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How does Apache Pig handle nulls

It is important to understand that in Pig the concept of null is the same as in SQL, which is completely different from the concept of null…

Oct 14

Find ubuntu environment variables

We know that echo $PATH will print all of the environment variables. There are several places we can put the path variables in.

Oct 13

Spring Beans scope: Singleton and Prototype

Oct 11

Spring Autowire beans that have the same type

With spring annotation @Autowired annotation, we can bind the bean automatically by type.

Oct 9

Store Scrapy crawled data in PostgresSQL

Store Scrapy crawled data in PostgresSQL

Prerequisites: Assume that you are able to craw some data following the tutorial provided by Scrapy official website until the step…

Sep 24

Overriding hashCode method — Effective Java Notes

When overriding the equalmethod, always override the hashCode()method, or the HashSet, HashMap... methods would fail.

Aug 1

5 Rules for overriding equal method — Effective Java Notes

When we create a new class, most time we need to override the equal method. The book lists 5 rules.

Jul 26

3 Methods to Create Singleton with Java — Effective Java Notes

I only know one singleton creation method before, the factory method. The book list three methods and suggusts that the third method-Enum…

Jul 25

AWK example

AWK is the abbreviation of three developers’ names.

Jul 24

Consider builder when facing with many constructor -Effective Java Notes

When to use? we have many parameters in a class.

Jul 23

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