Json Gson 是否必须使用默认的无参数构造函数

Gson user guide states that we should define default no-args constructor for any class to work with Gson properly. Even more, in the javadoc on Gson's InstanceCreator class said that exception will be thrown if we try to deserialize instance of class missing default constructor and we should use InstanceCreator in such cases. However, I've tried to test use Gson with class lacking default constructor and both serialization and deserialization work without any trouble.

Here is the piece of code for deserializaiton. A class without non-args constructor:

public class Mushroom {
    private String name;
    private double diameter;

    public Mushroom(String name, double diameter) {
        this.name = name;
        this.diameter = diameter;
    }

    //equals(), hashCode(), etc.
}

and a test:

@Test
public void deserializeMushroom() {
    assertEquals(
            new Mushroom("Fly agaric", 4.0),
            new Gson().fromJson(
                    "{name:\"Fly agaric\", diameter:4.0}", Mushroom.class));
}

这很好用.

所以我的问题是:could I actually use Gson without need to have default constructor or there is any circumstances when it will not work?