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Core Java -- Class Design Hints

Benjamine — Fri, 10 Dec 2010 05:41:00 GMT

1. Always keep data private.

2. Always initialize data.

3. Don't use too many basic types in a class.

4. Not all fields need individual field accessors and mutators.

5. Use a standard form for class definitions.

6. Break up classes with too many responsibilities.

7. Make the names of your classes and methods reflect their responsibilities.

Benjamine 2010-12-10 13:41 发表评论

Core Java学习�W�记(�?

Benjamine — Fri, 10 Dec 2010 04:00:00 GMT

不知不觉又停了N天学习，看来坚持对偶来说真是难于��d��啊。。�?br />

The javac compiler always looks for files in the current directory, but the java interpreter only looks into the current directory if the "." directory is on the class path. If you have no class path set, this is not a problem—the default class path consists of the "." directory. But if you have set the class path and forgot to include the "." directory, then your programs will compile without error, but they won't run.

Features tagged as public can be used by any class. Private features can be used only by the class that defines them. If you don't specify either public or private, then the feature (that is, the class, method, or variable) can be accessed by all methods in the same package.

Comment Extraction

Here, docDirectory is the name of the directory where you want the HTML files to go. Follow these steps:

1.	Change to the directory that contains the source files you want to document. If you have nested packages to document, such as `com.horstmann.corejava`, you must be working in the directory that contains the subdirectory `com`. (This is the directory that contains the `overview.html` file if you supplied one.)
2.	Run the command `javadoc -d` docDirectory nameOfPackage for a single package. Or run `javadoc -d` docDirectory nameOfPackage`₁` nameOfPackage`₂...` to document multiple packages. If your files are in the default package, then instead run `javadoc -d` docDirectory `*.java`

Benjamine 2010-12-10 12:00 发表评论

Core Java学习�W�记(�?

Benjamine — Sun, 10 Oct 2010 10:10:00 GMT

用System.out.printf�Ҏ��q�行格式化输出；也可用String.format�Ҏ��创徏一个格式化的String, 而不需要打印输出�?br />
日期格式讄��参考Core Java, Volumn 1的P55��，许多格式化规则与本地环境有关�?br />
java.util.Arrays�c�d��含了用来操作数组(例如排序与搜�?的各�U�方法，常用�Ҏ��如下:

static String toString(type[] a)

static void sort(type[] a) //Quick Sort

static int binarySearcch(type[] a, type v)

static void fill(type[] a, type v) //��数�l�的所有数据元素��D��为v

....

End of Chapter 3

Benjamine 2010-10-10 18:10 发表评论

Benjamine — Sat, 02 Oct 2010 09:57:00 GMT

Java��d��控制台System.in 输入相对�ȝ��点，要先构造一个Scanner对象�Q��ƈ与标准输入流System.in兌��?Scanner包含在包java.util�?

Scanner in = new Scanner(System.in);
System.out.println("What is your name?");
String name = in.nextLine(); //��L��行，因�ؓ可能包括�I�格

//Or
//String name = in.next(); //以空白符为分�?br /> //int age = in.nextInt(); //��d��整数

使用Scanner时输入是可见的，因此不适用从控制台��d��密码。Console�c�d��以实现这个目的�?br />

        Console cons = System.console();

        //Method prototype:
        //static String readLine(String prompt, Objectargs)
        //昄��字符串prompt�q�且��d��用户输入直到输入行结�? args参数用来提供输入格式
        String username = cons.readLine("User name: ");

        //Method prototype:
        //static char[] readPassword(String prompt, Objectargs)
        //用户输入不可�?/span>
        char[] pwd = cons.readPassword();

Benjamine 2010-10-02 17:57 发表评论

Core Java学习�W�记(�?

Benjamine — Sat, 02 Oct 2010 09:22:00 GMT

Java中有8�U�基本数据类型：int, short, long, byte, float, double, char, boolean

�?/span>Java中，整型的范围与�q�行java代码的机器无兟뀂在C/C++�E�序中，int�c�d��占用的字节可能会因不同机器不同操作系�l�而不同；而在java中，各种整型的存储需求已�l�被明确定义(int: 4 bytes; short: 2 bytes; long: 8 bytes; byte: 1 byte)�Q�从而实��C��q�_��无关性�?/span>

常用整型、��Q点型帔R��Q?/span>

l Integer.MAX_VALUE

l Ingeger.MIN_VALUE

l Double.POSITIVE_INFINITY (正无�I�大)

l Double.NEGATIVE_INFINITY (负无�I�大)

l Double.NaN (Not a number)

PS: 判断一个特定值是否等�?/span>Double.NaN:

if (x == Double.NaN) //is never true

Should use:

if (Double.isNaN(x)) // check whether x is “Not a number”

char �c�d��用于表示Unicode�~�码的字�W�单元�?/span>Unicode可表�C�Zؓ16�q�制��|��?/span>"u0000�?/span>"uffff�?/span>

关于Unicode: �?/span>Unicode出现前，已经有了很多的字�W�编码标�?/span>(如美国的ASCII, 西欧�?/span>ISO 8859-1, 俄罗斯的KOI-8, 中国�?/span>GB118030�?/span>BIG-5�Q?/span>etc)�Q�这样造成了两个问题：a). 对于�l�定的代码��|��不同的编码方案下可能对应不同的字�?/span>; b). 采用大字�W�集的语�a�其编码长度可能不同，e.g., 有些常用的字�W�采用单字节�~�码�Q�而另一些字�W�则需要两个或更多字节�?/span>设计Unicode��是��Z��解决�q�些问题。但遗憾的是�Q�经�q�一�D�|��_��Unicode字符��过�?/span>65536个，现在�Q�连16位的char�c�d��也已�l�不能满��x��?/span>Unicode字符的需求了�?span style="color: red">强烈��不要在程序中�?/span>char�c�d��?/span>

当将一个字�W�串和一个非字符串的��D��行拼接时�Q�后者被转换成字�W�串�?/span>E.g:

int age = 24;

String s = “abce” + age; //age被�{换成字符�Ԍ��l�果�?#8220;abcd24”�?br />

采用字符串连接的方式�Ӟ��每次�q�接字符�Ԍ��都会构徏一个新的String对象�Q�既耗时又浪费空间。可以��用StringBuilder代替:

StringBuilder builder = new StringBuilder();
builder.append(ch/str);
其前�w�是StringBuffer。StringBuffer效率�E�低�Q�但支持多线�E�。StringBuilder不支持多�U�程�Q�从而效率也较高�?

Benjamine 2010-10-02 17:22 发表评论

Core Java学习�W�记(一)

Benjamine — Mon, 27 Sep 2010 16:40:00 GMT

Command: jar xvf file.zip 用于解压文�g。Java库源文�g在JDK中保存�ؓsrc.zip�Q�可用该命��o解压�?br />

Javac��?java文�g�~�译�?class文�g�Q�发送到jvm, jvm执行�~�译器存攑֜�.class文�g中的字节码�?

�q�行applet�Q?). 直接用浏览器打开html�Q�该html里包含applet�?). appletviewer ***.html。applet嵌入到html的写法如�?

            ......

Benjamine 2010-09-28 00:40 发表评论