I have List object and I need to take the first element on the list if it is not null or empty.
I write below code using java and now I want to convert it to Java 8.
List<DD> container
A<DD,DI> a;
if(container!=null || !container.isEmpty()){
for(DD dd:container)
{
a = dd.getPrescription();
break;
}
}
I convert it like this.
DD detail = container.stream().findFirst().get();
I need to know this is correct?
There is a critical flaw in your current code, i.e.
if(container!=null || !container.isEmpty())
this can still throw a NullPointerException (when container == null), unless the conditional operator is changed to &&. Post which the implementation below would be what I would suggest following.
It's almost correct, in the sense that you need to handle some default value if the conditions are not met :
DD detail = container.stream().findFirst().orElse(null); // or some default value instead of 'null'
If the container itself could be null, use
DD detail = container != null ?
container.stream().findFirst().orElse(null) : null;
In the case when you need the prescription from this object, use map as :
container.stream().findFirst().map(DD::getPrescription).orElse(null)
// ^^
// return type of prescription then
With Java-9, this could have been much simpler as :
A<DD, DI> basePrescription = Stream.ofNullable(container) // Java-9 API
.flatMap(List::stream)
.findFirst()
.map(DD::getPrescription)
.orElse(null);
container can be null as per OP's original code. You might want to change this to detail = container != null ? container.stream().findFirst().orElse(<someDefaultValue>) : <someDefaultValue>; or do a regular null check
null. Edited to include a cleaner java-9 solution as well though.container.stream()... no elements hence findFirst returns Optional.empty and hence orElse(null) comes into picture.. in short it would return null.This is way easier:
A<DD,DI> a = container.get(0).getPrescription();
While this is a direct translation of your original code, you probably intended something like that:
A<DD,DI> a = container != null && !container.isEmpty()
? container.get(0).getPrescription()
: null;
container.isEmpty() will throw. But I assumed OP knows how to do null checks.As of JDK9, there is a new method T requireNonNullElse(T obj, T defaultObj) which essentially returns the first argument if it is non-null and otherwise returns the non-null second argument.
We can, therefore, simplify your code to:
Objects.requireNonNullElse(container, Collections.emptyList())
.stream()
.findFirst()
.map(DD::getPrescription);
This returns an Optional<T> where T is whatever type getPrescription is. depending on the context and whether it's appropriate you might want to use .orElse(null); to get the value the optional contains or else a null value but there are also several other methods in the Optional<T> API which you might find more useful when extracting the value from the optional.
The findFirst() method finds the first element in a Stream. This method is used when you specifically want the first element from a sequence.
a) container.stream().findFirst().orElse(null);
b) container.stream().filter(Objects::nonNull).findFirst().orElse(null);
c)container.stream().filter(StringUtils::isNotBlank).findFirst();
or as lambdas:
d)container.stream().filter(s -> StringUtils.isNotBlank(s)).findFirst();
e)container.stream().filter(StringUtils::isNotBlank).findFirst()
For reference:- http://www.geekabyte.io/2015/01/using-optional-effectively-in-java-8.html
