Multiple Inheritance of State and Implementation

Today, I was just curious about why an enum can not extend anything else. I took a look on the Oracle document here, and I found the answer is below:

"All enums implicitly extend java.lang.Enum. Because a class can only extend one parent (see Declaring Classes), the Java language does not support multiple inheritance of state (see Multiple Inheritance of State, Implementation, and Type), and therefore an enum cannot extend anything else."

I have been learned of it before. But, wait a sec...! Why Java does not support multiple inheritance of state?

Since I have worked with other programming languages like C++, I was able to make a class extend some other classes.

The short answer is to avoid the issues of multiple inheritance of state. I wonder if other programming languages have these below terms but Java does.

Multiple inheritance of state

It is the ability to inherit fields from multiple classes. There is a problem and Java avoids it.

"For example, suppose that you are able to define a new class that extends multiple classes. When you create an object by instantiating that class, that object will inherit fields from all of the class's superclasses. What if methods or constructors from different superclasses instantiate the same field?"

Multiple inheritance of implementation

It is the ability to inherit method definitions from multiple classes.

There is a similar problem that sometimes compiler cannot determine which member or method to access or invoke. Java deals with that problem as below.

"As with multiple inheritance of implementation, a class can inherit different implementations of a method defined (as default or static) in the interfaces that it extends. In this case, the compiler or the user must decide which one to use."

I just did a quick test for the above explaination

Conclusion, Java supports multiple inheritance of implementation but multiple inheritance of state.

Reference
[1]. https://docs.oracle.com/javase/tutorial/java/javaOO/enum.html
[2]. https://docs.oracle.com/javase/tutorial/java/IandI/multipleinheritance.html

Comments

Math fundamentals and Katex

It was really tough for me to understand many articles about data science due to the requirements of understanding mathematics (especially linear algebra). I’ve started to gain some basic knowledges about Math by reading a book first. The great tool Typora and stackedit with supporting Katex syntax simply helps me to display Math-related symbols. Let’s start! The fundamental ideas of mathematics: “doing math” with numbers and functions. Linear algebra: “doing math” with vectors and linear transformations. 1. Solving equations Solving equations means finding the value of the unknown in the equation. To find the solution, we must break the problem down into simpler steps. E.g: x 2 − 4 = 4 5 x 2 − 4 + 4 = 4 5 + 4 x 2 = 4 9 x = 4 9 ∣ x ∣ = 7 x = 7 or x = − 7 \begin{aligned} x^2 - 4 &= 45\\ x^2 - 4 + 4 &= 45 + 4\\ x^2 &= 49\\ \sqrt{x}&=\sqrt{49}\\ |x| &= 7\\ x=7 &\text{ or } x=-7 \end{aligned} x 2 − 4 x 2 − 4 + 4 x 2 x ∣ x ∣ x = 7 = 4 5 = 4 ...

Styling Sort Icons Using Font Awesome for Primefaces' Data Table

So far, Primefaces has used image sprites for displaying the sort icons. This leads to a problem if we want to make a different style for these icons; for example, I would make the icon "arrow up" more blurry at the first time the table loading because I want to highlight the icon "arrow down". I found a way that I can replace these icons with Font Awesome icons. We will use "CSS Pseudo-classes" to achieve it. The hardest thing here is that we should handle displaying icons in different cases. There is a case both "arrow up" and "arrow down" showing and other case is only one of these icons is shown. .ui-sortable-column-icon.ui-icon.ui-icon-carat-2-n-s { background-image: none; margin-left: 5px; font-size: 1.1666em; position: relative; } .ui-sortable-column-icon.ui-icon.ui-icon-carat-2-n-s:not(.ui-icon-triangle-1-s)::before { content: "\f106"; font-family: "FontAwesome"; position: ...

Sharing a virtualenv across several Python projects using Pipenv

There is a standard library for all projects in Python. However, several projects don’t always have the same dependencies all the time. That is where virtual environments come to play. You can follow this official document to use two separated tools virtualenv and pip to fulfill that need. My preferred alternative is to use pipenv . Pipenv is easy to use and convenient. The following are my steps to make a shared virtualenv for my all projects which requires the same dependencies. Step 1. Create an isolated virtualenv. python -m venv my-shared-env Step 2. Create a symbolic link to the created virtualenv. cd project_1 ln -s ~/.local/share/virtualenvs/my-shared-env .venv I have encountered the following issue at step 1. FileNotFoundError: [Errno 2] No such file or directory: '{my_project_path}/.venv/bin/pip': '{my_project_path}/.venv/bin/pip' The root cause was I tried to create virtualenv by running pipenv install and renaming the generated virtualenv to ...

When we don't see the sun, we see other stars

What are your motivations for creativity? - I want to make a change. - It makes me happy! It is a need of my mind. How to be creative for a thing? There are two steps: - See the thing as every people see it - Think about a new different thing from it How to think about a new different thing? There are two ways: - Forget all things you have already known. - A whack on the side of your head. ;) This was what I have learned from the following great book: source: Amazon.com Well! A physical whack on the side of your head is needed sometimes but the meaning behind is that you need to break these 9 following locks on your mind. Remove them! The lock #1: "The correct answer" We all learn from schools that there is only one correct answer to a question. For example, a proposition is only true or false in Algebra. In reality, there are always some answers to a question basing on a point of view. For example, number 6 becomes number 9 if you look it ...

Updates to the Scrum Guide - The 5 Scrum Values

This article is available at blog.scrum.org , here I just quote my favorite points and give my comment at the end of this post. Ken Schwaber and Jeff Sutherland, the creators of Scrum delivered a webinar on their latest update to the Scrum Guide . The update was a simple one, adding the 5 values of Scrum to the Guide: These values sound easy? Well, there are many misunderstandings and common problems when applying these values. Here are some example: Value Misunderstanding Getting the value right Commitment Committing to something that you don’t understand because you are told to by your boss. Committing yourself to the team and Sprint Goal. Focus Focusing on keeping the customer happy Being focused on the sprint and its goal. Openness Telling everyone everything about all your work Highlighting when you have challenges and problems that are stopping you from success Respect Thinking you are helping the team by being a hero Helping peop...

vhandit

Search This Blog