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In Java, every variable has a type. You declare a variable by placing the type first, followed by the name of the variable. Here are some examples:

在Java中，每個變量都有一個類型。你可以用把類型寫在前面，后面緊跟變量名的方式來聲明變量。下面是一些例子：

double salary;

int vacationDays;

long earthPopulation;

boolean done;

Notice the semicolon at the end of each declaration. The semicolon is necessary because a declaration is a complete Java statement.

注意每一個聲明后面的分號。由于每個聲明都是一條完整的Java語句，所以分號是必須寫的。

A variable name must begin with a letter and must be a sequence of letters or digits. Note that the terms "letter" and "digit" are much broader in Java than in most languages. A letter is defined as 'A'–'Z', 'a'–'z', '_', or any Unicode character that denotes a letter in a language. For example, German users can use umlauts such as '?' in variable names; Greek speakers could use a p. Similarly, digits are '0'–'9' and any Unicode characters that denote a digit in a language. Symbols like '+' or '?' cannot be used inside variable names, nor can spaces. All characters in the name of a variable are significant and case is also significant. The length of a variable name is essentially unlimited.

變量名必須以字母開頭的一串字母或數(shù)字序列。注意，Java中所說的“字母”和“數(shù)字”比大多數(shù)編程語言要寬泛的多。字母是指'A'–'Z', 'a'–'z', '_',或者任何在某種語言中表示某個字母的Unicode字符。例如，德國人可以在變量名中使用元音變音'?'；希臘人可以使用p。類似的，數(shù)字也是'0'–'9'或者任何在某種語言中表示一個數(shù)位的Unicode字符。諸如'+' or '?'此類的字符也不能被用于變量名，空格也不可以。所有的變量名中的字符乃至大小寫都是有意義的。變量名的長度幾乎是沒有限制的。

TIP

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If you are really curious as to what Unicode characters are "letters" as far as Java is concerned, you can use the isJavaIdentifierStart and isJavaIdentifierPart methods in the Character class to check.

提示

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如果你真的像關(guān)心Java那樣對于何種Unicode字符屬于“字母”感到好奇的話，不妨用Character類中的isJavaIdentifierStart和isJavaIdentifierPart方法去檢查。

You also cannot use a Java reserved word for a variable name. (See Appendix A for a list of reserved words.)

你不能用Java保留字作為變量名。

You can have multiple declarations on a single line:

你可以在同一行聲明多個變量：

int i, j; // both are integers

However, we don't recommend this style. If you declare each variable separately, your programs are easier to read.

但是，我們并不推薦使用這種方式。如果你分別聲明每一個變量，你的程序可讀性更好。

NOTE

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As you saw, names are case sensitive, for example, hireday and hireDay are two separate names. In general, you should not have two names that only differ in their letter case. However, sometimes it is difficult to come up with a good name for a variable. Many programmers then give the variable the same name of the type, such as

Box box; // ok--Box is the type and box is the variable name

Other programmers prefer to use an "a" prefix for the variable:

Box aBox;

注釋

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如你所見，命名是區(qū)分大小寫的，例如，hireday和hireDay是兩個不同的名字。通常，你不應該僅僅通過大小寫來區(qū)分兩個命名。但是，有時候很難給一個變量起一個好名字。很多程序員就用與類型名相同的名字來給變量命名，例如：

Box box; // ok--Box 是個類型而 box 是變量名

有的程序員喜歡給變量名加上一個“a”前綴：

Box aBox;

Initializing Variables變量初始化

After you declare a variable, you must explicitly initialize it by means of an assignment statement—you can never use the values of uninitialized variables. For example, the Java compiler flags the following sequence of statements as an error:

聲明變量以后，你必須明確的用一個賦值語句對其初始化——你絕不能夠使用一個沒有初始化的變量。例如，Java編譯器將會標記如下語句為一個錯誤：

int vacationDays;

System.out.println(vacationDays); // ERROR--variable not initialized

You assign to a previously declared variable by using the variable name on the left, an equal sign (=), and then some Java expression that has an appropriate value on the right.

給變量賦值時，你可以把先前聲明好的變量名寫在左邊，再寫一個等號(=)，然后右邊緊跟一些Java具有適當值的表達式。

int vacationDays;

vacationDays = 12;

You can both declare and initialize a variable on the same line. For example:

你也可以把變量的聲明和初始化寫在一行，例如：

int vacationDays = 12;

Finally, in Java you can put declarations anywhere in your code. For example, the following is valid code in Java:

最后要說明的，在Java中，你可以把變量的聲明放在你代碼的任何地方。比如，下面的代碼在Java中是正確的：

double salary = 65000.0;

System.out.println(salary);

int vacationDays = 12; // ok to declare a variable here

In Java, it is considered good style to declare variables as closely as possible to the point where they are first used.

在Java中，一種比較好的方式就是聲明變量以后緊接著指出該變量第一次使用的位置。

C++ NOTE

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C and C++ distinguish between the declaration and definition of variables. For example,

int i = 10;

is a definition, whereas

extern int i;

is a declaration. In Java, no declarations are separate from definitions.

C++ 附注

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C和C++中區(qū)分聲明和定義。例如：

int i = 10;

是一個定義，而

extern int i;

是一個聲明。在Java中，沒有獨立于定義的聲明。

Constants常量

In Java, you use the keyword final to denote a constant. For example,

在Java中，你可以用關(guān)鍵字final來指明一個常量，例如：

public class Constants

{

public static void main(String[] args)

{

final double CM_PER_INCH = 2.54;

double paperWidth = 8.5;

double paperHeight = 11;

System.out.println("Paper size in centimeters: "

+ paperWidth * CM_PER_INCH + " by " + paperHeight * CM_PER_INCH);

}

}

The keyword final indicates that you can assign to the variable once, and then its value is set once and for all. It is customary to name constants in all upper case.

關(guān)鍵字final指出你可以給變量賦值一次，而其值也只能設(shè)置一次。通常習慣上將常量名全部大寫。

It is probably more common in Java to want a constant that is available to multiple methods inside a single class. These are usually called class constants. You set up a class constant with the keywords static final. Here is an example of using a class constant:

在Java中，我們或許更多時候需要一個能被一個類中的多個方法使用的常量。這種常量被稱之為類常量。類常量用關(guān)鍵字static final來設(shè)置。下面是一個使用類常量的例子：

public class Constants2

{

public static void main(String[] args)

{

double paperWidth = 8.5;

double paperHeight = 11;

System.out.println("Paper size in centimeters: "

+ paperWidth * CM_PER_INCH + " by " + paperHeight * CM_PER_INCH);

}

public static final double CM_PER_INCH = 2.54;

}

Note that the definition of the class constant appears outside the main method. Thus, the constant can also be used in other methods of the same class. Furthermore, if (as in our example) the constant is declared public, methods of other classes can also use the constant—in our example, as Constants2.CM_PER_INCH.

注意到對類常量的定義出現(xiàn)在了主方法的外面。正因為如此，類常量也可以被同類的其他方法訪問。此外，如果（如我們的例子）常量被聲明為public，那么其他類的方法也可以使用這個常量——在我們的例子中，就像Constants2中的CM_PER_INCH一樣。

C++ NOTE

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const is a reserved Java keyword, but it is not currently used for anything. You must use final for a constant.

C++ 注釋

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const是一個Java預留的關(guān)鍵字，但是現(xiàn)在不再用于任何場合。你必須使用final來定義常量。

Java is a strongly typed language. This means that every variable must have a declared type. There are eight primitive types in Java. Four of them are integer types; two are floating-point number types; one is the character type char, used for code units in the Unicode encoding scheme (see the section on the char type); and one is a boolean type for truth values.

Java是一種強類型語言。這意味著每個變量必須聲明類型。Java中有八種原始類型。其中4種是整數(shù)類型；兩種是浮點數(shù)類型；一種是字符類型char，適用于Unicode編碼方案中的代碼單元（參見本節(jié)中的char類型小節(jié)）；還有一種是用來表示真值的布爾類型。

NOTE注釋

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Java has an arbitrary precision arithmetic package. However, "big numbers," as they are called, are Java objects and not a new Java type. You see how to use them later in this chapter.

