Examples are provided in directory examples/java of the source distribution of GLPK for Java.
To compile the examples the classpath must point to glpk-java.jar, e.g.
javac -classpath /usr/local/shared/java/glpk-java.jar Example.java
To run the examples the classpath must point to glpk-java.jar. The java.library.path must point to the directory with the dynamic link libraries, e.g.
java -Djava.library.path=/usr/local/lib/jni \ -classpath /usr/local/shared/java/glpk-java.jar:. \ Example