Question

So I’ve run into something odd and I don’t know what it’s called so I’m having trouble finding out information about it, hence my question here.

I’ve run into an issue where if you create an array of any type and call getClass on this array in Java you will get an odd return. I am wondering why you get this specific return and what it means.

Code example is as follows:

byte[] me = new byte[1];
int[] me2 = new int[1];
double[] me3 = new double[1];
float[] me4 = new float[1];
String[] me5 = new String[1];
Integer[] me6 = new Integer[1];

System.out.println(me.getClass());                  
System.out.println(me2.getClass());                 
System.out.println(me3.getClass());                 
System.out.println(me4.getClass());                 
System.out.println(me5.getClass());
System.out.println(me6.getClass());

and the output is:

 class [B
 class [I
 class [D
 class [F
 class [Ljava.lang.String;
 class [Ljava.lang.Integer;

Answer 1

The toString method of Class invokes the getName method of Class which

Returns the name of the entity (class, interface, array class,
primitive type, or void) represented by this Class object, as a
String. If this class object represents a reference type that is not
an array type then the binary name of the class is returned, as
specified by The Java™ Language Specification.

If this class object represents a primitive type or void, then the
name returned is a String equal to the Java language keyword
corresponding to the primitive type or void.

If this class object represents a class of arrays, then the internal
form of the name consists of the name of the element type preceded by
one or more ‘[‘ characters representing the depth of the array
nesting. The encoding of element type names is as follows:

 Element Type           Encoding
 boolean                Z
 byte                   B
 char                   C
 class or interface     Lclassname;
 double                 D
 float                  F
 int                    I
 long                   J
 short                  S 

The class or interface name classname is the binary name of the class
specified above.

Examples:

 String.class.getName()
     returns "java.lang.String"
 byte.class.getName()
     returns "byte"
 (new Object[3]).getClass().getName()
     returns "[Ljava.lang.Object;"
 (new int[3][4][5][6][7][8][9]).getClass().getName()
     returns "[[[[[[[I"