Java有一個任意精度的算術(shù)包。顧名思義，“大數(shù)”是一個Java對象，而并非新的Java類型。你將在本章后面看到如何使用它們。

Integers整數(shù)

The integer types are for numbers without fractional parts. Negative values are allowed. Java provides the four integer types shown in Table 3-1.

整數(shù)類型是四種無小數(shù)部分的數(shù)字，允許負值。Java提供表3-1所示的四種整數(shù)類型。

Table 3-1. Java Integer Types

類型

存儲空間

范圍（閉區(qū)間）

Int

4 字節(jié)

–2,147,483,648 to 2,147,483, 647 (超過20億)

Short

2字節(jié)

–32,768 to 32,767

Long

8字節(jié)

–9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

Byte

1字節(jié)

–128 to 127

In most situations, the int type is the most practical. If you want to represent the number of inhabitants of our planet, you'll need to resort to a long. The byte and short types are mainly intended for specialized applications, such as low-level file handling, or for large arrays when storage space is at a premium.

大多數(shù)情況下，int類型是最實用的。如果你想表示我們星球上居民的數(shù)量，你就需要訴諸于long類型。Byte和short類型主要用于一些特殊的應用，比如較低級的文件處理，或者當存儲空間非常珍貴的時候處理大的數(shù)組。

Under Java, the ranges of the integer types do not depend on the machine on which you will be running the Java code. This alleviates a major pain for the programmer who wants to move software from one platform to another, or even between operating systems on the same platform. In contrast, C and C++ programs use the most efficient integer type for each processor. As a result, a C program that runs well on a 32-bit processor may exhibit integer overflow on a 16-bit system. Because Java programs must run with the same results on all machines, the ranges for the various types are fixed.

Long integer numbers have a suffix L (for example, 4000000000L). Hexadecimal numbers have a prefix 0x (for example, 0xCAFE). Octal numbers have a prefix 0. For example, 010 is 8. Naturally, this can be confusing, and we recommend against the use of octal constants.

在Java中，整數(shù)類型的范圍不取決于你運行Java代碼的機器。這避免了將軟件在兩個平臺或者在同一平臺上的兩個操作系統(tǒng)之間轉(zhuǎn)移而帶來的主要麻煩。與之相反的是，C和C++程序?qū)γ總€處理器使用最有效的整數(shù)類型。造成的結(jié)果就是，一個C程序在一個32位處理器上運行良好而在一個16位系統(tǒng)中可能表現(xiàn)出整數(shù)溢出。因為Java程序必須保證在所有的機器上運行得到相同的結(jié)果，不同類型的范圍是固定的。長整型數(shù)字有一個L后綴（例如4000000000L）。十六位數(shù)字有一個0x前綴（例如，0xCAFE）。八進制數(shù)字有一個0前綴。例如，010就是8。當然，這可能導致混淆，所以我們建議避免使用八進制數(shù)。

C++ NOTE C++注釋

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In C and C++, int denotes the integer type that depends on the target machine. On a 16-bit processor, like the 8086, integers are 2 bytes. On a 32-bit processor like the Sun SPARC, they are 4-byte quantities. On an Intel Pentium, the integer type of C and C++ depends on the operating system: for DOS and Windows 3.1, integers are 2 bytes. When 32-bit mode is used for Windows programs, integers are 4 bytes. In Java, the sizes of all numeric types are platform independent.

Note that Java does not have any unsigned types.

在C和C++中，int表示的整數(shù)類型取決于目標機。在16位處理器上，例如8086機，整數(shù)占用2字節(jié)。在32位處理器，例如Sun公司的SPARC，整數(shù)占用4字節(jié)。在Intel奔騰上，C和C++的整數(shù)類型取決于操作系統(tǒng)：對于DOS和Windows3.1，整數(shù)是2字節(jié)。當Windows程序使用32位模式時，整數(shù)占用4字節(jié)。在Java中，一切數(shù)字類型的大小都是平臺無關(guān)的。注意，Java沒有任何無符號類型。

Floating-Point Types浮點類型

The floating-point types denote numbers with fractional parts. The two floating-point types are shown in Table 3-2.

浮點類型表示的數(shù)字含有小數(shù)部分。表3-2顯示了兩種浮點類型。

Table 3-2. Floating-Point Types

類型

存儲空間

范圍

float

4字節(jié)

大約 ±3.40282347E+38F (6–7 個有效十進制位)

double

8字節(jié)

大約 ±1.79769313486231570E+308 (15個有效十進制位)

The name double refers to the fact that these numbers have twice the precision of the float type. (Some people call these double-precision numbers.) Here, the type to choose in most applications is double. The limited precision of float is simply not sufficient for many situations. Seven significant (decimal) digits may be enough to precisely express your annual salary in dollars and cents, but it won't be enough for your company president's salary. The only reasons to use float are in the rare situations in which the slightly faster processing of single-precision numbers is important or when you need to store a large number of them.

Numbers of type float have a suffix F (for example, 3.402F). Floating-point numbers without an F suffix (such as 3.402) are always considered to be of type double. You can optionally supply the D suffix (for example, 3.402D).

Double這個名字說明該類型具有兩倍于float類型的精度。（有人將之稱為雙精度數(shù)字。）這里，大多數(shù)應用程序選擇double類型。Float類型有限的精度對于許多情況都是不足的。七個有效的十進制位也許用來以美元和美分的單位表示你的年薪還是足夠的，但是用來表示你公司老總的薪水就顯得不夠了。僅當極少數(shù)需要對單精度數(shù)字進行敏捷的處理或者需要存儲大量單精度數(shù)字的時候，才有理由使用float類型。

As of JDK 5.0, you can specify floating-point numbers in hexadecimal. For example, 0.125 is the same as 0x1.0p-3. In hexadecimal notation, you use a p, not an e, to denote the exponent.

從JDK5.0起，你可以指定十六進制的浮點數(shù)字。例如，0.125就等同于0x1.0p-3。在十六進制符號中，采用p而非e來表示指數(shù)。

All floating-point computations follow the IEEE 754 specification. In particular, there are three special floating-point values:

positive infinity

negative infinity

NaN (not a number)

to denote overflows and errors. For example, the result of dividing a positive number by 0 is positive infinity. Computing 0/0 or the square root of a negative number yields NaN.

所有浮點計算遵循IEEE 754規(guī)范。特別的，有三種特殊的浮點值：

positive infinity正無窮

negative infinity負無窮

NaN (非數(shù)字)

來表示溢出和錯誤。例如，將一個正數(shù)除以0得到的結(jié)果就是正無窮。0/0或者負數(shù)的平方根就是NaN。

NOTE注釋

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The constants Double.POSITIVE_INFINITY, Double.NEGATIVE_INFINITY, and Double.NaN (as well as corresponding Float constants) represent these special values, but they are rarely used in practice. In particular, you cannot test

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

to check whether a particular result equals Double.NaN. All "not a number" values are considered distinct. However, you can use the Double.isNaN method:

if (Double.isNaN(x)) // check whether x is "not a number"

常量Double.POSITIVE_INFINITY、Double.NEGATIVE_INFINITY、Double.NaN（以及相應的Float常量）表示以上特殊值。但它們在實際應用中非常少用。特別的，你無法測試

if(x==Double.NaN)//永不為真

來檢查實際結(jié)果是否等于Double.NaN。所有“非數(shù)字”值被歸為獨特的。但是你可以使用Double.isNaN方法。

if (Double.isNaN(x)) // 檢測x是否是“非數(shù)字”。

CAUTION注意

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Floating-point numbers are not suitable for financial calculation in which roundoff errors cannot be tolerated. For example, the command System.out.println(2.0 - 1.1) prints 0.8999999999999999, not 0.9 as you would expect. Such roundoff errors are caused by the fact that floating-point numbers are represented in the binary number system. There is no precise binary representation of the fraction 1/10, just as there is no accurate representation of the fraction 1/3 in the decimal system. If you need precise numerical computations without roundoff errors, use the BigDecimal class, which is introduced later in this chapter.

