Reducing code duplication in constructors of subclasses - java

SO here's the situation. I am extending a class in Java and I Need to provide 3 constructors with 1, 2 and 3 parameters respectively.
public class MessageButton extends ImageButton {
private String number;
public MessageButton(Context context) {
super(context);
}
public MessageButton(Context context, AttributeSet attrs) {
super(context, attrs);
if( attrs.getAttributeValue("uk.co.gsteinert.ssbb", "number") != null ) {
this.number = attrs.getAttributeValue("uk.co.gsteinert.ssbb", "number");
}
}
public MessageButton(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
if( attrs.getAttributeValue("uk.co.gsteinert.ssbb", "number") != null ) {
this.number = attrs.getAttributeValue("uk.co.gsteinert.ssbb", "number");
}
}
}
Obviously there's a bit of duplication there (in the last two constructors) and I want to reduce this.
I see two options:
Move the code into a setup() function, and call that from each constructor. This reduces the duplicated code, but still requires the call in each constructor.
Use this() in all but the last constructor. The only issue is that the defaults for the optional parameters are not null. I would need to check the source of the superclass to work out what values to use.
SO the way I see it, either way I have to duplicate code (the function call) or make assumptions about the superclass (the default values). I know both of these are less than desirable but which is the greater evil?
Or am I missing something?
Thanks


As you mentioned, I would use this() for all your constructors and check which default values are used in the parent class and supply those instead of null (used in this example). You are using this class for your custom code, so you should know what values you want as default.
public class MessageButton extends ImageButton {
private String number;
public MessageButton(Context context) {
this(context, null);
}
public MessageButton(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public MessageButton(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
if (attrs.getAttributeValue("uk.co.gsteinert.ssbb", "number") != null) {
this.number = attrs.getAttributeValue("uk.co.gsteinert.ssbb", "number");
}
}
}


You can call one constructor from another (without creating a new instance) with this
public MyClass(String value) {
....
}
public MyClass() {
this(defaultValue);
}


public class MessageButton extends ImageButton {
private String number;
public MessageButton(Context context) {
this(context,null,0);
}
public MessageButton(Context context, AttributeSet attrs) {
this(context, attrs,0);
}
public MessageButton(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
if(attrs!=null){
if( attrs.getAttributeValue("uk.co.gsteinert.ssbb", "number") != null ) {
this.number = attrs.getAttributeValue("uk.co.gsteinert.ssbb", "number");
}
}}
}

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Now i understand what you are asking. Ideal solution for your problem would be AOP (aspect oriented programming).
These should help you:
https://medium.com/#jdvp/aspect-oriented-programming-in-android-159054d52757
https://fernandocejas.com/2014/08/03/aspect-oriented-programming-in-android/
This lib should help you:
https://www.eclipse.org/aspectj/

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super(context);
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{
super(context, attrs);
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Try this, and let me know if this works

java construct method overload with multi match

Refer to the code below:
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thanks

Sure, just cast the null into the signature type!
new ExpandableTextView(context, (AttributeSet)null, (Runnable)null)

Your code should not work as Compiler will throw error mentioning ambiguous method. Because Java will always try to use the most specific applicable version of a method that's available (see JLS ยง15.12.2). And null is a valid value for the types Context, AttributeSet and Runnable. Therefore all 3 version are applicable.

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