Module org.hdfgroup.object
Package hdf.object.h5

Class H5Attribute

Object
hdf.object.HObject
hdf.object.Dataset
hdf.object.Attribute
hdf.object.h5.H5Attribute
All Implemented Interfaces:
CompoundDataFormat, DataFormat, MetaDataContainer, Serializable
public class H5Attribute
extends Attribute
An attribute is a (name, value) pair of metadata attached to a primary data object such as a dataset, group or named datatype.

Like a dataset, an attribute has a name, datatype and dataspace.

For more details on attributes, HDF5 User's Guide

The following code is an example of an attribute with 1D integer array of two elements. 

 // Example of creating a new attribute
 // The name of the new attribute
 String name = "Data range";
 // Creating an unsigned 1-byte integer datatype
 Datatype type = new Datatype(Datatype.CLASS_INTEGER, // class
                              1,                      // size in bytes
                              Datatype.ORDER_LE,      // byte order
                              Datatype.SIGN_NONE);    // unsigned
 // 1-D array of size two
 long[] dims = {2};
 // The value of the attribute
 int[] value = {0, 255};
 // Create a new attribute
 Attribute dataRange = new Attribute(name, type, dims);
 // Set the attribute value
 dataRange.setValue(value);
 // See FileFormat.writeAttribute() for how to attach an attribute to an object,
 @see hdf.object.FileFormat#writeAttribute(HObject, Attribute, boolean)
For an atomic datatype, the value of an Attribute will be a 1D array of integers, floats and strings. For a compound datatype, it will be a 1D array of strings with field members separated by a comma. For example, "{0, 10.5}, {255, 20.0}, {512, 30.0}" is a compound attribute of {int, float} of three data points.
Version:
2.0 4/2/2018
Author:
Peter X. Cao, Jordan T. Henderson
See Also:
Datatype, Serialized Form

  • Constructor Details

    • H5Attribute

      public H5Attribute​(HObject parentObj, String attrName, Datatype attrType, long[] attrDims)
      Create an attribute with specified name, data type and dimension sizes. For scalar attribute, the dimension size can be either an array of size one or null, and the rank can be either 1 or zero. Attribute is a general class and is independent of file format, e.g., the implementation of attribute applies to both HDF4 and HDF5.

      The following example creates a string attribute with the name "CLASS" and value "IMAGE". 

       long[] attrDims = { 1 };
 String attrName = "CLASS";
 String[] classValue = { "IMAGE" };
 Datatype attrType = null;
 try {
     attrType = new H5Datatype(Datatype.CLASS_STRING, classValue[0].length() + 1, Datatype.NATIVE, Datatype.NATIVE);
 }
 catch (Exception ex) {}
 Attribute attr = new Attribute(attrName, attrType, attrDims);
 attr.setValue(classValue);
      Parameters:
      parentObj - the HObject to which this Attribute is attached.
      attrName - the name of the attribute.
      attrType - the datatype of the attribute.
      attrDims - the dimension sizes of the attribute, null for scalar attribute
      See Also:
      Datatype

    • H5Attribute

      public H5Attribute​(HObject parentObj, String attrName, Datatype attrType, long[] attrDims, Object attrValue)
      Create an attribute with specific name and value. For scalar attribute, the dimension size can be either an array of size one or null, and the rank can be either 1 or zero. Attribute is a general class and is independent of file format, e.g., the implementation of attribute applies to both HDF4 and HDF5.

      The following example creates a string attribute with the name "CLASS" and value "IMAGE". 

       long[] attrDims = { 1 };
 String attrName = "CLASS";
 String[] classValue = { "IMAGE" };
 Datatype attrType = null;
 try {
     attrType = new H5Datatype(Datatype.CLASS_STRING, classValue[0].length() + 1, Datatype.NATIVE, Datatype.NATIVE);
 }
 catch (Exception ex) {}
 Attribute attr = new Attribute(attrName, attrType, attrDims, classValue);
      Parameters:
      parentObj - the HObject to which this Attribute is attached.
      attrName - the name of the attribute.
      attrType - the datatype of the attribute.
      attrDims - the dimension sizes of the attribute, null for scalar attribute
      attrValue - the value of the attribute, null if no value
      See Also:
      Datatype

  • Method Details

    • open

      public long open()
      Description copied from class: HObject
      Opens an existing object such as a dataset or group for access. The return value is an object identifier obtained by implementing classes such as H5.H5Dopen(). This function is needed to allow other objects to be able to access the object. For instance, H5File class uses the open() function to obtain object identifier for copyAttributes(long src_id, long dst_id) and other purposes. The open() function should be used in pair with close(long) function.
      Overrides:
      open in class Attribute
      Returns:
      the object identifier if successful; otherwise returns a negative value.
      See Also:
      HObject.close(long)

    • close

      public void close​(long aid)
      Description copied from class: HObject
      Closes access to the object.

      Sub-classes must implement this interface because different data objects have their own ways of how the data resources are closed.

      For example, H5Group.close() calls the hdf.hdf5lib.H5.H5Gclose() method and closes the group resource specified by the group id.

      Overrides:
      close in class Attribute
      Parameters:
      aid - The object identifier.

    • init

      public void init()
      Specified by:
      init in interface DataFormat
      Overrides:
      init in class Attribute

    • convertCompoundByteMember

      protected Object convertCompoundByteMember​(byte[] data, long data_type, long start, long len)
      Given an array of bytes representing a compound Datatype and a start index and length, converts len number of bytes into the correct Object type and returns it.
      Overrides:
      convertCompoundByteMember in class Attribute
      Parameters:
      data - The byte array representing the data of the compound Datatype
      data_type - The type of data to convert the bytes to
      start - The start index of the bytes to get
      len - The number of bytes to convert
      Returns:
      The converted type of the bytes