浮點數(shù)字在不能容忍循環(huán)錯誤的財政計算中是不合適的。例如，System.out.println(2.0 - 1.1) 命令打印出 0.8999999999999999, 而非你期望得到的0.9。這種循環(huán)錯誤是由于在二進制系統(tǒng)中表示浮點數(shù)而引起的。對于分數(shù)1/10沒有精確的二進制表示，正如對于分數(shù)1/3沒有精確的十進制表示一樣。如果你需要沒有循環(huán)錯誤的精確數(shù)值計算，請使用BigDecimal類，這將在本章稍后介紹。

The char Type char類型

To understand the char type, you have to know about the Unicode encoding scheme. Unicode was invented to overcome the limitations of traditional character encoding schemes. Before Unicode, there were many different standards: ASCII in the United States, ISO 8859-1 for Western European languages, KOI-8 for Russian, GB18030 and BIG-5 for Chinese, and so on. This causes two problems. A particular code value corresponds to different letters in the various encoding schemes. Moreover, the encodings for languages with large character sets have variable length: some common characters are encoded as single bytes, others require two or more bytes.

要理解char類型，你需要了解Unicode編碼規(guī)則。Unicode是為克服傳統(tǒng)字符編碼規(guī)則的局限性而發(fā)明的。在Unicode之前，有許多標準：美國的ASCII、西歐語言的ISO 8859-1、俄語使用的KOI-8、中文使用的GB18030 和 BIG-5等等。這造成了兩個問題。一個特定的碼值在不同的編碼規(guī)則中對應于不同的字母。此外，大字符集的語言使用的編碼具有可變的長度：一些普通的字符以單字節(jié)編碼，而其余的需要兩個或更多字節(jié)。

Unicode was designed to solve these problems. When the unification effort started in the 1980s, a fixed 2-byte width code was more than sufficient to encode all characters used in all languages in the world, with room to spare for future expansion—or so everyone thought at the time. In 1991, Unicode 1.0 was released, using slightly less than half of the available 65,536 code values. Java was designed from the ground up to use 16-bit Unicode characters, which was a major advance over other programming languages that used 8-bit characters.

Unicode的初衷就是解決這個問題。在統(tǒng)一化進程始于20世紀80年代的時候，一個定長的兩字節(jié)碼已經(jīng)足夠?qū)κ澜缟纤姓Z言中的所有字符進行編碼，剩下的空間還可以用于將來的擴展——大概當初每個人都是這樣認為的。1991年，Unicode 1.0誕生了，僅使用了全部可用65536個碼值中的一半。Java被設(shè)計為完全采用16位Unicode字符，這是Java優(yōu)于其他采用8位字符的一個主要優(yōu)點。

Unfortunately, over time, the inevitable happened. Unicode grew beyond 65,536 characters, primarily due to the addition of a very large set of ideographs used for Chinese, Japanese, and Korean. Now, the 16-bit char type is insufficient to describe all Unicode characters.

We need a bit of terminology to explain how this problem is resolved in Java, beginning with JDK 5.0. A code point is a code value that is associated with a character in an encoding scheme. In the Unicode standard, code points are written in hexadecimal and prefixed with U+, such as U+0041 for the code point of the letter A. Unicode has code points that are grouped into 17 code planes. The first code plane, called the basic multilingual plane, consists of the "classic" Unicode characters with code points U+0000 to U+FFFF. Sixteen additional planes, with code points U+10000 to U+10FFFF, hold the supplementary characters.

不幸的是，隨著時間的過去，不可避免的事情發(fā)生了。Unicode超過了65535個字符，主要是由于像中文、日文、韓文這樣的大量的象形文字的加入而造成的。現(xiàn)在，16位char類型已經(jīng)不足以描述所有Unicode字符。

我們需要使用一點術(shù)語來解釋這個問題在Java中，從JDK5.0開始是如何得以解決的。一個代碼點就是一個編碼規(guī)則中與一個字符相關(guān)聯(lián)的碼值。在Unicode標準中，代碼點是用16進制寫成，加上U+前綴，例如U+0041就是字母A的代碼點。Unicode的代碼點被分成17個代碼組。第一個代碼組叫做基本多語言組，是由采用U+0000至U+FFFF代碼點的“經(jīng)典”Unicode字符組成。額外的16個代碼組，代碼點從U+10000至U+10FFFF，保存輔助字符。

The UTF-16 encoding is a method of representing all Unicode code points in a variable length code. The characters in the basic multilingual plane are represented as 16-bit values, called code units. The supplementary characters are encoded as consecutive pairs of code units. Each of the values in such an encoding pair falls into an unused 2048-byte range of the basic multilingual plane, called the surrogates area (U+D800 to U+DBFF for the first code unit, U+DC00 to U+DFFF for the second code unit).This is rather clever, because you can immediately tell whether a code unit encodes a single character or whether it is the first or second part of a supplementary character. For example, the mathematical symbol for the set of integers has code point U+1D56B and is encoded by the two code units U+D835 and U+DD6B. (See http://en.wikipedia.org/wiki/UTF-16 for a description of the encoding algorithm.)

UTF-16編碼是一種以變長編碼表示所有Unicode代碼點的方法。基本多語言組中的字符以16位值表示，叫做代碼單元。輔助字符以連續(xù)的代碼單元對編碼。這樣一個編碼對中的每個值就屬于一個未占用的2048字節(jié)的基本多語言組范圍，稱作代理區(qū)域（U+D800至U+DBFF 表示第一個代碼單元, U+DC00至U+DFFF表示第二個代碼單元）。這是相當明智的，因為你可以立即說出一個代碼單元是否對一個單字符進行編碼或者它是輔助字符的第一部分還是第二部分。例如，整數(shù)集的算術(shù)符號的代碼點為U+1D56B，它是由兩個代碼單元U+D835和U+DD6B編碼而成。（參見http://en.wikipedia.org/wiki/UTF-16獲得有關(guān)編碼算法的描述）

In Java, the char type describes a code unit in the UTF-16 encoding.

Our strong recommendation is not to use the char type in your programs unless you are actually manipulating UTF-16 code units. You are almost always better off treating strings as abstract data types.

Java中，char類型描述UTF-16編碼中的一個代碼單元。

我們強烈建議在程序中避免使用char類型，除非你對UTF-16代碼單元十分熟練。你幾乎總是將字符串視為抽象數(shù)據(jù)類型即可。

Having said that, there will be some cases when you will encounter char values. Most commonly, these will be character constants. For example, 'A' is a character constant with value 65. It is different from "A", a string containing a single character. Unicode code units can be expressed as hexadecimal values that run from \u0000 to \uFFFF. For example, \u2122 is the trademark symbol (?) and \u03C0 is the Greek letter pi (p).

盡管如上所述，但是有時候你也會遇到char值。最常見的就是字符常量。例如，‘A’是一個值為65的字符常量。它與“A”這個僅包含一個字符的字符串不同。Unicode代碼單元可被表示成從\u0000到\uFFFF的十六進制值。例如，\u2122是商標符號(?) 而 \u03C0 是希臘字母 (p).

Besides the \u escape sequences that indicate the encoding of Unicode code units, there are several escape sequences for special characters, as shown in Table 3-3. You can use these escape sequences inside quoted character constants and strings, such as '\u2122' or "Hello\n". The \u escape sequence (but none of the other escape sequences) can even be used outside quoted character constants and strings. For example,

public static void main(String\5B\5D args)

除了用\u轉(zhuǎn)義符來表示Unicode代碼單元的編碼，還有一些特殊的轉(zhuǎn)義符來表示特殊字符，如表3-3所示。你可以在用引號引起來的字符常量和字符串中使用這些轉(zhuǎn)義符，例如'\u2122'或"Hello\n"。\u轉(zhuǎn)義符（但其他轉(zhuǎn)義符除外）甚至可以在引號引起來的字符常量和字符串外使用。例如：public static void main(String\5B\5D args)

Table 3-3. Escape Sequences for Special Characters

Escape Sequence

Name

Unicode Value

\b

退格

\u0008

\t

Tab

\u0009

\n

換行

\u000a

\r

回車

\u000d

\"

雙引號

\u0022

\'

單引號

\u0027

\\

反斜線

\u005c

is perfectly legal—\u005B and \u005D are the UTF-16 encodings of the Unicode code points for [ and ].

是完全合法的——\u005B和\u005D 是“[”和“]”的Unicode代碼點的UTF-16編碼。

NOTE注釋

?

Although you can use any Unicode character in a Java application or applet, whether you can actually see it displayed depends on your browser (for applets) and (ultimately) on your operating system for both.

