Item 42: Prefer lambdas to anonymous classes

42. You should choose a lambda expression from the anonymous class

• Lambda expressions should be used rather than anonymous classes because they are more concise and clear.

package tryAny.effectiveJava;

import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class AnonymouseVsLambda {
    public static void main(String[] args) {
        List<String> words1 = Arrays.asList("apple", "pen", "pineapple");
        //Write in an anonymous class.
        Collections.sort(words1, new Comparator<String>() {
            public int compare(String s1, String s2) {
                return Integer.compare(s1.length(), s2.length());
            }
        });
        System.out.println(words1);

        //If the type is Raw, a compile error will occur.
        List<String> words2 = Arrays.asList("banana", "grape", "melon");
        //Write in a lambda expression.
        Collections.sort(words2, (s1, s2) -> Integer.compare(s1.length(), s2.length()));
        System.out.println(words2);
    }
}

• Lambda expression types can be omitted unless the code is clean by writing.
• Unlike classes and methods, lambda expressions have no name or documentation, so processes that are not trivial or have more than 4 lines should not be described in lambda expressions.
• The following are the situations where an anonymous class is required.
• Lambda expressions can only be assigned to functional interface types, so use anonymous classes if you need an interface with multiple methods or an instance of an abstract class.
• In a lambda expression, this refers to the enclosing class (outer class), but in anonymous classes it refers to the anonymous class itself, so if you need access to the function object itself, use the anonymous class.