RadioGroups contain Radio objects. The model for the RadioGroup is the object property, while the child Radio objects represent the set of values the property can be set to. Let's look at a trivial example, starting with a POJO:
public class MyObject
Next, the relevant snippet from the Form class:
MyObject bean=new MyObject();
RadioGroup myInt = new RadioGroup("group", new PropertyModel(bean, "myInt"));
myInt.add(new Radio("1", new Model(1)));
myInt.add(new Radio("2", new Model(2)));
myInt.add(new Radio("3", new Model(3)));
myInt.add(new Radio("4", new Model(4)));
add(myInt);
And finally, the markup:
<span wicket:id="group">
<input wicket:id="1" type="radio"/>
<input wicket:id="2" type="radio"/>
<input wicket:id="3" type="radio"/>
<input wicket:id="4" type="radio"/>
</span>
And that's all there is to using a RadioGroup with Radio instances.
Also note that the Radio components do not need to be direct children of the radio group, they can be anywhere in the component hierarchy below the RadioGroup component.