## ncsa.hdf.object
Class Attribute

    java.lang.Object
      ncsa.hdf.object.Attribute

All Implemented Interfaces:
  java.io.Serializable, Metadata

    public class Attribute

extends java.lang.Object
implements Metadata

An attribute is a (name, value) pair of metadata attached to a primary data object such as dataset, group or named datatype.

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

For more details on attibutes, see HDF5 User's Guide

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

     // Example of creatinge 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);    // signed or 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,

    Version:
      1.1 9/4/2007
    Author:
      Peter X. Cao
    See Also:

, `Datatype`, Serialized Form

Field Summary
`protected boolean` `isScalar` flag to indicate if the dataset is a single scalar point

Constructor Summary
`Attribute(java.lang.String attrName, Datatype attrType, long[] attrDims)` Create an attribute with specified name, data type and dimension sizes.
`Attribute(java.lang.String attrName, Datatype attrType, long[] attrDims, java.lang.Object attrValue)` Create an attribute with specific name and value.

Method Summary
`long[]` `getDataDims()` Returns the dimension sizes of the data value of the attribute.
`java.lang.String` `getName()` Returns the name of the attribute.
`int` `getRank()` Returns the rank (number of dimensions) of the attribute.
`Datatype` `getType()` Returns the datatype of the attribute.
`java.lang.Object` `getValue()` Returns the value of the attribute.
`boolean` `isScalar()`
`boolean` `isUnsigned()` Checks if the data type of this attribute is an unsigned integer.
`void` `setValue(java.lang.Object theValue)` Sets the value of the attribute.
`java.lang.String` `toString()` Return the name of the attribute.
`java.lang.String` `toString(java.lang.String delimiter)` Returns a string representation of the data value of the attribute.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

Field Detail

### isScalar

    protected boolean isScalar

  flag to indicate if the dataset is a single scalar point

Constructor Detail

### Attribute

    public Attribute(java.lang.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 = new H5Datatype(Datatype.CLASS_STRING, classValue[0]
               .length() + 1, -1, -1);
       Attribute attr = new Attribute(attrName, attrType, attrDims);
       attr.setValue(classValue);

  Parameters:
    `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`

### Attribute

    public Attribute(java.lang.String attrName,
                     Datatype attrType,
                     long[] attrDims,
                     java.lang.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 = new H5Datatype(Datatype.CLASS_STRING, classValue[0]
               .length() + 1, -1, -1);
       Attribute attr = new Attribute(attrName, attrType, attrDims, classValue);

  Parameters:
    `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 Detail

### getValue

    public java.lang.Object getValue()

  Returns the value of the attribute. For atomic datatype, this will be an 1D array of integers, floats and strings. For compound datatype, it will be an 1D array of strings with field members separated by comma. For example, "{0, 10.5}, {255, 20.0}, {512, 30.0}" is a cmpound attribute of {int, float} of three data points.

  Specified by:
    `getValue` in interface `Metadata`
  Returns:
    the value of the attribute, or null if failed to retrieve data from file.

### setValue

    public void setValue(java.lang.Object theValue)

  Sets the value of the attribute. It returns null if failed to retrieve the name from file.

  Specified by:
    `setValue` in interface `Metadata`
  Parameters:
    `theValue` - The value of the attribute to set

### getName

    public java.lang.String getName()

  Returns the name of the attribute.

  Returns:
    the name of the attribute.

### getRank

    public int getRank()

  Returns the rank (number of dimensions) of the attribute. It returns a negative number if failed to retrieve the dimension information from file.

  Returns:
    the number of dimensions of the attribute.

### getDataDims

    public long[] getDataDims()

  Returns the dimension sizes of the data value of the attribute. It returns null if failed to retrieve the dimension information from file.

  Returns:
    the dimension sizes of the attribute.

### getType

    public Datatype getType()

  Returns the datatype of the attribute. It returns null if failed to retrieve the datatype information from file.

  Returns:
    the datatype of the attribute.

### isScalar

    public boolean isScalar()

  Returns:
    true if the data is a single scalar point; otherwise, returns false.

### isUnsigned

    public boolean isUnsigned()

  Checks if the data type of this attribute is an unsigned integer.

  Returns:
    true if the data type of the attribute is an unsigned integer; otherwise returns false.

### toString

    public java.lang.String toString()

  Return the name of the attribute.

  Overrides:
    `toString` in class `java.lang.Object`
  See Also:
    `toString(String delimiter)`

### toString

    public java.lang.String toString(java.lang.String delimiter)

  Returns a string representation of the data value of the attribute. For example, "0, 255".

  For compound datatype, it will be an 1D array of strings with field members separated by comma. For example, "{0, 10.5}, {255, 20.0}, {512, 30.0}" is a cmpound attribute of {int, float} of three data points.

  Parameters:
    `delimiter` - The delimiter to separate individual data point. It can be comma, semicolon, tab or space. For example, to String(",") will separate data by comma.
  Returns:
    the string representation of the data values.