盡管你可以在任何Java程序和Applet中使用Unicode字符，但實際上你能否看到這些字符還要取決于你的瀏覽器（對Applet而言）和你的操作系統(tǒng)（這是最基本的）。

The boolean Type boolean類型（也作布爾類型）

The boolean type has two values, false and true. It is used for evaluating logical conditions. You cannot convert between integers and boolean values.

boolean類型有兩個值，false和true。這是用來判斷邏輯條件的。你不能在整型和布爾型之間進行轉(zhuǎn)換。

C++ NOTE C++注釋

?

In C++, numbers and even pointers can be used in place of boolean values. The value 0 is equivalent to the bool value false, and a non-zero value is equivalent to true. This is not the case in Java. Thus, Java programmers are shielded from accidents such as

if (x = 0) // oops...meant x == 0

In C++, this test compiles and runs, always evaluating to false. In Java, the test does not compile because the integer expression x = 0 cannot be converted to a boolean value.

在C++中，數(shù)字乃至小數(shù)點都被用于替代布爾值。0值就相當于布爾值false而非0值相當于true。Java中并非如此。因此Java程序員不會遇到下面的情況：

if (x = 0) // 哇。。。意味著x==0

C++中，這個測試可以編譯并運行，并且總是判斷為false。在Java中，這個測試無法編譯，因為整型表達式x=0不能被轉(zhuǎn)換為布爾值。

Comments in Java, like comments in most programming languages, do not show up in the executable program. Thus, you can add as many comments as needed without fear of bloating the code. Java has three ways of marking comments. The most common method is a //. You use this for a comment that will run from the // to the end of the line.

Java中的注釋，和大多數(shù)編程語言中的注釋一樣，在可執(zhí)行程序中不會顯示。因此，你可以根據(jù)需要任意添加注釋而不必擔心導致代碼膨脹。Java有三種注釋方法。最普通的是用一個//符號。用這個符號來注釋從//開始到一行結(jié)尾的內(nèi)容。

System.out.println("We will not use 'Hello, World!'"); // is this too cute?

When longer comments are needed, you can mark each line with a //. Or you can use the /* and */ comment delimiters that let you block off a longer comment. This is shown in Example 3-1.

當需要更長的注釋的時候，你可以用//來注釋每一行。或者你也可以使用/*和*/這兩個注釋定界符來隔離一個較長的注釋。如例子3-1所示

Example 3-1. FirstSample.java

1. /*

2. This is the first sample program in Core Java Chapter 3

3. Copyright (C) 1997 Cay Horstmann and Gary Cornell

4. */

5.

6. public class FirstSample

7. {

8.????? public static void main(String[] args)

9.????? {

10.??????????? System.out.println("We will not use 'Hello, World!'");

11.???? }

12. }

Finally, a third kind of comment can be used to generate documentation automatically. This comment uses a /** to start and a */ to end. For more on this type of comment and on automatic documentation generation, see Chapter 4.

最后，第三種注釋用于自動生成文檔。該注釋以/**開始以*/結(jié)束。有關(guān)這種注釋和自動生成文檔的更多內(nèi)容，請見第四章。

CAUTION注意

?

/* */ comments do not nest in Java. That is, you cannot deactivate code simply by surrounding it with /* and */ because the code that you want to deactivate might itself contain a */ delimiter.

/* */注釋在Java中是不可嵌套的。也就是說，當你想要注釋掉一段代碼的時候，你不能簡單的使用/*和*/，因為你想注釋掉的代碼可能就含有一個*/定界符。

Let's look more closely at about the simplest Java program you can have—one that simply prints a message to the console window:

讓我們更進一步來看一個最簡單的向控制臺窗口輸出信息的Java程序。

?

It is worth spending all the time that you need to become comfortable with the framework of this sample; the pieces will recur in all applications. First and foremost, Java is case sensitive. If you made any mistakes in capitalization (such as typing Main instead of main), the program will not run.

你需要花費來熟悉這個例子的框架，這是值得的，因為這個框架將在所有應用程序中重現(xiàn)。首先，Java是大小寫敏感的。如果你在大小寫上犯了錯誤（例如把Main寫成main），程序就不會運行。

Now let's look at this source code line by line. The keyword public is called an access modifier; these modifiers control the level of access other parts of a program have to this code. We have more to say about access modifiers in Chapter 5. The keyword class reminds you that everything in a Java program lives inside a class. Although we spend a lot more time on classes in the next chapter, for now think of a class as a container for the program logic that defines the behavior of an application. As mentioned in Chapter 1, classes are the building blocks with which all Java applications and applets are built. Everything in a Java program must be inside a class.

現(xiàn)在讓我們一行行地來閱讀這段代碼。關(guān)鍵字public被稱作訪問修飾符；這些修飾符控制著這段代碼對一個程序其他部分的訪問權(quán)限。在第五章中我們將對訪問修飾符做更多討論。關(guān)鍵字class說明Java程序中的一切都是存在于類當中。盡管在下一章中我們將花費更多時間來講述類，但現(xiàn)在我們不妨把類想像成一個承載描述應用行為的程序邏輯的容器。正如在第一章中提到的，類是一切Java應用程序和applet的構(gòu)建模塊。Java程序中的一切必須存在于類中。

Following the keyword class is the name of the class. The rules for class names in Java are quite generous. Names must begin with a letter, and after that, they can have any combination of letters and digits. The length is essentially unlimited. You cannot use a Java reserved word (such as public or class) for a class name. (See Appendix A for a list of reserved words.)

關(guān)鍵字class后面的就是類名。Java當中類的命名規(guī)則是相當寬松的。類名必須以字母開始，其后可以是任意字母和數(shù)字的組合。類名的長度基本上是無限的。你不可以使用Java保留字來作為類名。（保留字列表請參見附錄A）

The standard naming convention (which we follow in the name FirstSample) is that class names are nouns that start with an uppercase letter. If a name consists of multiple words, use an initial uppercase letter in each of the words. (This use of uppercase letters in the middle of a word is sometimes called "camel case" or, self-referentially, "CamelCase.")

標準的命名規(guī)則是類名需是以一個大寫字母開頭的名詞（如FirstSample這個名字中遵循的規(guī)則）。如果一個類名以多個單詞組成，則每個單詞使用首字母規(guī)則。（這種在一個詞中間使用大寫字母的用法有時又叫做“camel case”，或者形象的寫作“CamelCase”）

You need to make the file name for the source code the same as the name of the public class, with the extension .java appended. Thus, you must store this code in a file called FirstSample.java. (Again, case is important—don't use firstsample.java.)

你需要使文件名和public類的名字相同，后面加上.java擴展名。因此，你需要將以上代碼存儲到一個文件名為FirstSample.java的文件中。（再次說明，大小寫很重要，不要寫成firstsimple.java）

If you have named the file correctly and not made any typos in the source code, then when you compile this source code, you end up with a file containing the bytecodes for this class. The Java compiler automatically names the bytecode file FirstSample.class and stores it in the same directory as the source file. Finally, launch the program by issuing the command:

如果你正確給文件命名并且沒有在源代碼中寫入任何打字稿，那么當你編譯這個源文件時，你將得到一個屬于這個類的包含字節(jié)碼的文件。Java編譯器會自動把字節(jié)碼文件命名為FirstSimple.class并將其存儲在Java源文件的同一目錄下。最后用如下命令來啟動程序：

java FirstSample

(Remember to leave off the .class extension.) When the program executes, it simply displays the string We will not use 'Hello, World'! on the console.

（切記去掉.class擴展名）程序執(zhí)行時，將在控制臺簡單輸出一個字符串：We will not use ‘Hello,World’!

When you use

當你用

java?ClassName

to run a compiled program, the Java virtual machine always starts execution with the code in the main method in the class you indicate. Thus, you must have a main method in the source file for your class for your code to execute. You can, of course, add your own methods to a class and call them from the main method. (We cover writing your own methods in the next chapter.)

來運行一個已經(jīng)編譯的程序時，Java虛擬機總是從你指定的類當中的main方法開始執(zhí)行。當然你也可以在一個類中添加你自己的方法，并將之成為是main方法。（我們將在下一章中討論編寫自定義方法。）

NOTE

注意

?

