[JAVA] Ideal and reality that I felt when I used Optional for the first time ~ Implementation of cache using Map ~


Keep the value in Map If there is already a value in Map, it is the story when I implemented it to use that.

that time, Map # put () does not return the put value as it is, I couldn't write it as I expected, that is, it's a complaint: cry: (Specifically, refer to the source code: pencil :)

※perhaps, There may be a smart solution and Maybe it's just a misunderstanding: thinking:

Source code


import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        //Ideal (I want to write like this)
        String idealKey = "idealKey";
        Map<String, String> idealMap = new HashMap<String, String>();
        String idealValue = Optional.ofNullable(
            //put returns null ...
            () -> idealMap.put(idealKey, "idealValue")
        System.out.println("get:" + idealValue);

        //Reality (I ended up writing this)
        String realKey = "realKey";
        Map<String, String> realMap = new HashMap<String, String>();
        String realStr = Optional.ofNullable(
        ).orElseGet(() -> {
            String value = "realValue";
	        realMap.put(realKey, value);
        	return value;
        System.out.println("get:" + realStr);

Execution result


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