The Java Language Environment

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6.1 Memory Allocation and Layout

One of the Java compiler's primary lines of defense is its memory allocation and reference model. First of all, memory layout decisions are not made by the Java language compiler, as they are in C and C++. Rather, memory layout is deferred to run time, and will potentially differ depending on the characteristics of the hardware and software platforms on which the Java system executes.

Secondly, Java does not have "pointers" in the traditional C and C++ sense of memory cells that contain the addresses of other memory cells.The Java compiled code references memory via symbolic "handles" that are resolved to real memory addresses at run time by the Java interpreter. Java programmers can't forge pointers to memory, because the memory allocation and referencing model is completely opaque to the programmer and controlled entirely by the underlying run-time platform.

Very late binding of structures to memory means that programmers can't infer the physical memory layout of a class by looking at its declaration. By removing the C and C++ memory layout and pointer models, the Java language has eliminated the programmer's ability to get behind the scenes and either forge or otherwise manufacture pointers to memory. These features must be viewed as positive benefits rather than a restriction on the programmer, because they ultimately lead to more reliable and secure applications.

Copyright © 1997 Sun Microsystems, Inc. All Rights Reserved.
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