According to the Java Language Specification, the main method must be declared public. (The Java Language Specification is the official document that describes the Java language. You can view or download it from http://java.sun.com/docs/books/jls.) However, several versions of the Java launcher were willing to execute Java programs even when the main method was not public. A programmer filed a bug report. To see it, visit the site http://bugs.sun.com/bugdatabase/index.jsp and enter the bug identification number 4252539. However, that bug was marked as "closed, will not be fixed." A Sun engineer added an explanation that the Java Virtual Machine Specification (at http://java.sun.com/docs/books/vmspec) does not mandate that main is public and that "fixing it will cause potential troubles." Fortunately, sanity finally prevailed. The Java launcher in JDK 1.4 and beyond enforces that the main method is public.

根據(jù)Java語言規(guī)范，main方法必須被聲明為public。（Java語言規(guī)范是描述Java語言的官方文檔。你可以從http://java.sun.com/docs/books/jls下載并查看）然而，有些版本的Java啟動器在main方法不是public的時候也會執(zhí)行Java程序。一個程序員提交了一個bug報告。請訪問站點http://bugs.sun.com/bugdatabase/index.jsp 并輸入bug標識號4252539來查看這個報告。然而這個bug被標記為“關(guān)閉，將不予修正”。一個Sun的工程師添加了一條解釋，即Java虛擬機規(guī)范（http://java.sun.com/docs/books/vmspec）不要求main方法為public，并且“修正這個問題將導致潛在的麻煩.”幸運的是，心智健全最終獲勝。JDK1.4及以上版本的Java啟動器強制main方法為public。

There are a couple of interesting aspects about this story. On the one hand, it is frustrating to have quality assurance engineers, who are often overworked and not always experts in the fine points of Java, make questionable decisions about bug reports. On the other hand, it is remarkable that Sun puts the bug reports and their resolutions onto the Web, for anyone to scrutinize. The "bug parade" is a very useful resource for programmers. You can even "vote" for your favorite bug. Bugs with lots of votes have a high chance of being fixed in the next JDK release.

關(guān)于這個故事有兩個有趣的方面。一方面，讓那些經(jīng)常過勞工作的且不專于Java的細琢的質(zhì)量保證工程師對bug報告做出充滿問題的決議是一件讓人沮喪的事情。另一方面，值得注意的是Sun公司將bug報告和他們的決議放在網(wǎng)上，供大家細察。Bug檢閱對程序員來說是一個很有用處的資源。你甚至可以為你最青睞的bug投票。那些票數(shù)最高的bug將會有很大的幾率在下一版的JDK中被修復。

Notice the braces { } in the source code. In Java, as in C/C++, braces delineate the parts (usually called blocks) in your program. In Java, the code for any method must be started by an opening brace { and ended by a closing brace }.

注意程序中的括號{ }。和在C++中一樣，在Java中，括號劃分出程序中的各個部分（通常叫做程序塊或代碼塊）。在Java中，任何方法的代碼都必須以開括號{開始，以閉括號}結(jié)束。

Brace styles have inspired an inordinate amount of useless controversy. We use a style that lines up matching braces. Because whitespace is irrelevant to the Java compiler, you can use whatever brace style you like. We will have more to say about the use of braces when we talk about the various kinds of loops.

括號的使用風格引發(fā)了大量混亂的無用爭論。我們使用一種風格將匹配括號排隊。因為空格對Java編譯器而言無關(guān)，你可以使用任何你喜歡的括號風格。我們將會在講述各種循環(huán)的時候?qū)ㄌ柕氖褂米龈嗟挠懻摗?

For now, don't worry about the keywords static void—just think of them as part of what you need to get a Java program to compile. By the end of Chapter 4, you will understand this incantation completely. The point to remember for now is that every Java application must have a main method that is declared in the following way:

現(xiàn)在，暫時不關(guān)注關(guān)鍵字static void，就把他們看作是你要編譯一個Java程序所必須的。在第四章最后，你將完全理解這個咒語。現(xiàn)在要記住的是每個Java應用程序必須有一個像下面這樣定義的main方法：

public class?ClassName
{
???? public static void main(String[] args)
???? {
?????????? program?statements
???? }
}

C++ NOTE C++注釋

?

As a C++ programmer, you know what a class is. Java classes are similar to C++ classes, but there are a few differences that can trap you. For example, in Java all functions are methods of some class. (The standard terminology refers to them as methods, not member functions.) Thus, in Java you must have a shell class for the main method. You may also be familiar with the idea of static member functions in C++. These are member functions defined inside a class that do not operate on objects. The main method in Java is always static. Finally, as in C/C++, the void keyword indicates that this method does not return a value. Unlike C/C++, the main method does not return an "exit code" to the operating system. If the main method exits normally, the Java program has the exit code 0, indicating successful completion. To terminate the program with a different exit code, use the System.exit method.

作為C++程序員，你知道類是什么。Java類和C++中的類相似。但是也有一些不同會使你陷入其中。例如，在Java中，所有的函數(shù)都是某個類的方法。（他們的標準術(shù)語叫做方法，而非成員函數(shù)。）因此，在Java中，你必須給main方法一個外殼類。你或許對C++中的靜態(tài)成員函數(shù)也很熟悉。這是一些定義在類中但不對對象進行操作的成員函數(shù)。Java中的main方法總是靜態(tài)的。最后，和在C++中一樣，void關(guān)鍵字說明該方法不返回值。與C/C++不同的是，在C/C++中，main方法不會向操作系統(tǒng)返回一個“退出碼”。而在Java中，如果main方法正常退出，Java程序?qū)⒎祷匾粋€退出碼0，以表示成功完成。要以不同的退出碼終止程序，請使用System.exit()方法。

Next, turn your attention to this fragment.

下面，請注意以下這個片段：

{

???? System.out.println("We will not use 'Hello, World!'");

}

Braces mark the beginning and end of the body of the method. This method has only one statement in it. As with most programming languages, you can think of Java statements as being the sentences of the language. In Java, every statement must end with a semicolon. In particular, carriage returns do not mark the end of a statement, so statements can span multiple lines if need be.

括號將方法體的開始和結(jié)束標記出來。方法中只有一個句子。和大多數(shù)編程語言一樣，你可以認為Java語句就是一個語言的句子。在Java中，每個句子必須以分號結(jié)束。特別要指出的是，回車并不表示語句的結(jié)束，所以在需要的情況下語句可以跨越多行。

The body of the main method contains a statement that outputs a single line of text to the console.

main方法的方法體包含一條向控制臺輸出單行文本的語句。

Here, we are using the System.out object and calling its println method. Notice the periods used to invoke a method. Java uses the general syntax

這里，我們使用了System.out對象和它的println方法。注意用于調(diào)用方法的句點。Java使用一般語法：

object.method(parameters)

for its equivalent of function calls.

來進行函數(shù)調(diào)用。

In this case, we are calling the println method and passing it a string parameter. The method displays the string parameter on the console. It then terminates the output line so that each call to println displays its output on a new line. Notice that Java, like C/C++, uses double quotes to delimit strings. (You can find more information about strings later in this chapter.)

此時，我們調(diào)用println方法并傳一個字符串參數(shù)給它。這個方法將該字符串參數(shù)顯示在控制臺中。之后就結(jié)束該輸出行，因此，每個println調(diào)用都可以將其輸出寫入一個新行。注意到Java和C++一樣，也使用雙引號來劃分字符串。（本章稍后將詳細討論字符串）

Methods in Java, like functions in any programming language, can use zero, one, or more parameters (some programmers call them arguments). Even if a method takes no parameters, you must still use empty parentheses. For example, a variant of the println method with no parameters just prints a blank line. You invoke it with the call

Java中的方法，像任何編程語言中的一樣，可以使用零個一個或者更多參數(shù)（一些程序員習慣稱之為變量）。即使有些方法沒有參數(shù)，你也必須使用空圓括號。例如，不同的無參println方法只輸出一個空行。你可以通過以下方法調(diào)用它：

System.out.println();

NOTE 注釋

?

System.out also has a print method that doesn't add a new line character to the output. For example, System.out.print("Hello") prints "Hello" without a new line. The next output appears immediately after the "o".

