Check if a Class Object is subclass of another Class Object in Java

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.

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 specified Class parameter. It returns true if so; otherwise it returns false. If this Class object represents a primitive type, this method returns true if the specified Class parameter is exactly this Class object; otherwise it returns false.

Reference:

• Class.isAssignableFrom(Class)

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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 somehow
boolean 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
}