Java面向对象编程实例详解

我们要实现的Java应用程序是：当用户输入一个球体的半径，程序将显示该球体的体积与表面积。在您阅读下文以前，请您自己思考一分钟，您将如何设计该Java应用程序。

一、普通实现方法

我相信大多数程序员要实现上述功能的程序，非常迅速地、自信地将采用下面的实现代码：

class Sphere { public static void main(String[] args) { EasyReader console = new EasyReader(); System.out.print("Enter the radius: "); double radius = console.readDouble(); System.out.println("Radius = " + radius); double volume = 4.0 / 3.0 * Math.PI * radius * radius * radius; System.out.println("Volume = " + volume); double surfArea = 4.0 * Math.PI * radius * radius; System.out.println("Surface area = " + surfArea); } }

EasyReader类代码如下：

import java.io.*; public class EasyReader { protected String myFileName; protected BufferedReader myInFile; protected int myErrorFlags = 0; protected static final int OPENERROR = 0x0001; protected static final int CLOSEERROR = 0x0002; protected static final int READERROR = 0x0004; protected static final int EOF = 0x0100; /** * Constructor. Prepares console (System.in) for reading */ public EasyReader() { myFileName = null; myErrorFlags = 0; myInFile = new BufferedReader( new InputStreamReader(System.in), 128); } /** * Constructor. opens a file for reading * @param fileName the name or pathname of the file */ public EasyReader(String fileName) { myFileName = fileName; myErrorFlags = 0; try { myInFile = new BufferedReader(new FileReader(fileName), 1024); } catch (FileNotFoundException e) { myErrorFlags |= OPENERROR; myFileName = null; } } /** * Closes the file */ public void close() { if (myFileName == null) return; try { myInFile.close(); } catch (IOException e) { System.err.println("Error closing " + myFileName + " "); myErrorFlags |= CLOSEERROR; } } /** * Checks the status of the file * @return true if en error occurred opening or reading the file, * false otherwise */ public boolean bad() { return myErrorFlags != 0; } /** * Checks the EOF status of the file * @return true if EOF was encountered in the previous read * operation, false otherwise */ public boolean eof() { return (myErrorFlags & EOF) != 0; } private boolean ready() throws IOException { return myFileName == null || myInFile.ready(); } /** * Reads the next character from a file (any character including * a space or a newline character). * @return character read or <code>null</code> character * (Unicode 0) if trying to read beyond the EOF */ public char readChar() { char ch = 'u0000'; try { if (ready()) { ch = (char)myInFile.read(); } } catch (IOException e) { if (myFileName != null) System.err.println("Error reading " + myFileName + " "); myErrorFlags |= READERROR; } if (ch == 'u0000') myErrorFlags |= EOF; return ch; } /** * Reads from the current position in the file up to and including * the next newline character. The newline character is thrown away * @return the read string (excluding the newline character) or * null if trying to read beyond the EOF */ public String readLine() { String s = null; try { s = myInFile.readLine(); } catch (IOException e) { if (myFileName != null) System.err.println("Error reading " + myFileName + " "); myErrorFlags |= READERROR; } if (s == null) myErrorFlags |= EOF; return s; } /** * Skips whitespace and reads the next word (a string of consecutive * non-whitespace characters (up to but excluding the next space, * newline, etc.) * @return the read string or null if trying to read beyond the EOF */ public String readWord() { StringBuffer buffer = new StringBuffer(128); char ch = ' '; int count = 0; String s = null; try { while (ready() && Character.isWhitespace(ch)) ch = (char)myInFile.read(); while (ready() && !Character.isWhitespace(ch)) { count++; buffer.append(ch); myInFile.mark(1); ch = (char)myInFile.read(); }; if (count > 0) { myInFile.reset(); s = buffer.toString(); } else { myErrorFlags |= EOF; } } catch (IOException e) { if (myFileName != null) System.err.println("Error reading " + myFileName + " "); myErrorFlags |= READERROR; } return s; } /** * Reads the next integer (without validating its format) * @return the integer read or 0 if trying to read beyond the EOF */ public int readInt() { String s = readWord(); if (s != null) return Integer.parseInt(s); else return 0; } /** * Reads the next double (without validating its format) * @return the number read or 0 if trying to read beyond the EOF */ public double readDouble() { String s = readWord(); if (s != null) return Double.parseDouble(s); // in Java 1, use: return Double.valueOf(s).doubleValue(); else return 0.0; } }

以下是程序的输出结果画面。

在上述程序中，实现了球体表面积和体积的算法，并通过EasyReader类轻松实现了控制台的输入，但是该程序只是完成了程序所要求的功能，并计算出了结果。该程序不是一个好的设计程序，它既没采用结构化编程，也没有发挥Java语言的强大效能，更不是面向对象编程。

实际上，从程序设计的角度来看，以上程序是一个非常糟糕的设计程序。首先，用户界面与计算公式混合在一起。请记住：对于任何编程语言，用户界面必须与计算或处理过程分离开来。另外，输出的结果太难看，数值包括太多的小数。