java: add classpath example and update link (#7358)

pages/common/java.md

@@ -1,12 +1,16 @@
 # java
 
 > Java Application Launcher.
-> More information: <https://java.com>.
+> More information: <https://docs.oracle.com/en/java/javase/17/docs/specs/man/java.html>.
 
 - Execute a java `.class` file that contains a main method by using just the class name:
 
 `java {{classname}}`
 
+- Execute a java program and use additional third-party or user-defined classes:
+
+`java -classpath {{path/to/classes1}}:{{path/to/classes2}}:. {{classname}}`
+
 - Execute a `.jar` program:
 
 `java -jar {{filename.jar}}`