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  1. import java.util.*;
  2. import java.lang.*;
  3. import java.io.*;
  4. import java.util.function.*;
  5.  
  6. class Ideone
  7. {
  8.     public static void main (String[] args) throws java.lang.Exception
  9.     {
  10.         StringUtil.indexOf("hello, world", 'l')
  11.             .DoIfSuccess(foundIndex -> {
  12.                 System.out.println(String.format("index=%d", foundIndex));
  13.             });
  14.     }
  15. }
  16.  
  17. class StringUtil {
  18.     public static Maybe<Integer> indexOf(String haystack, char needle) {
  19.         for (int i = 0; i < haystack.length(); ++i)
  20.             if (haystack.charAt(i) == needle)
  21.                 return Maybe.<Integer>just(i);
  22.         return Maybe.<Integer>nothing();
  23.     }
  24. }
  25.  
  26. class Maybe<ResultType> {
  27.     public static <R> Maybe<R> nothing() {
  28.         return new Maybe(false, null);
  29.     }
  30.  
  31.     public static <R> Maybe<R> just(R resultValue) {
  32.         return new Maybe(true, resultValue);
  33.     }
  34.  
  35.     private final boolean isSucceeded;
  36.     private final ResultType resultValue;
  37.  
  38.     private Maybe(boolean isSucceeded, ResultType resultValue) {
  39.         this.isSucceeded = isSucceeded;
  40.         this.resultValue = resultValue;
  41.     }
  42.  
  43.     public void DoIfSuccess(Consumer<ResultType> postAction) {
  44.         if (isSucceeded && postAction != null)
  45.             postAction.accept(resultValue);
  46.     }
  47. }
Success #stdin #stdout 0.14s 2184192KB
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Standard input is empty
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index=2
https://ideone.com/GbP1Zg
qiita - maybe sample impl
language:
Java (HotSpot 12)
created:
5 years ago
visibility:
public

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