Java: class names

In Java, it is possible to get a String representation of a class by calling the Class.getName() method. Since Java 1.5 (AKA Java 5), it has been possible to get the canonical name using Class.getCanonicalName().

javadoc: java.lang.Class

For many classes, these two methods will return identical values. Things get more interesting when it comes to some of the more esoteric types such as arrays and inner classes. The code is provided for completeness, but feel free to skip to the output table.

public class ClassFoo {   enum FooEnum {     VAL1,     VAL2,   }   interface InterfaceBar {}   class InnerClassFoo2 {}      public static Class<?> getAnonymousInnerClass() {     return new Object(){}.getClass();   }      public static Class<?> getLocalInnerClass() {     class X extends Object {}     return X.class;   }    }

Using the example class above, the following code introspects the types:

Class<?>[] someTypes = {         String.class,         String[].class,         String[][].class,         Integer.class,         Integer.TYPE,         int[].class,         int[][].class,         ClassFoo.class,         ClassFoo.FooEnum.VAL1.getClass(),         ClassFoo.InnerClassFoo2.class,         ClassFoo.InterfaceBar.class,         ClassFoo.getAnonymousInnerClass(),         ClassFoo.getLocalInnerClass(),         Void.TYPE,     };          for(int i=0; i<someTypes.length; i++) {       Class<?> c = someTypes[i];       System.out.print(c.getName());       System.out.print('\t');       System.out.println(c.getCanonicalName());     }

The following table lists the output.

Class Instance	Class.getName()	Class.getCanonicalName()	Notes
String.class	java.lang.String	java.lang.String
String[].class	[Ljava.lang.String;	java.lang.String[]	string array
String[][].class	[[Ljava.lang.String;	java.lang.String[][]	two-dimensional string array
Integer.class	java.lang.Integer	java.lang.Integer	Integer object
Integer.TYPE	int	int	primitive int
int[].class	[I	int[]	int array
int[][].class	[[I	int[][]	two-dimensional int array
ClassFoo.class	ClassFoo	ClassFoo	(default package)
ClassFoo.FooEnum.VAL1.getClass()	ClassFoo$FooEnum	ClassFoo.FooEnum	inner enumeration
ClassFoo.InnerClassFoo2.class	ClassFoo$InnerClassFoo2	ClassFoo.InnerClassFoo2	inner class
ClassFoo.InterfaceBar.class	ClassFoo$InterfaceBar	ClassFoo.InterfaceBar	inner interface
ClassFoo.getAnonymousInnerClass()	ClassFoo$1	null	anonymous inner class
ClassFoo.getLocalInnerClass()	ClassFoo$1X	null	local inner class
Void.TYPE	void	void	void type

Note that in the case of arrays, class names are prefixed by the number of '[' characters equivalent to the number of array dimensions followed by a letter constant. For example, [I is the class name for an int[] object and [L denotes any object array. The remaining primitive types are listed in the javadoc.

Which value to use depends on the application. getCanonicalName() is useful for displaying the type to developers or generating code. getName() provides more useful information on inner types and corresponds more closely to the class names as defined in class repositories (like JAR files). For example, the following is the valid method for loading the type InnerClassFoo2.

ClassLoader.getSystemClassLoader().loadClass("ClassFoo$InnerClassFoo2")