Created with Copy to Gist

gist.java

interface Json{
    default <T> T as(){
        return (T) this;
    }
    default <T> T as(Class<T> clazz){
        return clazz.cast(this);
    }
}

class JsObject implements Json{
    private Map<String, Json> value;

    JsObject(Map<String, Json> map) {
        this.value = map;
    }

    public Map<String, Json> get() {
        return value;
    }
}

class JsString implements Json{
    private String value;

    JsString(String value) {
        this.value = value;
    }

    public String get() {
        return value;
    }
}

class JsNumber implements Json{
    private double value;

    JsNumber(double value) {
        this.value = value;
    }

    public double get() {
        return value;
    }
}

final class JsNull implements Json{
    private static final JsNull instance = new JsNull();
    private JsNull(){
    }

    public static JsNull get(){
        return instance;
    }
}