This example will show you four different ways to implement this functional interface in your code — starting with how to use an actual class, and how to create very concise code with a lambda ...

as in the following example. String s1 = new String("Hello world!"); That code will create an s1 string object and a reference variable. As noted, Java strings are immutable. Once created, a string ...

It’s a good idea to use an abstract class when you need to implement mutable state. As an example, the Java Collections Framework includes the AbstractList class, which uses the state of variables.