What is the difference between UNION and UNION ALL?

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This deals with SQL. UNION only selects distinct values, UNION ALL selects all values. In the context of Core Java, the terms UNION and UNION ALL are not directly related. Instead, they are typically associated with SQL (Structured Query Language), which is used for database operations. In SQL: UNION: The UNION operator is used to combine … Read more

What is a Left outer join?

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This deals with SQL. Left outer join preserves the unmatched rows from the first (left) table, joining them with a NULL row in the shape of the second (right) table. In the context of Core Java, it’s important to note that Java itself is a programming language and does not directly deal with SQL or database … Read more

What is the difference between JAR and WAR files?

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JAR files (Java ARchive) allows aggregating many files into one, it is usually used to hold Java classes in a library. WAR files (Web Application aRchive) stores XML, java classes, and JavaServer pages for Web Application purposes. In Java, JAR (Java Archive) and WAR (Web Application Archive) files are both archive file formats, but they … Read more

How does the version control process works?

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Initiate, pull, branch, merge, commit, push. (Init) Make your own repository. (Pull) Download an existing repository from a url. (Branch / Merge )Make revisions. Commit then push your modifications. It seems like there might be a misunderstanding in your question. The question is related to Core Java, but the topic you’re asking about, the version … Read more

How does a 3 tier application differ from a 2 tier one?

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Tiers are the physical units of separation or deployment, while layers are the logical units of separation. Imagine that you’re designing an e-commerce website. A 3 tier architecture would consist of web pages, a web server and a database, with the corresponding 3 layers being the “Presentation”, “Business Logic” and “Database” layers. If you take … Read more