java - Is there a way to recognise a Java 16 record's canonical constructor via reflection?

Question

Assuming I have a record like this (or any other record):

record X(int i, int j) {
    X(int i) {
        this(i, 0);
    }
    X() {
        this(0, 0);
    }
    X(String i, String j) {
        this(Integer.parseInt(i), Integer.parseInt(j));
    }
}

Is there a way to find this record's canonical constructor via reflection, i.e. the one that is implicitly declared in the RecordHeader?

标签： javareflectionjava-recordjava-16

Answer 1

Try this

static <T extends Record> Constructor<T> canonicalConstructorOfRecord(Class<T> recordClass)
        throws NoSuchMethodException, SecurityException {
    Class<?>[] componentTypes = Arrays.stream(recordClass.getRecordComponents())
        .map(rc -> rc.getType())
        .toArray(Class<?>[]::new);
    return recordClass.getDeclaredConstructor(componentTypes);
}

And

Constructor<X> c = canonicalConstructorOfRecord(X.class);
X x = c.newInstance(1, 2);
System.out.println(x);

Output

X[i=1, j=2]