// If not initialized at class/member level, it will be set to null
Integer x = 0;
Integer y; // y is null here
Integer p,q,r; // declare multiple variables
Integer i=1,j=2,k=3; // declare and initialize

/*
 * Similar to Integer, below variables can be initialized together separated by ','.
*/
String s = 'a string';
Decimal d = 0.0;
Double dbl = 0.0;
Blob blb = Blob.valueOf('Any String');
Boolean b = true;
AClassName cls = new AClassName();