The key that allows Java to solve
both the security and the portability problems just described is that the
output of a Java compiler is not executable code. Rather, it is bytecode. Bytecode is a highly optimized set of
instructions designed to be executed by the Java run-time system, which is
called the Java Virtual
Machine (JVM). That
is, in its standard form, the JVM is an interpreter
for bytecode. This may come
as a bit of a surprise. As you know, C++ is compiled to executable code. In
fact, most modern languages are designed to be compiled, not interpreted—mostly
because of
performance concerns. However, the
fact that a Java program is executed by the
JVM helps solve the major problems
associated with downloading programs over
the Internet.
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