Hi2all. I’am reading a Java book and got to the chapter about StreamAPI classes. So, my questions is: why in terminal operation methods using lower bounded wildcards, like: Indeed, in fact, you can use unbounded wildcards like this: Is there any reason to use exactly lower- bounded wildcards? Answer You cannot use unbounded wildcards for these methods. Suppose you are
How to not persist sqlSession.selectOne returned value?
My goal is to not persist the SqlSession.selectOne returned value. The problem is, if you do a sqlSession.selectOne (using an API endpoint) and then you edit the database directly for example using the MySQL workbench. After you edit the database and do another API endpoint request, the returned value will not change. This is how you recreate the problem: Do
How to get text from same Text Field used multiple times in Java Swing
I’m trying to get text from a JTextField iterated through my code (apparently, I can’t add a different text field from a button). Here’s what the “Add Items” button do: It adds two new text fields in the panel using FlowLayout. Now, I want to get the text given by the user from text fields with each one assigned to
How to join several validation annotations
I have following annotation to validate password: But spring validation does not recognize this rules. I used this annotation as: How can I get it without defining ConstraintValidator instance? Answer If you want to use ConstraintValidator, you can do it like this: create Password annotation : then create the PasswordConstraintValidator class : Then apply it to one of your fields,
A rare usage of WeakReference?
I have a class whose instances are initialized and used by underlying flatform. Nothing’s wrong and I thought I need to add some static methods for being used as method references. Still nothing seems wrong (I believe) and I don’t like the instance persisted with the class and that’s why I’m trying to do this. I basically don’t even know
False sharing and volatile
Good day, I recently found an annotation introduced in Java 8 called Contended. From this mailing list I read what is false sharing and how annotation allows objects or fields to allocate an entire cache line. After some research I found that if two cores store the same cache line and one of them modify it then the second one
How to expand a number to match another in Java
I’m given a number for example 319 and i need to write code that will break out a number to 3192310, for example. I’ll try to explain how it needs to be done and what i’ve tried. Explanation: (given two inputs: 319 and 3192310) So the program starts by appending 0 to 9 at the end of 319, and compares
Java Generics – quick question on Greater Than Method with Objects
I have an assignment in my Java class, we are learning Generics, I have looked in my notes, my lessons, and even on the internet and I still cant figure out what this last assignment question is asking me to do, which is: Write a generic “greater-than” function that takes two objects as arguments, each of which has a “value”
Why don’t size and preferredSize make this label bigger?
I’m building up a panel that will go in a larger program; the following program still illustrates my question, but it looks a bit more complicated than it absolutely has to because there are places I will add things later. I would like the currentImageLabel to be a standard size; I intend for it to get different images put into
How to do translate animation of button in Android Studio?
I am trying to move a button from one site to another. I manage to move it but when it moves, I have to click on the place where it was before instead of hitting the button. Why does this happen? This is how it looks. You can see how at the end when I click on another side, the