Writable type of Hadoop comes with

In Hadoop, there is no basic type class (Integer, float, etc.) that comes with Java, but instead uses the classes that you have developed. Hadoop comes with a number of serialization types, roughly divided into the following two categories:

• Classes that implement the Writablecomparable interface

Base: booleanwritable | Bytewritable

Numbers: intwritable | vintwritable | floatwritable | longwritable | vlongwritable | Doublewritable

Advanced: nullwritable | Text | byteswritable | Mdshash | objectwritable | Genericwritable

• Classes that implement only the writable interface

Array: arraywritable | Twodarraywritable

Mapping: abstractmapwritable | mapwritable | Sortedmapwritable

To facilitate understanding of the writable types that Hadoop comes with, we use the following table to demonstrate the correspondence between Java primitives and writable

Ja VA basic type	writable implementation	strong> bytes
Boolean	booleanwritable	1 / td>
Byte	bytewritable	1
I NT	intwritable	4
Float	Floatwri Table	4
Long	longwritable	8
Double	doublewritable	8

for the writable types in Hadoop above, we'll just briefly introduce Text. The Text class is a writable type in the UTF-8 format. It can be understood as a type of writable similar to java.lang.String. Text uses the int type to store the number of bytes in the character encoding, and the maximum value is 2GB. It has a find () method, equivalent to the IndexOf () method in Java's String. The Text instance is reused primarily through the set (byte[] utf8) method, as follows

Text text = new text ("Hadoop");//Construct a text object

Text.set ("AutoNavi");//re-assign value

Writable type of Hadoop comes with