{
//this returns the object reference of itself
@Override
public B hook()
{
return this;
}
//This is the method from the interface
@Override
public void method1()
{
System.out.println("method1");
}
//This is the 'important' method in class B
public void method2()
{
System.out.println("method2");
}
}
Now in my main()-method I can call both methods with a little hook or chaining mechanism without referencing a new object nor does it violate the design-principle and I don't need an extra class for extension or abstraction.
public class Main
{
public static void main(final String args[])
{
//programm to an interface instead into an implemintation
ITest test = new B();
//method from interface
test.method1();
//method2 will not be accessible from ITest so we referencing B through a method hook()
//benefits: we don't need to create extra objects nor additional classes but only referencing
test.hook().method2();
System.out.println("Are they both equal: "+test.equals(test.hook()));
}
}
Also, I can encapsulate, inherit and abstract other methods, fields etc. This means, that I can create more complex and flexible hierarchies.
My question now: Is this a kind of anti-pattern, bad design-principle or could we benefit from this?
Thank you for watching. :-)
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