ajusted the markdown file

Author: PaddyKe

contents/stacks_and_queues/stacks_and_queues.md

@@ -18,12 +18,16 @@ Here is a simple implementation of a stack:
 {% method %}
 {% sample lang="ts" %}
 [import, lang:"typescript"](code/typescript/stack.ts)
+{% sample lang="java" %}
+[import, lang:"java"](code/java/Stack.java)
 {% endmethod %}
 
 Here is a simple implementation of a queue:
 {% method %}
 {% sample lang="ts" %}
 [import, lang:"typescript"](code/typescript/queue.ts)
+{% sample lang="java" %}
+[import, lang:"java" ](code/java/Queue.java)
 {% endmethod %}