Advanced Collections and Collectors - Java 8 Lambdas - page 71

Figure 5-2. The groupingBy collector

NOTE

You might be familiar with group by from using SQL; here we have a method with a
similar concept, but implemented in the idioms of the streams library.

Strings

A very common reason for collecting streams of data is to generate strings at the end. Let's
suppose that we want to put together a formatted list of names of the artists involved in an al-
bum. So, for example, if our input album is Let It Be , then we're expecting our output to look
like "[George Harrison, John Lennon, Paul McCartney, Ringo Starr, The
Beatles]" .

If we were to implement this before Java 8, we might have come up with something like
Example 5-11 . Here, we use a StringBuilder to accumulate the values, iterating over the
list. At each step, we pull out the names of the artists and add them to the StringBuilder .

Example 5-11. Formatting artist names using a for loop
StringBuilder builder = new

new StringBuilder ( "[" );

for for ( Artist artist : artists ) {

iif ( builder . length () > 1 )
builder . append ( ", " );

String name = artist . getName ();
builder . append ( name );

}