How many bytes does the boolean type occupy in Java?

The boolean type in Java occupies bytes: 1. 1 bit. The reason is that the value of the boolean type only has two logical values: true and false. After compilation, it will be represented by 1 and 0; 2. 1 Bytes, the reason is that although 1 and 0 only occupy 1 bit of space after compilation, the smallest unit of data processed by the computer is 1 byte.

Why do you want to ask this question? First of all, among the eight basic data types defined in Java, except for the other seven types, there are clear memory occupied bytes. In addition, the specific number of bytes occupied by the boolean type is not given, because the boolean type does not exist for the virtual machine. The boolean type will be represented by other data types after compilation. How many bytes does the boolean type occupy? byte? With doubts, I searched online and found various answers. Basically, they are as follows:

1. 1 bit

The reason is that the boolean type value only has two logical values: true and false. After compilation, they will be represented by 1 and 0. These two numbers only require 1 bit (bit) to be stored in the memory. A bit is the smallest storage unit of a computer.

2. 1 byte

The reason is that although 1 and 0 only occupy 1 bit of space after compilation, the smallest unit for computer processing data is 1 byte, 1 byte Equal to 8 bits, the actual storage space is: use the lowest bit of 1 byte to store, and fill the other 7 bits with 0. 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 comes from the description in the "Java Virtual Machine Specification": "Although the boolean data type is defined, only very Limited support. There are no bytecode instructions dedicated to boolean values ​​in the Java virtual machine. The boolean values ​​operated by Java language expressions are replaced by the int data type in the Java virtual machine after compilation, and boolean arrays It will be encoded into a byte array of the Java virtual machine, and each boolean element occupies 8 bits." In this way, we can conclude that the boolean type occupies 4 bytes when used alone, and 1 byte in the array.

Obviously the third one is a more accurate statement, so why does the virtual machine use int instead of boolean? Why not use byte or short? Wouldn't it save more memory space? Most people will naturally think like this. I also have this question. After checking the information, I found that the reason for using int is that for the current 32-bit processor (CPU), the data processed at one time is 32 bits (not here) It refers to 32/64-bit systems, but refers to the CPU hardware level), which has the characteristics of efficient access.

Final summary:

According to the description of the official document at http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html:

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 type: The Boolean data type has only two possible values: true and false. Use this data type for simple markers that track true/false conditions. This data type represents this bit of information, but its "size" is not precisely defined.

It can be seen that the boolean type does not give a precise definition. The "Java Virtual Machine Specification" gives the definition of 4 bytes and 1 byte of the boolean array. The specifics depend on the virtual machine implementation. Whether it follows the specification, so 1 byte or 4 bytes are possible. This is actually a game between computing efficiency and storage space, both of which are very important.

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