Why is the operating system Android nescecary if the device is already running a Java virtual machine?

Question

1. Is the Android operating system written in Java?

2. Anything written in Java must run in a Java Virtual machine therefore if Android is written in Java it must itself be running in some sort of JVM, so is it?

3. According to the answers at this question a JVM doesn't need it's own operating system so why does Android exists and why doesn't Dalvik or someother JVM just run the apps itself?

Answer 1

This is basically covered by the Android Wikipedia page.

1. Android is written in layers. The main "OS" layer is based on the Linux kernel, which is written primarily in C. Some parts of what we think of as "the Android OS" (baked-in apps, some UI) are also written in Java.

2. The Java parts are run on something very like a JVM: Dalvik.

3. Because much of the software that makes up Android is not written in Java. Most Android apps are written in Java (although as Ted Hopp points out, the don't have to be). Anything that is written in Java (the Java parts of Android, and Java apps) is run in Dalvik.

Answer 2

1. According to Wikipedia, the core of Android is written in C, the UI is written in Java, and parts of it are written in C++. This is because Android is Linux, which was written in C.

2. The Java parts of Android do run in a JVM.

3. Android exists because Google's programmers created it. Dalvik does run the apps.

For more information, see Wikipedia's articles about Android and Dalvik.

Answer 3

1)Is the Android operating system written in Java?

No.

2)Anything written in Java must run in a Java Virtual machine therefore if Android is written in Java it must itself be running in some sort of JVM, so is it?

As it isn't written in Java the question's premiss is false.

3)According to the answers at this question a JVM doesn't need an operating system

The answers to that question don't say any such thing.

so why does Android exists and why doesn't Dalvik or someother JVM just run the apps itself?

Android is an operating system. Dalvik is a JVM.