Certificate encodings with X509Certificates and keytool

I am looking into X509Certificates and keytool and I am confused on the following:

A c开发者_C百科ertificate can be stored in cer (Canonical Encoding Rules) format as well as in DER?

I am reviewing various tutorials by SUN on keytool and in some cases they seem to import a certificate ending in ".cer" or exporting one with the extension ".cer".

E.g.

keytool -importcert -alias abc -file ABCCA.cer  OR  
keytool -exportcert -alias mykey -file MJ.cer

Does this mean cer encoding?Because initially I had the impresion that if you do an export on keytool the default is der.

Or is cer and der interchangeable?

Thanks

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By default, keytool exports using DER ("Distinguished Encoding Rules"), a common binary encoding for X509 certificates.

It's just an unfortunate coincidence that CER is the name of another ASN.1 encoding, as well as being the first three letters of "certificate"...