Java Primitive Data Types (interview 竟然有問!!!)

boolean

1-bit. May take on the values true and false only.

true and false are defined constants of the language and are not the same as True and False, TRUE and FALSE, zero and nonzero, 1 and 0 or any other numeric value. Booleans may not be cast into any other type of variable nor may any other variable be cast into a boolean.

byte

1 signed byte (two's complement). Covers values from -128 to 127.

short

2 bytes, signed (two's complement), -32,768 to 32,767

int

4 bytes, signed (two's complement). -2,147,483,648 to 2,147,483,647. Like all numeric types ints may be cast into other numeric types (byte, short, long, float, double). When lossy casts are done (e.g. int to byte) the conversion is done modulo the length of the smaller type.

long

8 bytes signed (two's complement). Ranges from -9,223,372,036,854,775,808 to +9,223,372,036,854,775,807.

float

4 bytes, IEEE 754. Covers a range from 1.40129846432481707e-45 to 3.40282346638528860e+38 (positive or negative).

Like all numeric types floats may be cast into other numeric types (byte, short, long, int, double). When lossy casts to integer types are done (e.g. float to short) the fractional part is truncated and the conversion is done modulo the length of the smaller type.

double

8 bytes IEEE 754. Covers a range from 4.94065645841246544e-324d to 1.79769313486231570e+308d (positive or negative).

char

2 bytes, unsigned, Unicode, 0 to 65,535

Chars are not the same as bytes, ints, shorts or Strings.

資料型別可以分基本資料型別以及使用者自訂型別。

基本資料型別java 內定有8種基本型別。

有整數類 : byte, short , int , long . 資料長度為 8-bits,16-bits,32-bits,64-bits。

浮點數類: double , float. 資料長度為32-bits,64bits

文字類: char資料長度為2bytes且為Unicode`.

邏輯類: boolean .

這8種基本型別有各自的固定記憶體長度跟資料格式。