Why is Java known as a platform neutral language?

Answer 1

The compiler generates a pseudocode, not targeted to any machine, called bytecode. This can be interpreted by an interpreter program or hardware accelerator on any computer. Java is not the only language that can be compiled to bytecode. For example the GCC compiler system has a backend that emits bytecode, and has already been integrated with the Ada language frontend (and maybe others).

Java is NOT the first language to be implemented platform neutral. In the 1970s UCSD developed a platform neutral Pascal compiler that generated a pseudocode, not targeted to any machine, called P-code. This allowed all computers on campus to run the same operating system, compiler, and programs. All that was needed was a native P-code interpreter program. Apple Pascal on the Apple ][ used this system too, with only minor changes from the original UCSD system so that it ran on Apple's DOS. The UCSD product was available on most computers of the era, but mismanaged costs and the performance penalty of the interpreter program eventually killed it in the middle/late 1980s.