Add chapters 18-20 for the java book

Java-Kompendium/kap19/2/build.gradle

@@ -0,0 +1,19 @@
+plugins {
+    id 'application'
+}
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    implementation 'com.googlecode.json-simple:json-simple:1.1.1'
+}
+
+run {
+    standardInput = System.in
+}
+
+application {
+    mainClass = 'Main'
+}