Apple must write a Java interpreter for their new system.
Apple writes a Java interpreter for their new system. Now that one program (the interpreter) can run on their system, and that interpreter can run any Java bytecode program. Nothing new needs to be done with those bytecode programs.
Java programs are portable, which means that the same bytecode program can run on any computer system that has a Java interpreter. Also, a source program can be compiled into bytecodes on any computer that has a Java compiler.
The source program does not have to be changed to meet the particular needs of a particular computer systems. No matter what computer you have, you can write the same Java programs.
This is unlike most older programming languages, where a different version of a program must be made for each variety of computer, and an executable program that runs on one type of computer will not run on another.
Since Java was created (in 1995) several newer languages have also embraced the idea of portability. Notable among these are JavaScript, Python, and PHP. Your web browser contains a JavaScript interpreter and can run JavaScript source code embedded in a web page, regardless of where the page is hosted. (JavaScript is not Java. Its name is intended to draw attention to its Java-like portability.)
Can bytecodes be sent from computer to computer over the Internet?