java example

http://www.java2s.com/

http://beginnersbook.com/java-tutorial-for-beginners-with-examples/

https://www.tutorialspoint.com/java/index.htm

https://www.javatpoint.com/java-tutorial

5 Difference Between HashMap And WeakHashMap In Java With Example

http://javahungry.blogspot.com/2015/09/difference-between-weakhashmap-and-hashmap-with-exmaple.html

WeakHashMap ใน java

http://na5cent.blogspot.com/2014/09/weakhashmap-java.html