Can anyone explain how this memory leak in Java/Android works in detail?

Question

I have been doing Java development for a long time, but I am ashamed to say I still don't have a good grasp on how memory leaks actually takes place. I however have no experience with Android development. Take the following code for example taken from this presentation: I have the following questions (please note that I am new to Android, but this example is not primarily focused on Android) How is memory leak even possible here ? The author says that its because the inner class is not marked as static and it will hold a reference to the outer class. So if I keep creating objects of the outer class like so: MainActivity one = new MainActivity(); one.onCreate(bundle); MainActivity two = new MainActivity(); two.onCreate(bundle); MainActivity three = new MainActivity(); three.onCreate(bundle); How does it matter ? If I am not wrong about how static references work, then only one object of LeakClass is created, right ? Unless a separate classloader is involved, right ? Is the memory leak only possible here because of how Android works ? If I were to manually create these objects then this would not be a problem right ? Please help me with an ELI5 explanation here, I am really unable to understand how this works. Thanks. JavaScript questions and answers, JavaScript questions pdf, JavaScript question bank, JavaScript questions and answers pdf, mcq on JavaScript pdf, JavaScript questions and solutions, JavaScript mcq Test , Interview JavaScript questions, JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)

Answer 1

Because LeakClass is an inner class, it has an inherent reference to the instance of the outer class that owns it. Since you're storing that value in a static variable, that means you're storing a reference to the outer class in that static transitively. Storing an Activity in a static is ALWAYS a leak, and ALWAYS a bad idea. Activities aren't singletons, you cannot assume there will only be one of them. If you don't need that parent reference, you can make it a static inner class. Static inner classes do not have an implicit outer reference, but cannot access member variables of functions of the owning class. Or you can make it a standalone, non-inner class (the two are equally good solutions). If you do need that parent reference, you cannot store it in a static variable without a leak. Figure out another way to make that data available.