Java是一种面向对象的语言，是实现面向对象编程的强大工具。但如何在编程中实际运用并发挥其最大效能呢？本文通过一个实际Java程序的开发过程，详细说明了如何使用面向对象实现Java编程。

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 null 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。