We are now well into the new six-month release cadence of the JDK and, with the release of JDK 13, it is clearly working well.

One thing that is obvious is that, whilst the overall rate of change for the Java platform has increased, individual releases will have fewer new features. This is the case with JDK 13, which includes only five JDK Enhancement Proposals (JEPs) and 76 new core library elements (of which nearly half are simple additions to the java.io package).

This is a preview of the Java 13 Refcard. To read the entire Refcard, please download the PDF from the link above.

Let's start with a change to the language syntax, in the form of text blocks (JEP 355). Java has always suffered a little from the way strings are defined. A string starts with a double-quote and ends with a double-quote, which is fine, except that the string cannot span more than one line. This leads to workarounds, like including \n where line breaks are required or concatenating strings and newlines, but these do not lend themselves to clear code. In JDK 12, there was a proposal for raw-string literals (JEP 326), but the feedback from the early access builds of the JDK was such that the decision was made to remove it before release.

Text blocks are a different solution to the same challenge. A text block starts with a triple double-quote and is terminated with the same. Anything between them is interpreted as a part of the string, including new lines. There is nothing magical about the end result, which is still a normal java.lang.String object. Text blocks can be used anywhere that a string literal can be used in Java with no difference to the compiled code.

This is a preview of the Java 13 Refcard. To read the entire Refcard, please download the PDF from the link above.

There is another (small) language change in JDK 13, covered by JEP 354. This applies to the switch expression feature that was included in JDK 12 as the first-ever preview feature. Here, we have a perfect example of why preview features are an excellent idea.

Until JDK 12, a switch could only be used as a statement, where it performed an action but did not return a result. In JDK 12, a switch can now be used as an expression, meaning it returns a result that can be assigned to a variable. There were also several changes to the syntax of case statements within the switch expressions. Let's use the example from the JEP to understand how this works.

This is a preview of the Java 13 Refcard. To read the entire Refcard, please download the PDF from the link above.

JDK 13 also includes three JEPs that relate to the virtual machine.

• JEP 350: Dynamic CDS Archive. This is an extension to the application class data sharing functionality (AppCDS) that was contributed by Oracle to OpenJDK 10. Prior to that, it was included in the Oracle JDK as a commercial feature. This extension allows the dynamic archiving of classes at the end of the execution of a Java application. The archived classes include all loaded application classes and library classes that are not present in the default, base-layer CDS archive. This also eliminates the need to perform a training run of an application. Using AppCDS prior to this was a multi-step process involving the creation of a list of relevant classes and using this list to generate the archive to be used for subsequent runs. Now, all that is required is a single run of an application with the -XX:ArchiveClassesAtExit flag providing the location where the archive will be written.

This is a preview of the Java 13 Refcard. To read the entire Refcard, please download the PDF from the link above

As mentioned previously, JDK 13 includes only 76 new APIs in the core class libraries. These cover the following areas:

• Updates to Unicode support.
• Three new methods in String to support text blocks already described.
• The type-specific Buffer classes of java.nio now have absolute (as opposed to relative) bulk get and set methods. They, as well as the base abstract Buffer class, include a slice() method to extract part of the buffer.
• MappedByteBuffer has a force() method that will force a write of a section of the buffer to its backing store.
• java.nio.FileSystem adds three new overloaded forms of  newFileSystem() to access the contents of a file as a file system.
• There's an interesting new method in  javax.annotation.processing.ProcessingEnvironment --- isPreviewEnabled(). This will tell you whether the preview features (discussed earlier) are enabled. The reason this is interesting is that the annotation, @PreviewFeature, will not be available until JDK 14.
• Element-specific types in javax.lang.model.element all get the asType() method. This returns a pseudo-type.
•  DocumentBuilderFactory and  SAXParserFactory in  javax.xml.parsers get three new methods to create namespace-aware instances.

This is a preview of the Java 13 Refcard. To read the entire Refcard, please download the PDF from the link above

As you can see, JDK 13 does not have a large number of new features and APIs. However, it continues to deliver the incremental evolution of Java, ensuring it remains the most popular programming language on the planet.

This is a preview of the Java 13 Refcard. To read the entire Refcard, please download the PDF from the link above.