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Good day house!
Can someone please explain what regular expressions are in java and how they are being used. Thank you

Following. Regex have always left me in a twist l

Op, what textbook are u using?

asalimpo:
Op, what textbook are u using?

Java how to program by deitel and deitel 10th edition. Thank you

clockwisereport:
Java how to program by deitel and deitel 10th edition. Thank you

Regular expressions are mini languages within programming languages whose domain are strings. So regex is for describing string patterns. It has a syntax (varies according by language). The issue is in learning the syntax. I found it weird when I was starting out, but now it ain't so intimidating, just off-putting . My advice is don't bother with it,if you don't have to. When you are more mature and grounded in programming you give it a try. I wrote/still write all string manipulation functions by hand and have never used regex. Though I write code in d thousands of lines. But if you wanna still grok it,ditch deitel. Their books are glossy but crap. And they don't explain regular expressions well at al. Get a dedicated resource on by regex then study from there. The diffs btw typical regex and typical programming languages are that usually, you can't create variables. You can't do explicit iteration: looping.
If you use Windows command line, you probably use some form of regex. E.g to find all Java files in a directory,you'd enter dir *.java . The * is short for match 0 to inf characters. They are actually 2 bits or components to that pattern . 1)* 2) .java . So the engine that processes regexes will match for the two, component by component. If you weren't using regex but rather using explicit string methods,you'd call endsWith() . Still same thing.

It’s used to compare and match strings. It’s like having a circular hole and seeing if a circle will fit or if a square will fit.

For instance in scala/pseudocode I can say:
Val regex = ([0-9]).r
Val number = 6
println(number.matches(regex)) //true

Thanks @Asalimpo and @Olafisoyem.. I appreciate your efforts