System.out 也有一個不換行的print方法，例如System.out.print(“Hello”)就可以輸出”Hello”而不換行。下個輸出將緊跟在“o”的后面。

終于決定好好的學習Core Java了。

我的Core Java學習筆記基本上是自己把原文翻譯一遍，然后對部分有價值的代碼進行一些討論。

學習筆記僅從最重要的部分開始。前兩章暫不涉及。

原版書籍來源于Flyheart提供的電子書。本學習筆記連載的內(nèi)容僅供自學之用，嚴禁用于任何商業(yè)用途，由此引起的任何后果本人概不負責。。。

由于本人水平有限，難免會有很多錯誤，希望大家多多捧場，多多指教。。

飛鴿傳書（IP Messenger,簡為IPMsg）是一個小巧方便的即時通信軟件，它適合用于局域網(wǎng)內(nèi)甚至廣域網(wǎng)間進行實時通信和文檔共享。特別是在局域網(wǎng)內(nèi)傳送文件/文件夾的速度非常快！

• IPMsg 是一款局域網(wǎng)內(nèi)即時通信軟件, 基于 TCP/IP(UDP).
• 可運行于多種操作平臺(Win/Mac/UNIX/Java), 并實現(xiàn)跨平臺信息交流.
• 不需要服務器支持.
• 支持文件/文件夾的傳送 (2.00版以上)
• 通訊數(shù)據(jù)采用 RSA/Blofish 加密 (2.00版以上)
• 十分小巧, 簡單易用, 而且你可以完全免費使用它
• 目前已有的版本包括: Win32, Win16, MacOS, MacOSX, X11, GTK, GNOME,Java 等, 并且公開源代碼。

1 /*==========?Constant?Value?==========*/
?2 public static final long IPMSG_COMMASK?= 0x000000ff;
?3 public static final long IPMSG_OPTMASK?= 0xffffff00;
?4 public static final long IPMSG_NOOPERATION?= 0x00000000;
?5 public static final long IPMSG_BR_ENTRY?= 0x00000001;
?6 public static final long IPMSG_BR_EXIT?= 0x00000002;
?7 public static final long IPMSG_ANSENTRY?= 0x00000003;
?8 public static final long IPMSG_BR_ABSENCE?= 0x00000004;
?9
10
11
12 public static final long IPMSG_BR_ISGETLIST?= 0x00000018;
13 public static final long IPMSG_OKGETLIST?= 0x00000015;
14 public static final long IPMSG_GETLIST?= 0x00000016;
15 public static final long IPMSG_ANSLIST?= 0x00000017;
16
17 public static final long IPMSG_SENDMSG?= 0x00000020;
18 public static final long IPMSG_RECVMSG?= 0x00000021;
19
20 public static final long IPMSG_READMSG?= 0x00000030;
21 public static final long IPMSG_DELMSG?= 0x00000031;
22
23 public static final long IPMSG_GETINFO?= 0x00000040;
24 public static final long IPMSG_SENDINFO?= 0x00000041;
25
26 //?other?opt
27 public static final long IPMSG_ABSENCEOPT?= 0x00000100;
28 public static final long IPMSG_SERVEROPT?= 0x00000200;
29 public static final long IPMSG_DIALUPOPT?= 0x00010000;
30
31 //?send?opt
32 public static final long IPMSG_SENDCHECKOPT?= 0x00000100;
33 public static final long IPMSG_SECRETOPT?= 0x00000200;
34 public static final long IPMSG_BROADCASTOPT?= 0x00000400;
35 public static final long IPMSG_MULTICASTOPT?= 0x00000800;
36 public static final long IPMSG_NOPOPUPOPT?= 0x00001000;
37 public static final long IPMSG_AUTORETOPT?= 0x00002000;
38 public static final long IPMSG_RETRYOPT?= 0x00004000;
39 public static final long IPMSG_PASSWORDOPT?= 0x00008000;
40 public static final long IPMSG_NOLOGOPT?= 0x00020000;
41 public static final long IPMSG_NEWMUTIOPT?= 0x00040000;
42
43 public static final int?MAXBUF?= 8192;
44 /*==========?end?==========*/

IPMSG收發(fā)數(shù)據(jù)包的格式（一行）：

1 version(IPMSG版本):no(消息編號，可以用系統(tǒng)時間):user(發(fā)送消息的用戶名):host(發(fā)送消息的主機名):command(上述?Command?常量，可以用?|?組合多個值):msg(消息內(nèi)容)

示例(向IPMSG發(fā)送消息，需要先打開對方的IPMSG)：

1 import java.io.IOException;
?2 import java.net.DatagramPacket;
?3 import java.net.DatagramSocket;
?4 import java.net.InetAddress;
?5 import java.net.SocketException;
?6 import java.net.UnknownHostException;
?7 import java.util.Date;
?8
?9 /**
10 ?*?@author?亂?7?8?糟?http://blog.csdn.net/comstep
11 */
12 public class?TestIPMSG
13 {
14 public static void?main(String[]?args)
15 ??{
16 ????DatagramSocket?socket;
17 ????InetAddress?address;
18
19 long IPMSG_SENDMSG?= 0x00000020;
20
21 ????String?SENDER?= "亂?7?8?糟";
22 ????String?HOST?= "Localhost";
23 ????String?MSG_CONTENT?= "Hello?World!";
24
25 try
26 ????{
27 ??????socket?= new?DatagramSocket();
28 ??????address?=?InetAddress.getByName("192.168.1.20");// 發(fā)送給消息的地址
29
30 /**
31 ???????*?IPMSG收發(fā)數(shù)據(jù)包的格式（一行）：
32 ???????*?
33 ???????*?version(IPMSG版本):no(消息編號，可以用系統(tǒng)時間):user(發(fā)送消息的用戶名):
34 ???????*?host(發(fā)送消息的主機名):command(上述?Command?常量，可以用?|?組合多個值):
35 ???????*?msg(消息內(nèi)容)
36 ???????*?
37 */
38 byte[]?buffer?=?("1:" + new?Date().getTime()?+ ":" +?SENDER?+ ":" +?HOST
39 + ":" + IPMSG_SENDMSG?+ ":" +?MSG_CONTENT).getBytes();
40
41 ??????DatagramPacket?packet?= new?DatagramPacket(buffer,?buffer.length,
42 ??????????address,?2425);
43 ??????socket.send(packet);?//?發(fā)送報文
44
45 ??????packet?= new?DatagramPacket(buffer,?buffer.length);
46 ??????socket.receive(packet);//?接收回應
47
48 ??????String?message?= new?String(packet.getData());?//?得到報文信息
49
50 ??????System.out.println(message);?//?顯示對方返回的信息
51 ????}
52 catch?(UnknownHostException?e)
53 ????{
54 ??????e.printStackTrace();
55 ????}
56 catch?(SocketException?e)
57 ????{
58 ??????e.printStackTrace();
59 ????}
60
61 catch?(IOException?e)
62 ????{
63 ??????e.printStackTrace();
64 ????}
65
66 ??}
67
68 }
69

你可以在 SourceForge 找到開源的 IP MSG for Java
http://blog.csdn.net/comstep

?

?

受http://www.oreillynet.com/onjava/blog/2007/05/javafx_first_steps_hello_onjav_1.html這篇文章的啟發(fā)，加上想學習一下JavaFX，就在上面那篇文章的基礎(chǔ)上，做了一個簡易的RSS閱讀器，其界面類似于Adobe Flex 2的一個demo：進入http://try.flex.org/index.cfm，找到Blog Reader的demo。

讀取RSS feed并沒有什么問題，使用rome：

java 代碼

1. package?rssreader; ??
3. import?com.sun.syndication.feed.synd.SyndEntry; ??
4. import?com.sun.syndication.feed.synd.SyndFeed; ??
5. import?com.sun.syndication.io.FeedException; ??
6. import?com.sun.syndication.io.SyndFeedInput; ??
7. import?com.sun.syndication.io.XmlReader; ??
8. import?java.io.IOException; ??
9. import?java.net.MalformedURLException; ??
10. import?java.net.URL; ??
12. public class?RssReader?{ ??
13. private?URL?url; ??
14. private?Integer?titleLength?=?50; ??
16. public?RssReader()?{ ??
18. ????} ??
20. public?SyndEntry[]?load(String?urlString)?throws?IllegalArgumentException,?FeedException,?IOException?{ ??
21. if?(urlString?!=?null?&&?urlString?!=?"")?{ ??
22. try?{ ??
23. ????????????????url?=?new?URL(urlString); ??
24. ????????????}?catch?(MalformedURLException?e)?{ ??
25. ????????????????e.printStackTrace(); ??
26. return null; ??
27. ????????????} ??
28. ????????} ??
29. if?(url?==?null)?{ ??
30. return null; ??
31. ????????} ??
32. ????????SyndFeedInput?input?=?new?SyndFeedInput(); ??
33. ????????SyndFeed?feed?=?input.build(new?XmlReader(url)); ??
34. ????????SyndEntry[]?entries?=?(SyndEntry[])?feed.getEntries().toArray(new?SyndEntry[0]); ??
36. for(?SyndEntry?entry?:?entries?)?{ ??
37. ????????????entry.setTitle(?entry.getTitle().length()?>?titleLength???entry.getTitle().substring(0,?titleLength?-?3?)?+?"..."?:?entry.getTitle()?); ??
38. ????????}? ??
40. return?entries; ??
41. ????} ??
44. } ??

