Add chapters 18-20 for the java book

Java-Kompendium/kap20/2/gradle/libs.versions.toml

@@ -0,0 +1,10 @@
+# This file was generated by the Gradle 'init' task.
+# https://docs.gradle.org/current/userguide/platforms.html#sub::toml-dependencies-format
+
+[versions]
+guava = "33.4.6-jre"
+junit = "4.13.2"
+
+[libraries]
+guava = { module = "com.google.guava:guava", version.ref = "guava" }
+junit = { module = "junit:junit", version.ref = "junit" }