Java 8: Lambda Expression, Functional Interface and Stream

LambdaExpression.java

public class ProductUtil {

  private static final Comparator<Product> sortByRatingAscStrategy = (product1, product2) -> {
      if (product1 == null || product2 == null)
          return -1;
      return Double.compare(product1.getRating(), product2.getRating());
  };
  
  public static void main(String [] args){
      List<Product> productList = new ArrayList<>(2);
      productList.add(new Product("Model-1", 4, 129));
      productList.add(new Product("Model-2", 4.5, 139));
      
      /*
        Following sort invocations produce the same result
        They only differ in the way lambda expression is being used
      */
      
      //Lambda expression used directly
      Collections.sort(productList, (product1, product2) -> {
          if (product1 == null || product2 == null)
              return -1;
          return Double.compare(product1.getRating(), product2.getRating());
      });
      
      //Lambda expression defined as a class variable for reuse
      Collections.sort(productList, sortByRatingAscStrategy);
      
  }
  
}