Merge pull request #13145 from edizor/master

Update README

core-java-modules/core-java-collections-4/README.md

@@ -12,3 +12,5 @@
 - [Fixed Size Queue Implementations in Java](https://www.baeldung.com/java-fixed-size-queue)
 - [Difference Between Java Enumeration and Iterator](https://www.baeldung.com/java-enumeration-vs-iterator)
 - [Sort Collection of Objects by Multiple Fields in Java](https://www.baeldung.com/java-sort-collection-multiple-fields)
+- [Guide to Java PriorityQueue](https://www.baeldung.com/java-priorityqueue)
+- [Java Generics PECS – Producer Extends Consumer Super](https://www.baeldung.com/java-generics-pecs)

core-java-modules/core-java-string-operations-5/README.md

@@ -6,3 +6,4 @@
 - [Capitalize the First Letter of a String in Java](https://www.baeldung.com/java-string-uppercase-first-letter)
 - [Convert String to char in Java](https://www.baeldung.com/java-convert-string-to-char)
 - [Convert String to String Array](https://www.baeldung.com/java-convert-string-to-string-array)
+- [String Interpolation in Java](https://www.baeldung.com/java-string-interpolation)

gcp-firebase/README.md

@@ -0,0 +1,3 @@
+## Relevant Articles
+
+- [Using Firebase Cloud Messaging in Spring Boot Applications](https://www.baeldung.com/spring-fcm)

spring-boot-modules/spring-boot-graphql/README.md

@@ -12,6 +12,7 @@ The "REST With Spring" Classes: http://bit.ly/restwithspring
 - [Error Handling in GraphQL With Spring Boot](https://www.baeldung.com/spring-graphql-error-handling)
 - [How to Test GraphQL Using Postman](https://www.baeldung.com/graphql-postman)
 - [GraphQL vs REST](https://www.baeldung.com/graphql-vs-rest)
+- [REST vs. GraphQL vs. gRPC – Which API to Choose?](https://www.baeldung.com/rest-vs-graphql-vs-grpc)
 
 ### GraphQL sample queries
 

spring-boot-modules/spring-boot-process-automation/README.md

@@ -0,0 +1,3 @@
+## Relevant Articles
+
+- [Running Spring Boot Applications with the Embedded Camunda Engine](https://www.baeldung.com/spring-boot-embedded-camunda)

spring-core-6/README.md

@@ -2,3 +2,4 @@
 ### Relevant Articles:
 - [Instantiating Multiple Beans of the Same Class with Spring Annotations](https://www.baeldung.com/spring-same-class-multiple-beans)
 - [Using Environment Variables in Spring Boot’s application.properties](https://www.baeldung.com/spring-boot-properties-env-variables)
+- [Reinitialize Singleton Bean in Spring Context](https://www.baeldung.com/spring-reinitialize-singleton-bean)

spring-credhub/README.md

@@ -0,0 +1,3 @@
+## Relevant Articles
+
+- [A Guide to Spring CredHub](https://www.baeldung.com/spring-credhub)