How many bytes does Boolean occupy?

I met a question about boolean The problem of occupying a few bytes , With questions , Search the Internet , There are many answers , stay Java Of the eight basic data types defined in , Except that the other seven types have a clear number of bytes of memory , Just boolean The type does not give a specific number of occupied bytes .

according to http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html Description of official documents ：

• 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.

• 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.

• int: By default, the int data type is a 32-bit signed two's complement integer, which has a minimum value of -231 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 232-1. 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.

• 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.

• 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.

• 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.

• 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.( Boolean data types have only two possible values ：true and false. Use this data type to track true / Simple sign of false condition . This data type represents a bit of information , But it's “ size ” Not precisely defined .)

• 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).

1、1 individual bit

The reason is that boolean The value of type is only true and false Two logical values , It will be used after compilation 1 and 0 To express , These two numbers only need... In memory 1 position （bit） You can store , Bit is the smallest storage unit of a computer .

2、1 Bytes

The reason is that although compiled 1 and 0 Just occupy 1 Bitspace , But the smallest unit of data processed by a computer is 1 Bytes ,1 Bytes are equal to 8 position , The actual storage space is ： use 1 The lowest byte of storage , other 7 Bit use 0 fill , If the value is true The stored binary is ：0000 0001, If it is false The stored binary is ：0000 0000.

3、4 Bytes

The reason source is 《Java Virtual machine specification 》 Description in a Book ：“ Although the definition of boolean This data type , But only very limited support for it . stay Java There is nothing in the virtual machine for boolean Value specific bytecode instructions ,Java Language expressions operate on boolean value , Use... After compilation Java In the virtual machine int Data type instead of , and boolean The array will be encoded as Java The virtual machine byte Array , Every element boolean Elements take up 8 position ”. So we can get boolean The type occupied by the single use is 4 Bytes , In the array is again 1 Bytes .

summary

stay 《Java Virtual machine specification 》 A single boolean Occupy 4 Bytes , and boolean Array 1 Definition of bytes , Specifically   still more See whether the virtual machine implementation is in accordance with the specification , therefore 1 Bytes 、4 Every byte is possible .