使用JavaFX構(gòu)建UI：

JavaFX代碼

1. package?rssreader; ??
3. import?javafx.ui.*; ??
4. import?javafx.ui.canvas.*; ??
5. import?javax.swing.JComponent; ??
6. import?com.sun.syndication.feed.synd.SyndEntry; ??
8. var?reader:RssReader?=?READER; ??
10. class?RssReaderModel?{ ??
11. ????attribute?rssUrl:?String; ??
12. ????attribute?rssEntries:?SyndEntry*; ??
13. ????attribute?rssContent:?String?; ??
14. ????attribute?rssSelectedIndex:?Integer; ??
15. } ??
17. var?model?=?RssReaderModel?{ ??
18. ????rssUrl:?"http://woodstudio.javaeye.com/blog/rss_blog/alexcheng", ??
19. }; ??
22. var?panel?=?GroupPanel?{ ??
23. var?row1?=?Row?{} ??
24. var?row2?=?Row?{} ??
25. var?col?=?Column?{} ??
26. ?????rows:?[row1,?row2] ??
27. ?????columns:?col ??
28. ?????content:? ??
29. ?????????[ ??
30. ????????????GroupPanel??{ ??
31. ????????????????row:?row1 ??
32. ????????????????column:?col ??
33. var?row?=?Row?{} ??
34. var?labelCol?=??new?Column ??
35. var?urlCol?=??new?Column ??
36. var?butCol?=??new?Column ??
37. ????????????????rows:?row ??
38. ????????????????columns:?[labelCol,?urlCol,?butCol] ??
39. ????????????????content: ??
40. ????????????????[ ??
41. ????????????????????SimpleLabel?{ ??
42. ????????????????????????row:?row ??
43. ????????????????????????column:?labelCol ??
44. ????????????????????????text:?"RSS?URL:"
45. ????????????????????}, ??
46. ?????????????????????TextField?{ ??
47. ????????????????????????row:?row ??
48. ????????????????????????column:?urlCol ??
49. ????????????????????????columns:?60 ??
50. ????????????????????????value:?bind?model.rssUrl ??
51. ????????????????????}, ??
52. ????????????????????Button?{ ??
53. ????????????????????????row:?row ??
54. ????????????????????????column:?butCol ??
55. ????????????????????????text:?"Get?Entries"
56. ????????????????????????action:?operation()?{ ??
57. ????????????????????????????model.rssEntries?=?reader.load(model.rssUrl);??????????? ??
58. ????????????????????????} ??
59. ????????????????????} ??
60. ????????????????] ??
61. ????????????}, ??
62. ????????????SplitPane???{ ??
63. ????????????????row:?row2 ??
64. ????????????????column:?col ??
65. ????????????????orientation:?HORIZONTAL ??
66. ????????????????content: ??
67. ????????????????[ ??
68. ????????????????????SplitView??{ ??
69. ????????????????????????weight:?0.3 ??
70. ????????????????????????content:???? ??
71. ????????????????????????????Table?{ ??
72. ????????????????????????????????????columns: ??
73. ????????????????????????????????????[ ??
74. ????????????????????????????????????????TableColumn?{ ??
75. ????????????????????????????????????????????text:?"Title"
76. ????????????????????????????????????????}, ??
77. ????????????????????????????????????????TableColumn?{ ??
78. ????????????????????????????????????????????text:?"Date"
79. ????????????????????????????????????????}, ??
80. ????????????????????????????????????] ??
81. ????????????????????????????????????cells?:?bind?foreach?(entry?in?model.rssEntries) ??
82. ????????????????????????????????????????????[ ??
83. ????????????????????????????????????????????????TableCell?{ ??
84. ????????????????????????????????????????????????????text:?bind?entry.title ??
85. ????????????????????????????????????????????????}, ??
86. ????????????????????????????????????????????????TableCell?{ ??
87. ????????????????????????????????????????????????????text:?bind?entry.publishedDate.toLocaleString() ??
88. ????????????????????????????????????????????????} ??
89. ????????????????????????????????????????????] ??
90. ????????????????????????????????????selection:?bind?model.rssSelectedIndex ??
91. ????????????????????????????????}??? ??
92. ????????????????????}, ??
93. ????????????????????SplitView??{ ??
94. ????????????????????????weight:?0.7 ??
95. ????????????????????????content: ??
96. ????????????????????????????EditorPane???{ ??
97. ????????????????????????????????opaque:?true
98. ????????????????????????????????contentType:?HTML ??
99. ????????????????????????????????editable:?false
100. ????????????????????????????????text:?bind?model.rssContent ??
101. ????????????????????????????} ??
102. ????????????????????????} ??
103. ????????????????] ??
104. ????????????} ??
105. ?????????]? ??
106. }; ??
108. trigger?on?(RssReaderModel.rssSelectedIndex?=?value)?{ ??
109. var?desc?=?rssEntries[value].description.value; ??
110. ????rssContent?=?"?{desc}?";? ??
111. } ??
113. MY_CONTAINER:JComponent.add(panel.getComponent()); ??

接著就是使用JSR223的scripting framework來執(zhí)行：

java 代碼

1. package?rssreader; ??
3. import?javax.script.Bindings; ??
4. import?javax.script.ScriptContext; ??
5. import?javax.script.ScriptEngine; ??
6. import?javax.script.ScriptEngineManager; ??
7. import?javax.script.SimpleScriptContext; ??
8. import?javax.swing.JFrame; ??
10. public class?Main?{ ??
12. /**
13. ?????*?@param?args
14. ?????*?@throws?Exception
15. ?????*/
16. public static void?main(String[]?args)?throws?Exception?{ ??
17. ????????RssReader?reader?=?new?RssReader(); ??
19. ????????JFrame?frame?=?new?JFrame( ??
20. "RSS?Reader?implemented?using?JavaFX?by?alexcheng"); ??
21. ????????frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); ??
22. ????????frame.setSize(800,?600); ??
24. ????????ClassLoader?loader?=?Thread.currentThread().getContextClassLoader(); ??
25. ????????ScriptEngineManager?manager?=?new?ScriptEngineManager(loader); ??
26. ????????ScriptEngine?engine?=?manager.getEngineByExtension("fx"); ??
28. ????????Bindings?bindings?=?engine.createBindings(); ??
29. ????????bindings.put("READER:rssreader.RssReader",?reader); ??
31. ????????bindings.put("MY_CONTAINER:javax.swing.JComponent",?frame ??
32. ????????????????.getContentPane()); ??
34. ????????ScriptContext?context?=?new?SimpleScriptContext(); ??
35. ????????context.setBindings(bindings,?ScriptContext.GLOBAL_SCOPE); ??
36. ????????context.setBindings(bindings,?ScriptContext.ENGINE_SCOPE); ??
37. ????????engine.setContext(context); ??
39. ????????String?script?=?"import?rssreader.FxMain;"; ??
40. ????????engine.eval(script); ??
42. ????????frame.setVisible(true); ??
43. ????} ??
45. } ??

