afreechart/src/main/java/org/afree/data/category/DefaultCategoryDataset.java
/**
     * Adds the specified value to an existing value in the dataset (if the
     * existing value is <code>null</code>, it is treated as if it were 0.0).
     * 
     * @param value
     *            the value.
     * @param rowKey
     *            the row key (<code>null</code> not permitted).
     * @param columnKey
     *            the column key (<code>null</code> not permitted).
     * 
     * @throws UnknownKeyException
     *             if either key is not defined in the dataset.
     */
Adds the specified value to an existing value in the dataset (if the
existing value is null, it is treated as if it were 0.0).

@param value
the value.
@param rowKey
the row key (null not permitted).
@param columnKey
the column key (null not permitted).

@throws UnknownKeyException
if either key is not defined in the dataset.
Adds the specified value to an existing value in the dataset ( if the existing value is null it is treated as if it were 0 . 0 ) . @param value the value . @param rowKey the row key ( null not permitted ) . @param columnKey the column key ( null not permitted ) . @throws UnknownKeyException if either key is not defined in the dataset .
public void incrementValue(double value, Comparable rowKey,
            Comparable columnKey) {
        double existing = 0.0;
        Number n = getValue(rowKey, columnKey);
        if (n != null) {
            existing = n.doubleValue();
        }
        setValue(existing + value, rowKey, columnKey);
    }
public void incrementValue ( double value , Comparable rowKey , Comparable columnKey ) { double existing = 0.0 ; Number n = getValue ( rowKey , columnKey ) ; if ( n != null ) { existing = n . doubleValue ( ) ; } setValue ( existing + value , rowKey , columnKey ) ; }
Adds the specified value to an existing value in the dataset (if the
 existing value is <code>null</code>, it is treated as if it were 0.0).
Adds the specified value to an existing value in the dataset ( if the existing value is <code > null< / code > it is treated as if it were 0 . 0 ) .