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Java refactoring: removing duplicate code

Posted on 2014-07-24
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Last Modified: 2014-07-24
In the following scenario I have:

interface IClassA

abstract class ClassA implements IClassA

concrete classes ClassB1 and ClassB2 extend ClassA


ClassB1 and ClassB2 both have methods DoStuff()

The code for DoStuff() is identical in both ClassB1 and ClassB2

Is it possible to refactor this to get rid of the identical code?

public interface IClassA {

	public int DoStuff();
	public int ClassSpecific();
}



public abstract class ClassA implements IClassA {

	//public ClassA(){}
	
	public void aCommonMethod() {
	}
}



public class ClassB1 extends ClassA {
	
	public ClassB1(){}
	

	@Override
	public int DoStuff() 
	{
		return ClassSpecific();
	}


	@Override
	public int ClassSpecific()
	{
		return 9;
	}
}



public class ClassB2 extends ClassA {

	public ClassB2(){}

	
	@Override
	public int DoStuff() 
	{
		return ClassSpecific();
	}
	
	
	@Override
	public int ClassSpecific()
	{
		return 5;
	}
}

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(Imagine DoStuff() is a lot more complicated than it is here, but it does have buried in it a call to ClassSpecific().)
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Question by:deleyd
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7 Comments
 
LVL 26

Accepted Solution

by:
dpearson earned 500 total points
Comment Utility
Can you not just move DoStuff() to classA?

Doug
0
 

Author Comment

by:deleyd
Comment Utility
Here's my real doStuff() class:
    public double getValueAs(TemperatureUnits units) { 
		if (units == TemperatureUnits.FAHRENHEIT) {
            return asFahrenheit().doubleValue();
        }
        else if (units == TemperatureUnits.CELSIUS) {
            return asCelsius().doubleValue();
        }
        else if (units == TemperatureUnits.KELVIN) {
            return asKelvin().doubleValue();
        }
        else
        {
            throw new InvalidParameterException("Unhanded Temperature Unit " + units.toString());
        }
    }

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methods asFahrenheit(), asCelsius(), asKelvin() are the Class Specific methods.

Moving the code to the abstract superclass (ClassA), it complains, because the superclass doesn't define asFahrenheit, asCelsius, asKelvin.
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LVL 16

Expert Comment

by:krakatoa
Comment Utility
Make the methods static in the abstract class then.
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Author Comment

by:deleyd
Comment Utility
I get:

"Cannot make a static reference to the non-static method ClassSpecific() from type IClassA."
0
 
LVL 26

Expert Comment

by:dpearson
Comment Utility
In that case I think you'll want to define
asFahrenheit, asCelsius, asKelvin
in the interface/abstract class as well.

You'll need a common "something" (abstract class/interface) for the shared code to be able to call common methods like "asCelsius" and have them execute the right specific implementation.

As you say, since the code is identical this should be solvable with the right hierarchy.  But the interface (or abstract class) will need to include all of the methods that are shared between the two concrete classes.

Doug
0
 

Author Closing Comment

by:deleyd
Comment Utility
I was missing the keyword 'abstract' !

I had public class AbstractClass

Now it works great once I noticed that. Thank you!
0
 
LVL 16

Expert Comment

by:krakatoa
Comment Utility
Well done Doug! ;)
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