Lambda expressions - Java 8 in Action: Lambdas, Streams, and Functional-Style Programming - page 50

5 . “Iron Man” is an expression, not a statement. To make this lambda valid, you can remove the
curly braces and semicolon as follows: (String s) -> "Iron Man". Or if you prefer, you can use an
explicit return statement as follows: (String s) -> {return "Iron Man";}.

Table 3.1 provides a list of example lambdas with examples of use cases.

Table 3.1. Examples of lambdas

Use case Examples of lambdas

A boolean expression (List<String> list) -> list.isEmpty()

Creating objects () -> new Apple(10)

Consuming from an object (Apple a) -> {

System.out.println(a.getWeight());

}

Select/extract from an object (String s) -> s.length()

Combine two values (int a, int b) -> a * b

Compare two objects (Apple a1, Apple a2) -> a1.getWeight().compareTo(a2.getWeight())

3.2. Where and how to use lambdas

You may now be wondering where you're allowed to use lambda expressions. In the previous
example, you assigned a lambda to a variable of type Comparator<Apple>. You could also use
another lambda with the filter method you implemented in the previous chapter:

List<Apple> greenApples =
filter(inventory, (Apple a) -> "green".equals(a.getColor()) );

So where exactly can you use lambdas? You can use a lambda expression in the context of a
functional interface. In the code shown here, you can pass a lambda as second argument to the
method filter because it expects a Predicate<T>, which is a functional interface. Don't worry if