Jakarta Commons Cookbook

5.21. Retrieving Map Values Without Casting

Problem

You need to retrieve a primitive double from a Map, but the value is stored as a Double object.

Solution

Use MapUtils.getDoubleValue() to retrieve a Double object from a Map as a double primitive. The following example demonstrates getDoubleValue( ):

import java.util.*;
import org.apache.commons.lang.ArrayUtils;
import org.apache.commons.collections.MapUtils;

Object[] mapArray = new Object[][] {
    { "A", new Double( 2.0 ) },
    { "B", new Double( 0.223242 ) },
    { "C", new Double( 2828e4 ) },
    { "D", "GARBAGE"} };

Map numberMap = ArrayUtils.toMap( mapArray );

double a = MapUtils.getDoubleValue( numberMap, "A" );
double b = MapUtils.getDoubleValue( numberMap, "B" );
double c = MapUtils.getDoubleValue( numberMap, "C" );
double d = MapUtils.getDoubleValue( numberMap, "D", new Double( Double.NaN ) );

System.out.println( "A = " + a );
System.out.println( "B = " + b );
System.out.println( "C = " + c );
System.out.println( "D = " + d );

This simple utility retrieves four doubles from numberMap; the fourth call to getDoubleValue( ) supplies a default double to be returned if the value’s type cannot be converted to a double. This example produces the following output:

A = 2.0
B = 0.223242
C = 28280.0
D = NaN

Discussion

This utility is laughably simple, but if you are working with numbers, this utility can help you avoid casting and calling doubleValue( ). In addition to MapUtils.getDoubleValue( ), MapUtils also contains the MapUtils.getDouble( ) ...