Whay Android use java to build thier apps and IOS use objective-c ?

- Google decided to use Java because it was already being used to develop mobile applications on other platforms, notably, Sony Ericsson. Google figured that if it chose Java, developers could reuse their code and the play store would populate more quicklyy.

- iPhones run on iOS which is based off of Mac OS X. As OS X is natively written in C, C++ and Objective-C, apps for the plaform are developed in the same languages.

first we must know that:

- Java will get compiled to byte code that will be interpreted by a JVM ; NB:  since Android4.4, a new virtual machine appeared for Android called ART, it will get all bytecode compiled in assembly, but this is still experimental for now.

- Objective C will get compiled to assembly, that can be directly run by a processor

So, With Objective C you could argue that the language used to create apps is the same as the language to code the OS. For Android is would be more difficult to say so. The OS is build mostly in C, some parts in Java, but Android API them selves are also made of a mix of C and Java.