One issue with anonymous classes is that if the implementation of your anonymous class is very simple, such as an interface that contains only one method, then the syntax of anonymous classes may seem unwieldy and unclear. In these cases, you’re usually trying to pass functionality as an argument to another method, such as what action should be taken when someone clicks a button. Lambda expressions enable you to do this, to treat functionality as method argument, or code as data.

The previous section, Anonymous Classes, shows you how to implement a base class without giving it a name. Although this is often more concise than a named class, for classes with only one method, even an anonymous class seems a bit excessive and cumbersome. Lambda expressions let you express instances of single-method classes more compactly.

Ideal Use Case for Lambda Expressions

Suppose that you are creating a social networking application. You want to create a feature that enables an administrator to perform any kind of action, such as sending a message, on members of the social networking application that satisfy certain criteria. The following table describes this use case in detail:

Field Description
Name           Perform action on selected members
Primary Actor           Administrator
Preconditions          Administrator is logged in to the system.
Postconditions          Action is performed only on members that fit the specified criteria.
Main Success Scenario
  1. Administrator specifies criteria of members on which to perform a certain action.
  2. Administrator specifies an action to perform on those selected members.
  3. Administrator selects the Submit button.
  4. The system finds all members that match the specified criteria.
  5. The system performs the specified action on all matching members.
Extensions         1a. Administrator has an option to preview those members who match the specified criteria before he or she specifies the action to be performed or before selecting the Submit button.
Frequency of Occurrence         Many times during the day.