Collections and Generics - SCJP Sun Certified Programmer for Java Platform SE6 - page 454

On line 6, if the data type of the argument passed in is Frame , the Frame is given a
size and displays. Within main , line 14 passes in a String object, so the T is a String
during that invocation. On line 15, an array of String objects is passed in, so T is of type
String [] for that invocation. Line 16 passes in a new Frame object, so line 6 is true and
a 100 100-pixel window displays after line 9 executes. The ship method also prints the

toString method of each argument, so the output to the command prompt is

Shipping a String object
Shipping [Ljava.lang.String;@3e25a5
Shipping java.awt.Frame[frame0,0,0,0x0,invalid,hidden,
layout=java.awt.BorderLayout,title=,resizable,normal]

The Syntax for Invoking a Generic Method

Generics have an optional syntax for specifying the type for a generic method. You can
place the data type of the generic in angle brackets, <> , after the dot operator and before
the method call. For example, the following statements are valid method invocations
of the ship method in the Box class:

Box.<String>ship(“a String object”);
Box.<String []>ship(args);
Box.<Frame>ship(new Frame());

The syntax makes the code more readable and also gives you control over the generic
type in situations where the type might not be obvious.

Let's look at another example of a generic method. Suppose we add the following
method to the Box class, which uses the generic Dish class discussed earlier in this section:

public static <U> void wrap(List<Dish<U>> list) {
for(Dish<U> dish : list) {
System.out.println(“Wrapping “ + dish);
}
}

The wrap method takes in a List of Dish objects with any data type for the Dish 's
generic. The for-each loop prints out each Dish<U> in the list. The following statements
demonstrate invoking the wrap method:

Dish<String> d1 = new Dish<String>();
Dish<String> d2 = new Dish<String>();
Dish<String> d3 = new Dish<String>();
List<Dish<String>> dishes = new ArrayList<Dish<String>>();