Lambda Expressions - Java 8 Lambdas - page 15

ory method for ThreadLocal that takes a lambda expression, letting you create a new
ThreadLocal without the syntactic burden of subclassing.

a. Find the method in Javadoc or using your IDE.

b. The Java DateFormatter class isn't thread-safe. Use the constructor to create
a thread-safe DateFormatter instance that prints dates like this:
“01-Jan-1970”.

3. Type inference rules . Here are a few examples of passing lambda expressions into
functions. Can javac infer correct argument types for the lambda expressions? In oth-
er words, will they compile?

a. Runnable helloWorld = () -> System.out.println("hello world");

b. The lambda expression being used as an ActionListener :

JButton button = new new JButton ();

button . addActionListener ( event ->
System . out . println ( event . getActionCommand ()));

c. Would check(x -> x > 5) be inferred, given the following overloads for
check ?

interface interface IntPred IntPred {

boolean boolean test ( Integer value );

}

boolean boolean check ( Predicate < Integer > predicate );

boolean boolean check ( IntPred predicate );

TIP

You might want to look up the method argument types in Javadoc or in your IDE in order
to determine whether there are multiple valid overloads.