97 Things Every Java Programmer Should Know

Chapter 40. Java Is a ’90s Kid

Ben Evans

There are only two kinds of languages: the ones people complain about and the ones nobody uses.

Bjarne Stroustrup

Whether Stroustrup’s insight says more about programming languages or human nature, I’m not sure. However, it does draw attention to the often-forgotten truism that the design of programming languages is a human endeavor. As such, languages always carry traces of the environment and context in which they were created.

So it shouldn’t come as a surprise that traces of the late 1990s can be seen everywhere in the design of Java, if you know where to look.

For example, the sequence of bytes to load an object reference from local variable 0 onto the temporary evaluation stack is this two-byte sequence:

19 00 // aload 00

However, the JVM’s bytecode instruction set provides a variant form that is one byte shorter:

2A // aload_0

One byte saved may not sound like much, but it can start to add up over an entire class file.

Now, remember, in the late ’90s, Java classes (often applets) were downloaded over dial-up modems, incredible devices that were capable of reaching blistering speeds of 14.4 kilobits per second. With that kind of bandwidth, saving bytes wherever possible was a huge motivation for Java.

You could even argue that the entire concept of primitive types is a combination of a performance hack and a sop to C++ programmers ...