Awhile ago, I put together a package for doing what you want, and more. (I needed it for a utility I was writing). It uses the ASM library. You can use reflection, but ASM turned out to perform better. I put my package in an open source library I have on my web site. The … Read more
With <out T>, you can treat the interface reference as one upwards in the hierarchy. With <in T>, you can treat the interface reference as one downwards in the hiearchy. Let me try to explain it in more english terms. Let’s say you are retrieving a list of animals from your zoo, and you intend … Read more
Because interfaces specify only what the class is doing, not how it is doing it. The problem with multiple inheritance is that two classes may define different ways of doing the same thing, and the subclass can’t choose which one to pick.
No, there is no way to implement the same method in two different ways in one class in Java. That can lead to many confusing situations, which is why Java has disallowed it. interface ISomething { void doSomething(); } interface ISomething2 { void doSomething(); } class Impl implements ISomething, ISomething2 { void doSomething() {} // … Read more
An abstract class is a class which cannot be instantiated. An abstract class is used by creating an inheriting subclass that can be instantiated. An abstract class does a few things for the inheriting subclass: Define methods which can be used by the inheriting subclass. Define abstract methods which the inheriting subclass must implement. Provide … Read more
I have been searching for a while and there seems to be different approaches, here is a summary: reflections library is pretty popular if u don’t mind adding the dependency. It would look like this: Reflections reflections = new Reflections(“firstdeveloper.examples.reflections”); Set<Class<? extends Pet>> classes = reflections.getSubTypesOf(Pet.class); ServiceLoader (as per erickson answer) and it would look … Read more
You can achieve what you want without the instanceof keyword as you can write custom type guards now: interface A{ member:string; } function instanceOfA(object: any): object is A { return ‘member’ in object; } var a:any={member:”foobar”}; if (instanceOfA(a)) { alert(a.member); } Lots of Members If you need to check a lot of members to determine … Read more
You can extend TextView to set custom fonts as I learned here. TextViewPlus.java: package com.example; import android.content.Context; import android.content.res.TypedArray; import android.graphics.Typeface; import android.util.AttributeSet; import android.util.Log; import android.widget.TextView; public class TextViewPlus extends TextView { private static final String TAG = “TextView”; public TextViewPlus(Context context) { super(context); } public TextViewPlus(Context context, AttributeSet attrs) { super(context, attrs); setCustomFont(context, … Read more
Interfaces are just contracts or signatures and they don’t know anything about implementations. Coding against interface means, the client code always holds an Interface object which is supplied by a factory. Any instance returned by the factory would be of type Interface which any factory candidate class must have implemented. This way the client program … Read more
There’s a lot more to abstract classes than default method implementations (such as private state), but as of Java 8, whenever you have the choice of either, you should go with the defender (aka. default) method in the interface. The constraint on the default method is that it can be implemented only in the terms … Read more