[JAVA] I was curious about how to use Optional orElse () and orElseGet () properly.


At the time of writing this article, I don't know much about the grammar of java.util.Optional.

Optional is what

Class added in Java8-java.util.Optional

** A container object that may or may not contain non-null values. ** ** by https://docs.oracle.com/javase/jp/8/docs/api/java/util/Optional.html

I see, I don't know.


Trial code for the time being


import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {

        Optional.of("hoge").orElseGet(() -> {
            System.out.println("It's not executed or ElseGet");
            return "";

        Optional.empty().orElseGet(() -> {
            System.out.println("It's orElseGet to be executed");
            return "";

        String piyo = (String)Optional.of("hoge").orElse("It's not returned or Else");
        System.out.println("piyo: " + piyo);

        String piyo2 = (String)Optional.empty().orElse("It's returned or Else");
        System.out.println("piyo2: " + piyo2);



It's orElseGet to be executed piyo: hoge piyo2: It's returned or Else

In other words ...?

orElse () is executed regardless of whether the contents of Optional are null, and oeElseGet () is executed only when null.


--OrElse () is good because it is useless to write a lambda expression just to return a constant like "returns an empty string or zero if null" --OrElseGet () in the case of "If it is null, do some processing and return the result"

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