【正文】 one of the most powerful concepts in OOP. An object has an interface Aristotle was probably the first to begin a careful study of the concept of type。大連交通大學(xué) 2020 屆本科生畢業(yè)設(shè)計(jì)（論文）外文翻譯 1 The progress of Abstraction All programming languages provide abstractions. It can be argued that the plexity of the problems you’re able to solve is directly related to the kind and quality of abstraction. By “kind” I mean, “What is it that you are abstracting?” Assembly language is a small abstraction of the underlying machine. Many socalled “imperative” languages that followed (such as Fortran, BASIC, and C) were abstractions of assembly languages are big improvements over assembly language, but their primary abstraction still requires you to think in terms of the structure of the puter rather than the structure of the problem you are trying to solve. The programmer must establish the association between the machine model (in the “solution space,” which is the place where you’re modeling that problem, such as a puter) and the model of the problem that is actually being solved (in the “problem space,” which is the place where the problem exists). The effort required to perform this mapping, and the fact that it is extrinsic to the programming language, produces programs that are difficult to write and expensive to maintain, and as a side effect created the entire “programming methods” alternative to modeling the machine is to model the problem you’re trying to solve. Early languages such as LISP and APL chose particular views of the world (“All problems are ultimately lists” or “All problems are algorithmic,” respectively). PROLOG casts all problems into chains of decisions. Languages have been created for constraintbasedprogramming and for programming exclusively by manipulating graphical symbols. (The latter proved to be too restrictive.) Each of these approaches is a good solution to the particular class of problem they’re designed to solve, but when you step outside of that domain they bee awkward. The objectoriented approach goes a step further by providing tools for the programmer to represent elements in the problem is general enough that the programmer is not constrained to any particular type of problem. We refer to the elements in the problem space and their representations in the solution space as “objects.” (Of course, you will also need other objects that don’t have problemspace analogs.) The idea is that the program is allowed to adapt itself to the lingo of the 大連交通大學(xué) 2020 屆本科生畢業(yè)設(shè)計(jì)（論文）外文翻譯 2 problem by adding new types of objects, so when you read the code describing the solution, you’re reading words that also express the problem. This is a more flexible and powerful language abstraction than what we’ve had before. Thus, OOP allows you to describe the problem in terms of the problem, rather than in terms of the puter where the solution will run. There’s still a connection back to the puter, though. Each object looks quite a bit like a little puter。 it has a state, and it has operations that you can ask it to perform. However, this doesn’t seem like such a bad analogy to objects in the real world—they all have characteristics and behaviors. Some language designers have decided that objectoriented programming by itself is not adequate to easily solve all programming problems, and advocate the bination of various approaches into multiparadigm programming languages. Alan Kay summarized five basic characteristics of Smalltalk, the first successful objectoriented language and one of the languages upon which Java is based. These characteristics represent a pure approach to objectoriented programming: 1. Everything is an object. Think of an object as a fancy variable。 he spoke of “the class of fishes and the class of birds.” The idea that all objects, while being unique, are also part of a class of objects that have characteristics and behaviors in mon was used directly in the first objectoriented language, Simula67, with its fundamental keyword class that introduces a new type into a program. Simula, as its name implies, was created for developing simula