Java application notes

API docs

Java API documentation is maintained with Javadoc. To build the documentation, build LCM and then run the script:

$ lcm-java/make-javadocs.sh

Finding lcm.jar

The core LCM Java implementation is built to lcm.jar. To use LCM in your application, lcm.jar must be in your Java classpath.

On Linux, OS/X, and other UNIX-like systems, lcm.jar is typically built automatically and installed along with the rest of LCM. The exact location depends on the operating system and any configuration parameters, but it can often be found installed in /usr/local/share/java/.

Separately, lcm.jar can also be found in the lcm-java subdirectory of the source distribution after compiling LCM from source.

A lcm-sources.jar is also built and installed. This can provide IDE Javadoc integration.

LCM is currently not available on services like Maven Central. Your build system will need to be configured to point to a local jar.

Gradle project

An example of using LCM in a Gradle project. Assuming you have placed my-lcm-types.jar in ./lib:

// build.gradle
String osName = System.getProperty("os.name").toLowerCase();
project.logger.lifecycle(osName)
repositories { 
    mavenCentral()

    flatDir {
        if (osName.contains("linux")) {        
            dirs '/usr/local/share/java'
        } // else TODO
        dirs 'libs'
    }
}

dependencies {
    implementation ':lcm'
    implementation ':my-lcm-types'
}    

Note: flatDir is preferred over implementation files('/usr/local/share/java/lcm.jar'). Both work, but IDEs may not be able to find lcm-sources.jar with the files approach.

Eclipse project

See SO: How to import a jar in Eclipse? for an example of how to import a jar in Eclipse.

See SO: Attach the Source in Eclipse of a jar for instructions on how to attach a source jar in Eclipse (you might need to look at multiple answers).

InteliJ project

See SO: Correct way to add external jars (lib/*.jar) to an IntelliJ IDEA project for instructions on how to import a jar in IntelliJ.

Other

Use another build system like Ant or Maven? Please contribute instructions that work for you.

Namespace issues

LCM supports namespaces for data types, making it easier for users to use the types defined by others without worry that those types will conflict with other users’ types.

When defining a type, the name of the type can include a namespace, e.g., “struct examples.temperature_t { … }”. When compiled with lcm-gen, this will result in a class named “temperature_t” in package “examples”. If lcm-gen is given the root of a source tree with the –jpath flag, it will automatically put temperature_t.class in the examples subdirectory. You will need to remember to import that type before you use it, e.g., “import examples.*”, or else you will need to refer to types by their fully-qualified names (e.g., “new examples.temperature_t()”).

Note that if you do not specify a package name in your LCM type definition file, lcm-gen will (by default) put those types into the “lcmtypes” Java package. This is necessary because Java does not officially support packageless classes.