Constructor Selection Policy

When AutoParams generates instances of complex types that have multiple constructors, it follows a specific policy to determine which constructor to use:

1. Constructors annotated with @ConstructorProperties are prioritized.
2. If no such annotation is present, AutoParams chooses the constructor with the fewest parameters.

Here's an example:

Java

@Getter
public class ComplexObject {

    private final int value1;
    private final String value2;
    private final UUID value3;

    @ConstructorProperties({ "value1", "value2", "value3" })
    public ComplexObject(int value1, String value2, UUID value3) {
        this.value1 = value1;
        this.value2 = value2;
        this.value3 = value3;
    }

    @ConstructorProperties({ "value1", "value2" })
    public ComplexObject(int value1, String value2) {
        this(value1, value2, null);
    }

    public ComplexObject(int value1) {
        this(value1, null, null);
    }
}

Kotlin

class ComplexObject @ConstructorProperties("value1", "value2", "value3") constructor(
    val value1: Int,
    val value2: String?,
    val value3: UUID?
) {
    @ConstructorProperties("value1", "value2")
    constructor(value1: Int, value2: String?) : this(value1, value2, null)

    constructor(value1: Int) : this(value1, null, null)
}

Java

@Test
@AutoParams
void testMethod(ComplexObject object) {
    assertNotNull(object.getValue2());
    assertNull(object.getValue3());
}

Kotlin

@Test
@AutoParams
fun testMethod(obj: ComplexObject) {
    assertNotNull(obj.value2)
    assertNull(obj.value3)
}

In this example, AutoParams selects the constructor with the @ConstructorProperties annotation that has the fewest parameters—(int, String)—and assigns null to the value3 field. This shows how constructor selection can affect the structure of the generated object.