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There is a newer version: 8.6.0.37351

A Single Abstract Method (SAM) interface is a Java interface containing only one method. The Java API is full of SAM interfaces, such as java.lang.Runnable, java.awt.event.ActionListener, java.util.Comparator and java.util.concurrent.Callable. SAM interfaces have a special place in Java 8 because they can be implemented using Lambda expressions or Method references. 
Using @FunctionalInterface forces a compile break when an additional, non-overriding abstract method is added to a SAM, which would break the use of Lambda implementations.


  Note that this rule is automatically disabled when the project's sonar.java.source is lower than 8.


Noncompliant Code Example

public interface Changeable<T> {
  public void change(T o);
}

Compliant Solution

@FunctionalInterface
public interface Changeable<T> {
  public void change(T o);
}