Electrical computers and digital processing systems: multicomput – Computer-to-computer data routing – Least weight routing
Reexamination Certificate
1999-05-28
2003-04-29
Courtenay, III, St. John (Department: 2126)
Electrical computers and digital processing systems: multicomput
Computer-to-computer data routing
Least weight routing
C709S241000, C717S116000, C717S118000
Reexamination Certificate
active
06557023
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates computer programs and, more specifically, to minimizing internal structures at program runtime.
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2. Background Art
Computer systems comprise resources that are used to execute computer programs such as memory and processor (or processing) time. A computer program's code (or instruction set) is typically copied into the computer systems memory, or other storage, before it is executed thereby using processor time. In addition to the computer program's code, the computer system's storage may also be used to retain information about the state of the computer program during execution. This information adds additional overhead to the execution as it is necessary to allocate memory to store the information and to use other resources such as processor time to manage the information.
One example of program information that is stored during program execution are symbol, field and method tables. These tables are examples of internal structures that use space in memory during program execution. Further, processor time is used to maintain the information contained in the internal structures. It would be beneficial to be able to reduce the internal structures that are used during execution thereby reducing memory and processor time during program execution.
The problems associated with the use of internal structures during program execution can be better understood from a review of a virtual machine's processing environment and an overview of object-oriented programming.
Object-Oriented Programming
Object-oriented programming is a method of creating computer programs by combining certain fundamental building blocks, and creating relationships among and between the building blocks. The building blocks in object-oriented programming systems are called “objects.” A software application can be written using an object-oriented programming language whereby the program's functionality is implemented using these objects.
An object is a programming unit that groups together a data structure (one or more instance variables) and the operations (methods) that can use or affect that data. Thus, an object consists of data and one or more operations or procedures that can be performed on that data. The joining of data and operations into a unitary building block is called “encapsulation.”
An object can be instructed to perform one of its methods when it receives a “message.” A message is a command or instruction sent to the object to execute a certain method. A message consists of a method selection (e.g., method name) and a plurality of arguments. A message tells the receiving object what operations to perform.
One advantage of object-oriented programming is the way in which methods are invoked. When a message is sent to an object, it is not necessary for the message to instruct the object how to perform a certain method. It is only necessary to request that the object execute the method. This greatly simplifies program development.
Object-oriented programming languages are predominantly based on a “class” scheme. The class-based object-oriented programming scheme is generally described in Lieberman, “Using Prototypical Objects to Implement Shared Behavior in Object-Oriented Systems,” OOPSLA 86 Proceedings, September 1986, pp. 214-223.
An object class provides a definition for an object which typically includes both variables and methods. An object class is used to create a particular object “instance.” (The term “object” by itself is often used interchangeably to refer to a particular class or a particular instance.) An instance of an object class includes the variables and methods defined for the class. Multiple instances can be created from the same object class. Each instance that is created from the object class is said to be of the same type or class.
To illustrate, an employee object class can include “name” and “salary” instance variables and a “set_salary” method. Instances of the employee object class can be created, or instantiated for each employee in an organization. Each object instance is said to be of type “employee.” Each employee object instance includes “name” and “salary” instance variables and the “set_salary” method. The values associated with the “name” and “salary” variables in each employee object instance contain the name and salary of an employee in the organization. A message can be sent to an employee's employee object instance to invoke the “set_salary” method to modify the employee's salary (i.e., the value associated with the “salary” variable in the employee's employee object).
A hierarchy of classes can be defined such that an object class definition has one or more subclasses. A subclass inherits its parent's (and grandparent's etc.) definition. Each subclass in the hierarchy may add to or modify the behavior specified by its parent class. Some object-oriented programming languages support multiple inheritance where a subclass may inherit a class definition from more than one parent class. Other programming languages support only single inheritance, where a subclass is limited to inheriting the class definition of only one parent class. The Java programming language also provides a mechanism known as an “interface” which comprises a set of constant and abstract method declarations. An object class can implement the abstract methods defined in an interface. Both single and multiple inheritance are available to an interface. That is, an interface can inherit an interface definition from more than one parent interface.
Platform-Independent Programming Languages and Program Execution
Object-oriented software applications (e.g., applications written using the Java programming language) typically comprise one or more object classes and interfaces. Many programming languages can be used to write a program which is compiled into machine-dependent (or platform-dependent), executable code. However, in other languages such as the Java programming language, program code (e.g., classes) may be compiled into platform-independent bytecode class files. Each class contains code and data in a platform-independent format. A bytecode includes a code that identifies an instruction (an opcode) and none or more operands to be used in executing the instruction. The computer system acting as the execution vehicle contains a program such as a virtual machine, which is responsible for executing the platform-independent code (e.g., bytecodes generated from a program written using the Java programming language).
Platform-independent programs have an advantage of being usable on multiple platforms. There is no need to develop program code for multiple platforms. The same platform-independent program can be executed on multiple platforms using a virtual machine or other mechanism that is configured to translate the platform-independent code into platform-dependent code. Thus, an application developer can develop one version of an application's program code that can ultimately be executed on multiple platforms, for example.
Applications may be designed as standalone applications, or as “applets” which are identified by an applet tag in an HTML (Hypertext Markup Language) document, an
Courtenay III St. John
Gunnison McKay & Hodgson, L.L.P.
McKay Philip J.
Sun Microsystems Inc.
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