Not able to filter elements using an enum - java-8

Question

protected static double averagePrice( List<ComputerComponent> list ) {
return list.stream()
// .filter( line-> EnumUtils.isValidEnum(ComputerComponentCategory.class, line.getCategory()) )
// .filter( line-> isInEnum( line.getCategory(), ComputerComponentCategory.class) )
// .filter( line-> inEnum(line.getCategory(),EnumUtils.getEnumMap(ComputerComponentCategory.class ).keySet() ))
.filter( line ->
line.getCategory().contains("CPU")
|| line.getCategory().contains("GPU")
|| line.getCategory().contains("Monitor")
|| line.getCategory().contains("Keyboard")
|| line.getCategory().contains("Mouse")
|| line.getCategory().contains("Storage")
|| line.getCategory().contains("Memory"))
.mapToDouble(ComputerComponent::getPrice)
.average()
.orElseThrow(NoSuchElementException:: new);
}
I have an enum as
public enum ComputerComponentCategory {
CPU("CPU"),
MONITOR("Monitor"),
KEYBOARD("Keyboard"),
MOUSE("Mouse"),
GPU("GPU"),
MEMORY("Memory"),
STORAGE("Storage"),
NULL("NOT DEFINED");
private String label;
ComputerComponentCategory(String label) {
this.label = label;
}
public String getLabel() {
return this.label;
}
public static ComputerComponentCategory getValue(String label) {
switch(label) {
case "CPU":
return CPU;
case "Monitor":
return MONITOR;
case "Keyboard":
return KEYBOARD;
case "Mouse":
return MOUSE;
case "GPU":
return GPU;
case "Memory":
return MEMORY;
case "Storage":
return STORAGE;
default:
return NULL ;
}
}
}
I pass a list of ComputerComponent class to the averagePrice() function which has two fields of price
which is of type double and
category which is of type String.
My list has 4 elements with categories as "CPU", "Mouse",
"Keyboard" and "Storage" with their respective prices as 34.0, 155.0, 23.0 and 75.0.
When I try to use inEnum(), isInEnum() or EnumUtils.isValidEnum() functions, I get the average price
as 34.0 which I think that they just return the price of the first element rather than the average.
But when I do filtering using
.filter( line ->
line.getCategory().contains("CPU")
|| line.getCategory().contains("GPU")
|| line.getCategory().contains("Monitor")
|| line.getCategory().contains("Keyboard")
|| line.getCategory().contains("Mouse")
|| line.getCategory().contains("Storage")
|| line.getCategory().contains("Memory"))
I get the correct average value of 71.75.
The implementations that I have used for isInEnum() and inEnum() functions are the following:
public static <E extends Enum<E>> boolean isInEnum(String value, Class<E> enumClass) {
for (E e : enumClass.getEnumConstants()) {
if(e.name().contains(value)) { return true; }
}
return false;
}
public static boolean inEnum ( String category, Set<String> value ) {
for(String s: value ) {
if ( category.contains(s) ) {
return true ;
}
}
return false ;
}
How can I use enums correctly with java streams to filter by valid category names and get the correct
average value of price?
What mistake I am making when using streams and its functions ?

Answer 1

You could simply use your ComputerCategoryValue.getValue method and check for null, given the category of line:
public class EnumTest {
#Test
public void testBothMethods() {
final ComputerComponent c1 = new ComputerComponent(ComputerComponentCategory.CPU.getLabel(), 12.21);
final ComputerComponent c2 = new ComputerComponent(ComputerComponentCategory.MEMORY.getLabel(), 23.45);
final List<ComputerComponent> list = Arrays.asList(c1, c2);
assertEquals(averagePriceWithFilter(list), averagePriceWithInEnum(list), 0.01);
}
protected static double averagePriceWithFilter(final List<ComputerComponent> list) {
return list.stream()
.filter(line -> line.getCategory().contains("CPU")
|| line.getCategory().contains("GPU")
|| line.getCategory().contains("Monitor")
|| line.getCategory().contains("Keyboard")
|| line.getCategory().contains("Mouse")
|| line.getCategory().contains("Storage")
|| line.getCategory().contains("Memory"))
.mapToDouble(ComputerComponent::getPrice)
.average()
.orElseThrow(NoSuchElementException::new);
}
protected static double averagePriceWithInEnum(final List<ComputerComponent> list) {
return list.stream()
.filter(line -> ComputerComponentCategory.getValue(line.getCategory()) != null)
.mapToDouble(ComputerComponent::getPrice)
.average()
.orElseThrow(NoSuchElementException::new);
}
}
EDIT: explaining your mistakes:
EnumUtils.getEnumMap(ComputerComponentCategory.class).keySet()) returns a map of the enum name (not its label), so that the check will only work for CPU as there name and label are the same.
Same for the other method!
You need to use getLabel() instead of name() or use equalsIgnoreCase instead of contains.