八種資料型別

tip:八種類型我是這樣記憶的：boolean,char是我們常用的，double是雙

精度浮點小數，有雙就有單 : float是單精度浮點小數,int是一個座標，short比int短，long比int長，byte是整數的最小單位.

以下是官方文件，我翻譯一下。（重點在於boolean值的描述）

• byte: The byte data type is an 8-bit signed two's complement integer. It has a minimum value of -128 and a maximum value of 127 (inclusive). The byte data type can be useful for saving memory in large

  arrays, where the memory savings actually matters. They can also be used in place of int where their limits help to clarify your code; the fact that a variable's range is limited can serve as a form of documentation.

        byte資料型別是一個8-bit有符號的二進位制補碼整數。取值範圍：【-128，127】，當記憶體比較重要的時候：比如超大陣列的情況。

• short

  : The short data type is a 16-bit signed two's complement integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive). As with byte, the same guidelines apply: you can use a short to save memory in large arrays, in situations where the memory savings actually matters.

      short是一個16-bit 的二進位制補碼整數，取值範圍：[-32768,32767]。同上文byte.

• int: By default, the int data type is a 32-bit signed two's complement integer, which has a minimum value of -2*31 and a maximum value of 231-1.   In Java SE 8 and later, you can use the int data type to represent an unsigned 32-bit integer, which has a minimum value of 0 and a maximum value of 2*32-1. Use the Integer class to use int data type as an unsigned integer. See the section The Number Classes for more information. Static methods like compareUnsigned, divideUnsigned etc have been added to the Integer class to support the arithmetic operations for unsigned integers.

      預設情況下，int是32-bit的二進位制補碼整數，取值範圍是:[-2^31,2^31-1]，在JavaSE8以後，你可以使用int資料型別去展現一個無符號為的32-bit的值(取值範圍：[0,2^32 - 1]),使用Integer類去操作無符號為的Integer，具體情況請參考Number類。包含compareUnsigned, divideUnsigned等靜態方法.

• long: The long data type is a 64-bit two's complement integer. The signed long has a minimum value of -263 and a maximum value of 263-1. In Java SE 8 and later, you can use the long data type to represent an unsigned 64-bit long, which has a minimum value of 0 and a maximum value of 264-1. Use this data type when you need a range of values wider than those provided by int. The Long class also contains methods like compareUnsigned, divideUnsigned etc to support arithmetic operations for unsigned long.

        幾乎同int，除了不包含compareUnsigned, divideUnsigned等靜態方法。

• float: The float data type is a single-precision 32-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the Floating-Point Types, Formats, and Values section of the Java Language Specification. As with the recommendations for byte and short, use a float (instead of double) if you need to save memory in large arrays of floating point numbers. This data type should never be used for precise values, such as currency. For that, you will need to use the java.math.BigDecimal class instead. Numbers and Strings covers BigDecimal and other useful classes provided by the Java platform.

       float是單精度的浮點小數.存在的意義類似於short，省記憶體.

• double: The double data type is a double-precision 64-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the Floating-Point Types, Formats, and Values section of the Java Language Specification. For decimal values, this data type is generally the default choice. As mentioned above, this data type should never be used for precise values, such as currency.

     double是我們在十進位制小數情況下的預設選擇，但是注意，不要把他當做通用的類.

• boolean: The boolean data type has only two possible values: true and false. Use this data type for simple flags that track true/false conditions. This data type represents one bit of information, but its "size" isn't something that's precisely defined.

         注意：boolean的記憶體大小是和JVM有關的。布林值不能與整型值相互轉換

• char: The char data type is a single 16-bit Unicode character. It has a minimum value of '\u0000' (or 0) and a maximum value of '\uffff' (or 65,535 inclusive).,四個位元組.

        char四個位元組.

額外說一句：“我們強烈建議不要再程式中使用char型別，除非確定需要處理UTF-16程式碼單元，最好將字串作為抽象資料型別處理”.------《Java核心技術卷 卷1》p35

最後：Java沒有任何無符號(unsigned)形式的int,long,short或byte型別.