Shulou(Shulou.com)06/01 Report--

This article shows you what data types are in Hadoop, which are concise and easy to understand, which will definitely brighten your eyes. I hope you can get something through the detailed introduction of this article.

one。 Hadoop built-in data types

BooleanWritable: standard Boolean value

ByteWritable: single byte value

DoubleWritable: double byte numeric

FloatWritable: floating point number

IntWritable: integer number

LongWritable: number of long integers

Text: text stored in UTF8 format

NullWritable: used when key or value is empty

All the data types in Hadoop implement the Writable interface so that the data defined with these types can be transferred over the network and stored in files.

two。 Implementation of user-defined data types

1. Inherit the interface Writable and implement its methods write () and readFields () so that the data can be serialized to complete network transfer or file input / output

two。 If this data needs to be used as a primary key key, or when you need to compare numeric values, you need to implement the WritalbeComparable interface and implement its methods write (), readFields (), CompareTo ().

3. Data type, there must be a no-parameter constructor, to facilitate reflection, to create objects.

4. In custom data types, it is recommended to use java's native data types, and it is best not to use Hadoop data types that encapsulate native types. Eg.int x; / / IntWritable String s; / / Text

Public class Point3D implements WritableComparable

{

Private float x,y,z

Public float getX () {return x;}

Public float getY () {return y;}

Public float getZ () {return z;}

Public Point3D () {}

Public void readFields (DataInput in) throws IOException

{

X = in.readFloat ()

Y = in.readFloat ()

Z = in.readFloat ()

}

Public void write (DataOutput out) throws IOException

{

Out.writeFloat (x)

Out.writeFloat (y)

Out.writeFloat (z)

}

Public int CompareTo (Point3D p)

{

/ / the specific implementation compares the size of the current coordinate point this (x _ journal y ~ z) with the specified point p (x _ journal y _ z).

/ and output:-1 (less than), 0 (equal to), 1 (greater than)

}

}

What are the data types in Hadoop? have you learned any knowledge or skills? If you want to learn more skills or enrich your knowledge reserve, you are welcome to follow the industry information channel.

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