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README.md

Chapter 18 - Future Java

Ch18/ch18

This directory contains multiple examples. It may be loaded in IDE at the Ch18 level. Java 18+ is required.

  • ch18/AmberExamples.java - Demonstrating further pattern matching from Project Amber
  • ch18/Java17Examples.java - Demonstrating various new features of Java 17
  • ch18/SwitchExamples.java - Switch expression examples

Alternatively, the samples may be compiled and run at the command-line as follows:

cd Ch18/ch18
javac *.java
java -cp .. ch18.SwitchExamples

`Ch18/Panama

This is one of the more complex examples in the book given it's use of native libraries and the EA state of Panama.

This has been tested using an EA Panama build of JDK 17 (build 17-panama+3-167 (2022/1/18)) from https://jdk.java.net/panama/17/ and 0.7.2 of libspng

libspng installation

The project requires the native library libspng be installed. While this may be installable with your package manager of choice, we recommend cloning from GitHub and building locally to ensure everything lines up.

To clone the library and move to the expected version:

cd Ch18/Panama
git clone [email protected]:randy408/libspng.git
cd libspng
git checkout v0.7.2

Note that newer versions may differ from the generated wrappers, so if you don't use v0.7.2 then you'll need to run jextract rather than using the checked in wrappers.

To build the library:

cd Ch18/Panama/libspng

mkdir cbuild
cd cbuild
cmake ..
make

We don't bother to make install to a system location as we'll use the library directly where the build generated.

This may require installing cmake through your package manager if it is not already available. Further instructions, options at are available at https://github.com/randy408/libspng/blob/v0.7.2/docs/build.md:

jextract generating wrappers

To generate the wrapper classes, you'll need the Panama EA (https://jdk.java.net/panama/) to get access to the jextract tool.

To run the extraction where this project expects it, do the following:

cd Ch18/Panama/src/main/java

jextract --source -t org.libspng \
  -I /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include \
  -l spng ../../../libspng/spng/spng.h

The -I for including system types may need to be altered to match your OS's location for typical native headers.

Depending on your path settings, jextract may not be directly available to your shell. If that's the case, you can run it with $JAVA_HOME/bin/jextract when you're using the Panama EA JDK version.

Building and running the app

Building the project requires JDK 17+ (only jextract requires the Panama EA).

From the Ch18/Panama project root:

cd Ch18/Panama

./gradlew jar

java -Djava.library.path=./libspng/cbuild \
   --add-modules=jdk.incubator.foreign \
   --enable-native-access=ALL-UNNAMED \
    -jar build/libs/Panama.jar \
   ./libspng/tests/images/basi0g01.png

When run against a png file, you should see output indicating what type of image it is.

WARNING: Using incubator modules: jdk.incubator.foreign
File type: grayscale