Under the Hood

Under the Hood

Java security: How to install the security manager and customize your security policy
One of the primary reasons Java technology is a "good fit" for networks is that it has a comprehensive security model designed into its architecture. This article turns to one aspect of that security model: the security manager of the Java virtual machine (JVM). The security manager, working in concert with the Java API, enables programmers to establish a custom security policy for their Java applications. (2,600 words)
Bill Venners, November 1997

Security and the class verifier
One of the primary reasons Java technology is a "good fit" for networks is that it has a comprehensive security model designed into its architecture. This article turns to one aspect of that security model: the class verifier of the Java virtual machine (JVM). The class verifier enables untrusted code to be verified up front, rather than on the fly as the code is executed. This ability provides uninterrupted execution (the program can't "crash" uncontrollably) at a minimal cost in speed degradation. (3,800 words)
Bill Venners, October 1997

Security and the class loader architecture
One of the primary reasons Java technology is a "good fit" for networks is that it has a comprehensive security model designed into its architecture. Beginning with a refresher on the Java sandbox, this article turns to one aspect of that security model: the class loader architecture of the Java virtual machine. The class loader architecture causes code downloaded from different sources to be kept separate, and prevents the loading of untrusted classes that declare themselves to be part of a trusted library. (3,000 words)
Bill Venners, September 1997

How the Java virtual machine performs thread synchronization
The last article in an <strong>Under the Hood</strong> series on Java bytecode, this article by Bill Venners covers threads, shared data, locks, and more!
Bill Venners, July 1997

How the Java virtual machine handles method invocation and return
This article takes a look at how method invocation and return is handled by the Java virtual machine, with a close inspection of the relevant bytecodes is included. The article ends with a source-code example of method invocation. (2,500 words)
Bill Venners, June 1997

Solve real problems with aglets, a type of mobile agent
Mobile agents have been around for many years, but they haven't yet entered the mainstream. Last month's Under The Hood described the inner workings of aglets, a mobile-agent technology built on top of Java. This article answers the question, Why would developers choose mobile agents over other software technologies, such as client/server, applets, and servlets, for solving real-world problems? (2,900 words)
Bill Venners, May 1997

How the Java virtual machine handles exceptions
All Java programs are compiled into class files that contain bytecodes, the machine language of the Java virtual machine. This article takes a look at the way exceptions are handled by the Java virtual machine, including the exception table and the bytecodes related to exceptions. (2,000 words)
Bill Venners, January 1997

Objects and arrays
All Java programs are compiled into class files that contain bytecodes, the machine language of the Java virtual machine. This article takes a look at the bytecodes that manipulate objects and arrays. (2,500 words)
Bill Venners, December 1996

Floating-point arithmetic
All Java programs are compiled into class files which contain bytecodes, the machine language of the Java virtual machine. This article takes a look at the bytecodes that implement the floating-point capabilities of Java. (2,500 words)
Bill Venners, October 1996

Bytecode basics
All Java programs are compiled into class files that contain bytecodes, the machine language of the Java virtual machine. Here's a first look at Java's bytecodes. (3,500 words)
Bill Venners, September 1996

The Java class file lifestyle
A key component of Java is the Java class file -- a precisely defined file format to which Java programs are compiled. The class file can be loaded by any Java Virtual Machine implementation and is the vehicle for the transmission of compiled Java across networks. Here's a hands-on introduction to the Java class file. (1,500 words)
Bill Venners, July 1996

The lean, mean, virtual machine
A key component of Java is the Java Virtual Machine -- a virtual computer, typically implemented in software on top of a "real" hardware platform and operating system, that runs compiled Java programs. Thanks to the JVM, programs written in Java don't have to be rewritten to run on different computers. Here's a hands-on introduction to the JVM.
Bill Venners, June 1996