Check if a Class Object is subclass of another Class Object in Java
You want this method:
boolean isList = List.class.isAssignableFrom(myClass);
where in general, List
(above) should be replaced with superclass
and myClass
should be replaced with subclass
From the JavaDoc:
Determines if the class or interface represented by this
Class
object is either the same as, or is a superclass or superinterface of, the class or interface represented by the specifiedClass
parameter. It returnstrue
if so; otherwise it returnsfalse
. If thisClass
object represents a primitive type, this method returnstrue
if the specifiedClass
parameter is exactly thisClass
object; otherwise it returnsfalse
.
Reference:
Related:
a) Check if an Object is an instance of a Class or Interface (including subclasses) you know at compile time:
boolean isInstance = someObject instanceof SomeTypeOrInterface;
Example:
assertTrue(Arrays.asList("a", "b", "c") instanceof List<?>);
b) Check if an Object is an instance of a Class or Interface (including subclasses) you only know at runtime:
Class<?> typeOrInterface = // acquire class somehowboolean isInstance = typeOrInterface.isInstance(someObject);
Example:
public boolean checkForType(Object candidate, Class<?> type){ return type.isInstance(candidate);}
Another option is instanceof:
Object o =...if (o instanceof Number) { double d = ((Number)o).doubleValue(); //this cast is safe}
instanceof works on instances, i.e. on Objects. Sometimes you want to work directly with classes. In this case you can use the asSubClass method of the Class class.Some examples:
1)
Class o=Object.class; Class c=Class.forName("javax.swing.JFrame").asSubclass(o);
this will go through smoothly because JFrame is subclass of Object. c will contain a Class object representing the JFrame class.
2)
Class o=JButton.class; Class c=Class.forName("javax.swing.JFrame").asSubclass(o);
this will launch a java.lang.ClassCastException because JFrame is NOT subclass of JButton. c will not be initialized.
3)
Class o=Serializable.class; Class c=Class.forName("javax.swing.JFrame").asSubclass(o);
this will go through smoothly because JFrame implements the java.io.Serializable interface. c will contain a Class object representing the JFrame class.
Of course the needed imports have to be included.