在Java中调用Kotlin时，如何使用默认值省略构造函数参数？

Question

My kotlin file:

class Chat(var name: String, var age: Int? = 18)

My java file only can do this:

new Chat("John",18);

But could i just write this ?

new Chat("John");

Answer 1

From Kotlin document :

Normally, if you write a Kotlin method with default parameter values, it will be visible in Java only as a full signature, with all parameters present. If you wish to expose multiple overloads to Java callers, you can use the @JvmOverloads annotation.

So, if you want to initialize Chat with name only in Java, you have to add @JvmOverloads annotation to the constructor.

class Chat @JvmOverloads constructor(var name: String, var age: Int? = 18)

It will generate additional overload for each parameter with a default value.

public Chat(String name) {}
public Chat(String name, Integer age) {}