java - What is the difference between .class and .dex files?

Question

Of course, .dex files are for the Dalvik VM of Android and .class files are for the JVM. But I wonder if they have similar layouts (Constant Pool, Fields, Methods, Attributes, ...)? The bytecode is different, but are there Dalvik specific opcode equivalents to the ones from the JVM?

Answer 1

Whereas a Java jar file has many class files, each APK file has only a single classes.dex file, as shown below. According to Google, the APK format differs from the class-file format for performance and security reasons.