Resolve "Java memoizer"

Closes #120 (closed)

java-memoizers/src/main/java/fr/craft/memoizer/Memoizers.java

+package fr.craft.memoizer;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+public final class Memoizers {
+
+  private Memoizers() {
+  }
+
+  public static <Result> Supplier<Result> of(
+      Supplier<Result> supplier) {
+    return () -> of(dummy -> supplier.get()).apply(null);
+  }
+
+  public static <Input, Result> Function<Input, Result> of(
+      Function<Input, Result> function) {
+    return new MemoizedFunction<>(function);
+  }
+
+  private static class MemoizedFunction<Input, Result>
+      implements Function<Input, Result> {
+
+    private final Function<Input, Result> function;
+    private final Map<MemoizedInput<Input>, MemoizedResult<Result>> results = new ConcurrentHashMap<>();
+
+    public MemoizedFunction(
+        Function<Input, Result> function) {
+      this.function = function;
+    }
+
+    @Override
+    public Result apply(Input input) {
+      return results
+          .computeIfAbsent(new MemoizedInput<>(input),
+              this::toMemoizedResult)
+          .result();
+    }
+
+    private MemoizedResult<Result> toMemoizedResult(
+        MemoizedInput<Input> input) {
+      return new MemoizedResult<>(
+          function.apply(input.input()));
+    }
+
+    private static record MemoizedInput<Input> (
+        Input input) {
+    }
+
+    private static record MemoizedResult<Result> (
+        Result result) {
+    }
+  }
+}