I know that you can't use the delegated property syntax in Java, and won't get the convenience of "overriding" the set/get operators as in Kotlin, but I'd still like to use an existing property delegate in Java.
For instance, a simple delegate of an int:
class IntDelegate {
operator fun getValue(thisRef: Any?, property: KProperty<*>) = 0
}
In Kotlin of course we can use this like so:
val x by IntDelegate()
But how can we use IntDelegate in some form in Java? This is the start, I believe:
final IntDelegate x = new IntDelegate();
And then using the functions directly. But how can I use the getValue function? What do I pass for its parameters? How do I get a KProperty for Java field?
If you really want to know how Kotlin delegated property looks under the hood in Java, here it is: in this example a property x of a java class JavaClass is delegated to the Delegates.notNull standard delegate.
// delegation implementation details
import kotlin.jvm.JvmClassMappingKt;
import kotlin.jvm.internal.MutablePropertyReference1Impl;
import kotlin.jvm.internal.Reflection;
import kotlin.reflect.KProperty1;
// notNull property delegate from stdlib
import kotlin.properties.Delegates;
import kotlin.properties.ReadWriteProperty;
class JavaClass {
private final ReadWriteProperty<Object, String> x_delegate = Delegates.INSTANCE.notNull();
private final static KProperty1 x_property = Reflection.mutableProperty1(
new MutablePropertyReference1Impl(
JvmClassMappingKt.getKotlinClass(JavaClass.class), "x", "<no_signature>"));
public String getX() {
return x_delegate.getValue(this, x_property);
}
public void setX(String value) {
x_delegate.setValue(this, x_property, value);
}
}
class Usage {
public static void main(String[] args) {
JavaClass instance = new JavaClass();
instance.setX("new value");
System.out.println(instance.getX());
}
}
However I wouldn't recommend to use this solution, not only because of the boilerplate required, but because it relies heavily on the implementation details of the delegated properties and kotlin reflection.