I have noted that many Java 8 methods in Oracle JDK use Objects.requireNonNull()
, which internally throws NullPointerException
if the given object (argument) is null
.
public static <T> T requireNonNull(T obj) { if (obj == null) throw new NullPointerException(); return obj; }
But NullPointerException
will be thrown anyway if a null
object is dereferenced. So, why should one do this extra null check and throw NullPointerException
?
One obvious answer (or benefit) is that it makes code more readable and I agree. I'm keen to know any other reasons for using Objects.requireNonNull()
in the beginning of the method.
requireNonNull. Checks that the specified object reference is not null and throws a customized NullPointerException if it is. Unlike the method requireNonNull(Object, String) , this method allows creation of the message to be deferred until after the null check is made.
The nonNull method is a static method of the Objects class in Java that checks whether the input object reference supplied to it is non-null or not. If the passed object is non-null, then the method returns true. If the passed object is null , then the method returns false.
Because you can make things explicit by doing so. Like:
public class Foo { private final Bar bar; public Foo(Bar bar) { Objects.requireNonNull(bar, "bar must not be null"); this.bar = bar; }
Or shorter:
this.bar = Objects.requireNonNull(bar, "bar must not be null");
Now you know:
new()
Compare that to: you create a Foo object today, and tomorrow you invoke a method that uses that field and throws. Most likely, you will not know tomorrow why that reference was null yesterday when it got passed to the constructor!
In other words: by explicitly using this method to check incoming references you can control the point in time when the exception will be thrown. And most of the time, you want to fail as fast as possible!
The major advantages are:
bar
isn't null - and thus you do not need any if (bar == null)
checks in other places!The code should crash as soon as possible. It should not do half of the work, dereference the null and only then crash, leaving half of some work done causing the system to be in an invalid state.
This is commonly called "fail early" or "fail-fast".
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