Technotrance, Illusions and Perspectives

With introduction of Generics in Java, type checking in Java opened up a can of complex variations and concepts. During the compile type, the compiler enforces stricter type checking for a generics implements. That is

List<String> listOfStrings = new ArrayList<String>(1);
listOfStrings.add(new Integer(1)); //will throw a compilation error

However during the runtime, the JVM doesnt maintain type information about generics, and this is ‘type erasure’. So effectively a code snippet such as this

List<String> listOfStrings = new ArrayList<String>(1);
listOfStrings.add("HelloWorld");
String addedElement = listOfStrings.get(0);

would get converted to in

List listOfStrings = new ArrayList(1);
listOfStrings.add("HelloWorld");
String addedElement = (String)listOfStrings.get(0);

Behind the scenes, there are 2 passes of compilation, in which the first pass handles the type checking, and in the second pass, the type information is erased and written to the class file.