final

This question already has an answer here: Java — private constructor vs final and more 3 answers As per my understanding Final class A final class is simply a class that can't be extended. A class with single no argument private constructor A class with private constructors cannot be instantiated except form inside that same class. This make it useless to extend it from another class. But it does not mean it cannot be sub classed at all, among inner classes we can extend and call the private constructor. So my understanding is, if we create a class with single no argument private constructor,

final修饰符的使用 　　1.修饰类： 　　　　final修饰的类不能被继承，final修饰的类里面的方法都是（隐式）final方法 　　2.修饰方法： 　　　　final修饰的方法不能被重写 　　3.修饰变量（被修饰的变量一定要进行初始赋值）： 　　　　1）基本类型变量： 　　　　　　　　final修饰的基本类型变量不能改变值 　　　　2）引用类型变量： 　　　　　　　　final修饰的引用类型变量的地址不能改变，即始终指向一个对象 　　 来源： https://www.cnblogs.com/shuaiBqi/p/11907908.html

Sorry, quick question here, just found something in my notes I don't understand in relation to making a method final. My notes claim you should make a method final for this reason : Makes it impossible to enforce invariants. A String should behave as a String. I don't really understand what is meant by this. Can someone please break it down for me ? Thanks a lot. I would guess that should have said "Make it possible to enforce invariants". Basically, if someone can override a method, then they can change behaviors affecting your class's invariants. There are typically two reasons to make a

I'm checking if the variable is initialized but at that point netbeans is giving me variable reader might not have been initialized warning. How do I fix/suppress this? This is my code (summary): final Reader reader; try { reader = new Reader(directory); //additional stuff that can cause an exception } catch (Exception ex) { //do stuff } finally { if (reader != null); } The point of the if check is to determine whether it is initialized. And what is the best practice for this? If reader was never initialized, it doesn't even have a null value. change final Reader reader; to Reader reader =

If I have code similar to the following: public Constructor(final Object o) { taskSystem.add(new CycleTask(15, 15, -1) { @Override public void execute() throws Throwable { //access o here every 15 cycles forever } }); } When would o be garbage collected, if ever? Only when the task has been collected, or will it remain in memory forever because it's final? o might get garbage collected once it is not reachable any longer, whether it is final or not. Obviously, as long as execute is running, if it needs to access o , it will prevent GC. When execute is done running, and assuming you have not