Constructor for Instant class in Java?

Question

I know that I can create an Instant object in this way:

Instant instant = Instant.now();

And I don't understand why I can't create an Instant object like this:

Instant instant1 = new Instant();

I can't find any informations about Instant constructors, and I know Instant is not an interface or abstract class. Why I can't create an Instant object?

Thanks in advance!

Because the designers decided not to expose any constructor, and to promote factory methods instead. `Instant.now()` is much clearer than `new Instant()`. `Instant.ofEpochMilli(34567L)` is much clearer than `new Instant(34567L)`. — JB Nizet, Jun 01 '18 at 10:47
read this [Java Pattern class doesn't have a public constructor, why?](https://stackoverflow.com/questions/13758740/java-pattern-class-doesnt-have-a-public-constructor-why) — Youcef LAIDANI, Jun 01 '18 at 10:54

Max Vollmer · Answer 1 · 2018-06-01T10:50:33.303

3

Because the constructor is private. Don't forget that there are open source implementations of Java, and you can simply look at their implementations for such questions:

/**
 * Constructs an instance of {@code Instant} using seconds from the epoch of
 * 1970-01-01T00:00:00Z and nanosecond fraction of second.
 *
 * @param epochSecond  the number of seconds from 1970-01-01T00:00:00Z
 * @param nanos  the nanoseconds within the second, must be positive
 */
private Instant(long epochSecond, int nanos) {
    super();
    this.seconds = epochSecond;
    this.nanos = nanos;
}

edited Jun 01 '18 at 10:50

answered Jun 01 '18 at 10:48

Max Vollmer

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@pkpnd The `java.time` implementation is open source; it wasn't built by Oracle, and most of Oracle's Java is identical to OpenJDK, which is open source. – Mark Rotteveel Jun 01 '18 at 10:52

k_ssb · Answer 2 · 2018-06-01T10:50:38.770

2

The Instant source code declares a private constructor taking 2 arguments, which prevents auto-generation of the no-arg constructor. This is by design: the authors of the Instant source code wanted to prevent users from using the constructor, because they wanted to force users to use Instant.now() instead.

edited Jun 01 '18 at 10:50

answered Jun 01 '18 at 10:48

k_ssb

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score 0 · Answer 3 · answered Sep 13 '21 at 17:10

Private constructor is used because:

Sometimes we want to use the Singleton Design pattern. To achieve this, we declare our class's constructor as private and we create the now() method to provide this functionality.
Singleton Design pattern provides only one object for the entire system so that we don't end up creating multiple objects which optimize our code and garbage collection.
Hope I answered

Constructor for Instant class in Java?

3 Answers3