Section 8.5 Anonymous Objects
It is not always necessary to assign an object to a variable before using the object again. This occurs in several situations, including when chaining methods. Consider the following code snippet.
String saying1 = "Be the change. "; // Create String object
String saying2 = saying1.trim(); // Trim whitespace
String saying3 = saying2.toUpperCase(); // Convert to upper case
System.out.println( saying3 ); // Print result
We know that String objects are immutable. Consequently, each time an operation is performed on a String, a new String object is created and returned. The String object count for the above example is 3. Three String objects are created in total.
We could simplify this just a bit by reusing the
saying String variable, as we did in the updated code snippet below. But it is important to realize that reusing the String variable does not change the fact that three String objects are created in the process. Our String object count remains 3.String saying = "Be the change. "; // Create String object
saying = saying.trim(); // Trim whitespace
saying = saying.toUpperCase(); // Convert to upper case
System.out.println( saying ); // Print result
Because each statement returns a new String object, there is no reason to assign results to the
saying String variable at all, other than for clarity. If our ultimate goal is to produce the printed output then why use the saying String variable? In fact, we could chain these statement into one complex statement and pass it as a parameter directly to the println(…) method. The JShell session that follows demonstrates this fact.// Create String object, process, and print
System.out.println( "Be the change. ".trim().toUpperCase() );
jshell> System.out.println( "Be the change. ".trim().toUpperCase() ); BE THE CHANGE. jshell>
What is our String count in the above single line print statement? Of course, the answer remains 3. Even though we did not use intermediate variables, the process remains the same. A String object was created, trimmed, which creates a second String, converted to upper-case, which creates a third, which is printed.
In situations like the above, when Java creates objects but does not assign them to a reference variable, we refer to the intermediate objects created as anonymous because they are never given a variable name. This does not mean that the objects were not created. In fact, they were, but they had a fleeting existence as they were returned from one method and used to invoke the next in a chain.
