Yesterday, September 14, was the official release date of Java 17, the first Long Term Support (LTS) release in what feels like ages (the previous LTS release was Java 11, which came out three years ago).

One of the new features of Java 17 is the addition of sealed classes and interfaces. Which feels quite new to those who only program in Java, but hardly a surprise for those who also program in Scala.

I wrote last week that the future of Java is to absorb Scala features. Not every feature, of course, just the ones that are considered beneficial…

We’re less than a week away now from the official release of Java 17, the first Long Term Support (LTS) release of Java since Java 11. On September 14, 2021, the Java 17 runtime environment (JRE) and development kit (JDK) will be available for download and installation.

Reading over the features of Java 17, I become more convinced that the future of Java is to slowly and gradually absorb Scala features.

As you already know, Scala is a programming language for the Java Virtual Machine (JVM). The Scala compiler compiles Scala source to JVM bytecode just like the Java compiler.

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The most famous Java class is probably String. The second most famous is ArrayList<E>, from the java.util package. That class combines the speed and reliability of arrays with the sizing flexibility of linked lists.

There is no point in reinventing ArrayList<E>, other than that it is an excellent programming exercise. If you have the slightest concern that your knowledge of data structures might be lacking, reinventing an existing data structure sure helps shore up your knowledge, by giving you firsthand experience into what problems need to be solved.

Maybe you’ve done the array-backed set exercise. There are some similarities to…

Maybe you already know about how you can use the Tab key to complete partial typing on the Windows command prompt. Or maybe you don’t know this.

If you are a computer programmer who mostly uses Windows and you don’t already know about this, you need to read this article. And if you are a computer programmer who mostly uses Mac, maybe this feature is also available on all the shells you can use for the Mac Terminal.

I’ve been using the Windows command prompt for years, all the way back to a time when the Windows command prompt was…

One of the nice things about java.util.ArrayList is that you can iterate through the contents of a list with an “enhanced” For loop called the “For Each” loop. For example, given

ArrayList<Transaction> trx = account.getTransactions();

instead of having to write

CurrencyAmount bal = ZERO_DOLLARS;
for (i = 0; i < trx.size(); i++) {
    Transaction curr = trx.get(i);
    CurrencyAmount amt = curr.getAmount();
    bal = bal.plus(amt);
}

we can instead write

CurrencyAmount bal = ZERO_DOLLARS;
for (Transaction trs : trx) {
    CurrencyAmount amt = trs.getAmount();
    bal = bal.plus(amt);
}

Your integrated development environment (IDE) might suggest a lambda for even fewer lines.

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Reinventing existing data structures is an excellent computer programming exercise. Today, we’re going to make an array-backed mutable set in Java, using the test-driven development (TDD) methodology.

I expect you to follow along with your favorite integrated development environment (IDE) for Java, be it Eclipse, Apache NetBeans, IntelliJ IDEA or something else.

A set is like a list, but with two important differences: a set can’t contain duplicates, and order is irrelevant. Internally, the elements must be in some order, but that order should not matter to users (if order does matter, they should use a different data structure).

That…

Sometimes in a science fiction story, the extraterrestrials need to let us know that they’re intelligent life. What message can they send that we would understand? They might send the first few positive prime numbers.

Two blips. Pause. Three blips. Pause. Five blips. Pause. Seven blips, pause. Then 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, maybe send a few more besides those.

The prime numbers are good because the pattern is unlikely to be a random natural occurrence.

The extraterrestrials might include the number 1 in that list. They shouldn’t include 1 in that list, but…

Reinventing existing data structures is an excellent computer programming exercise. Today, we’re going to make a least recently used (LRU) cache in Java, using the test-driven development (TDD) methodology.

An LRU cache is essentially a fixed-capacity queue holding name-value pairs. When a name-value pair is added to the cache, it’s added at the front of the queue (or it’s added at the end and then immediately moved to the front).

The names are keys for retrieving the values. …