最后的界面如下：

javafxrssreader.JPG

?描述:
?JavaFX RSS Reader

?文件大小:
?74 KB

?看過的:
?文件被下載或查看 28 次

1。 Release Test
　　Purpose:
　　測試手機的基本功能是否實現(xiàn)，是否有進一步測試的必要性
　　Attention:
　　Release Test的Test Case具有一定的典型性，主要是反映手機最基本功能的Test Case
　　本類測試只需要依據(jù)Test Case進行測試，不需要進一步發(fā)揮
　　如果有發(fā)現(xiàn)與Case無關(guān)的Error, 在測試通過后才可以填報Error Report
　　此類測試有一門檻值，即Test Case的Pass率達到一定值（如95%）才能宣布版本發(fā)布成功，進入進一步的測試，否則此版本無效。
　　除了門檻值外，如果重要功能模塊的Test Case沒通過，也會終止這個版本。
　　2 System Test
　　Full Round System Test
　　Purpose
　　對手機的所有功能進行全面的測試(所有語言包)
　　由于Case不可能包含所有方面，所以測試時應適度發(fā)揮，盡力完成全面測試
　　Common System Test (Medium or Minor)
　　Attention:
　　System Test一般分為兩個部分，“跑Case”和Free Test。
　　在測試初期，一般只需要按照Test Case測，把一些不可重現(xiàn)的Error都記錄下來。同時遇到Test Case的問題或者不充分，應該立即解決（和Team Leader或者Special List討論，補寫Test Case）。在這一階段結(jié)束后，一般要寫一個Summary Report。把這一階段的測試結(jié)果和遇到的問題、自己的見解都寫在里面（當然是用English）。
　　當所有Test Case都測完后，就進入Free Test期間。這里的Free Test具有明確的目的性和范圍。一般來說，這段時間的Free Test只需要測自己負責的模塊。而且Free Test還負責重現(xiàn)前期“跑Case”是遺留的不可重現(xiàn)的Error。
　　3 Focus Test
　　Purpose:
　　集中于一個或幾個點進行測試(同System Test)

　　4 Stress Test
　　Purpose:
　　為了解決市場上發(fā)現(xiàn)的重大Error，而進行的有針對性的強度測試
　　主要是利用邊緣測試（臨界測試）手段
　　Attention:
　　壓力測試，顧名思義，是給手機施加一定壓力，從而找出手機軟件上的Error。一般來說，對手機施加的壓力主要有：
　　存儲壓力：由于手機采用的是棧式存儲，所以當一個存儲塊滿了之后，如果程序員不做相應處理或者處理不好的話，很容易造成其他存儲區(qū)被擦除，從而在UI上出現(xiàn)問題（其他功能無法正常使用）。
　　邊界壓力：邊界一直是程序員最容易忽略的地方。
　　響應能力壓力：有時候某個操作可能處理的時間很長，在處理期間如果測試者再不斷地進行其他操作的話，很容易出現(xiàn)問題。
　　網(wǎng)絡(luò)流量壓力（如在接電話時進行短信服務）等等。
　　在項目中，Stress Test有時也會用來重現(xiàn)不可重現(xiàn)的Error。
　　由于有不少不可重現(xiàn)的Error是由于Memory Leak(內(nèi)存泄漏)引起的，所以不停的重復同一個操作是重現(xiàn)一個不可重現(xiàn)的Error的一個好方法。
　　5 Free Test

JavaFX Script? （下文中成為JavaFX）語言是一種聲明式的靜態(tài)類型編程語言。它具有第一級函數(shù)（first-class functions）、聲明式的語法、列表推導（list-comprehensions）及基于依賴關(guān)系的增量式求值（incremental dependency-based evaluation）等特征。JavaFX 腳本式語言特別適用于Java2D swing GUI組件，它允許簡單地創(chuàng)建圖形界面。

譯者注：第一級函數(shù)指函數(shù)被當作對象對待，可以在運行時賦值、傳遞和返回。詳見wikipedia上的解釋。

譯者注：列表推導指一種在函數(shù)語言中的表達式，它表示了在一個或者多個列表的成員（被選擇的）進行某種操作的結(jié)果。它被稱為“syntactic sugar”，即為開發(fā)者提供了便捷的多種函數(shù)的應用組合。詳見FOLDC對list comprehension的解釋。

本文檔給出了JavaFX 腳本式編程語言的非正式描述。

就語言方面來說，出現(xiàn)了Java FX script 項目。Java FX是很靈巧的，它提供了一個高級的腳本接口，運行在Java 2D的API上。從用戶的角度來看，他們不需要編寫Java代碼，不需要深入理解復雜的線程，Java 2D，Swing類的層次結(jié)構(gòu)，定時框架結(jié)構(gòu)（timing framework）等等。相反，他們只是編寫腳本語言和描繪出所需要的GUI，包括活波的音響效果，圖形效果，比如說梯度或者音樂，和數(shù)據(jù)綁定等等，這些都建立在一個基礎(chǔ)API上。
??? 這里有許多的工具幫助你學習syntax語言，相關(guān)資源這個從這個網(wǎng)站獲得；Java FX研發(fā)小組的目標就是提供syntax語言，和一些關(guān)于Java FX的用戶體驗，這些用戶包括美術(shù)設(shè)計員和那些對應用程序可視界面美觀感興趣的民眾。當前，Java FX某種程度上作為第四步產(chǎn)生的語言在運行，因為首先是解釋器將FX腳本創(chuàng)建成為Java代碼，然后再調(diào)用適當?shù)腏ava 2D API。該小組長期的目標是將FX腳本直接編譯成字節(jié)碼。
??? Java FX添加到桌面Java是一件非常好的事情，但是，這得取決于是否有這樣的一種JRE的存在，它能運行Java FX生成的代碼。有些人認為FX已經(jīng)進軍到RIA(rich Internet application)領(lǐng)域，和Adobe公司的 Flex一較高下。但是，目前還是有一些難題需要解決，舉個例子，如何才能讓桌面Java的安裝體驗和運行時間性能比得上其它的RIA框架。還好，這種問題正在被其他的項目解決，這個項目名稱就是Java kernel。
??? Java kernel主動承認這么一個事情，即大多數(shù)的Java應用程序都是只有JRE的部分大小，如Limewire（一個文件共享的桌面應用程序），它只有JRE的三分之一大小。Kernel將會對JRE重新打包，使得只下載應用程序所需要的部分JRE。每個程序所需要的基本部分將會被下載，作為JRE啟動所需要的最小部分，其他的部分根據(jù)需要下載，或者根據(jù)ClassNotFound異常信息，下載缺失的類。這將是一個巨大的好消息幫助桌面Java應用程序瘦身，同時還能使得桌面Java應用程序執(zhí)行的更為有效。除了解決如何下載的問題外，kernel還非常關(guān)注Java程序的啟動性能。
??? 在先前的kernel幾個版本，熱啟動時間（warm start times）減少了很多，但是，在應用程序調(diào)用main(String[])前，冷啟動JRE仍然需要延誤許多秒的時間。Java kernel正在嘗試有效的處理冷啟動，將冷啟動轉(zhuǎn)變?yōu)闊釂樱ㄟ^一些相關(guān)的技術(shù)，如預加載（pre-loading）JRE，從硬盤讀入到內(nèi)存，還有一個操作系統(tǒng)服務，這個服務的功能就是監(jiān)視可分配的內(nèi)存來加載JRE，使得用戶獲得最佳的性能。出了這些，kernel還提供了一個新的瀏覽器插件，提供給Web 開發(fā)者更多的關(guān)于桌面運行信息，可獲得的JRE水平等等。
???? 對于桌面Java來說，Java kernel 和Java FX兩大好消息。說Kernel是一個非常好的技術(shù)，是因為它承認了Swing已經(jīng)到了一個非常成熟的階段，并且?guī)椭_發(fā)這如何將他們的Java應用程序更為快速，更為有效的搬到用戶桌面上。說FX是兩外一個非常好的消息，是因為它為Java開發(fā)者打開了新篇章，特別是那些愿意使用腳本語言和做一些高級的，活波的，圖形效果的開發(fā)者，他們只需要寫簡單幾行代碼就可以完成。我相信這兩項技術(shù)將會使得更多的應用程序用Java語言編寫，運行在用戶的機器上，同時，對于用戶和開發(fā)者來說，應用程序變得更快，更簡單。

相關(guān)學習資料

https://openjfx.dev.java.net/JavaFX_Programming_Language_CN.html

https://openjfx.dev.java.net/JavaFX_Programming_Language.html

https://openjfx.dev.java.net/Getting_Started_With_JavaFX.html

https://openjfx.dev.java.net/