Open APK File

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JAR File

JAR file stands for Java Archive. JAR file typically used to store multiple Java classes and related resources and metadata. Also JAR files may contain add-ons or themes for Mozilla Firefox or Thunderbird E-Mail Client. APK is a variation of JAR files used to distribute Android applications.

JAR files are ZIP compressed archives. Inside each JAR file contains Java classes, associated resources and manifest file which describes what is inside JAR file and how it should be handled. Manifest file in JAR file is called MANIFEST.MF and is located in META-INF folder. For specific information on how manifest file should look like could be found on Java reference website. Below is an example of MANIFEST.MF file which contains definitions of BigDecimal.class and BigInteger.class classes and their corresponding digests:

Manifest-Version: 1.0

Name: java/math/BigDecimal.class
SHA1-Digest: TD1GZt8G11dXY2p4olSZPc5Rj64=
MD5-Digest: z6z8xPj2AW/Q9AkRSPF0cg==

Name: java/math/BigInteger.class
SHA1-Digest: oBmrvIkBnSxdNZzPh5iLyF0S+bE=
MD5-Digest: wFymhDKjNreNZ4AzDWWg1Q==

JAR files provide an efficient way to distribute application and dependencies to the execution environment. Also with JAR file it is possible to verify consistency of the distribution to make sure that application was not modified during copying process.