Lazy chain

src/main/java/io/github/alexengrig/lambdax/LazyChainX.java

@@ -0,0 +1,84 @@
+/*
+ * Copyright 2019 - 2020 Alexengrig Dev.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.github.alexengrig.lambdax;
+
+import java.util.Optional;
+import java.util.function.Supplier;
+
+public class LazyChainX<T> {
+    protected static final LazyChainX<?> EMPTY = new LazyChainX<>();
+
+    protected final Supplier<? extends T> producer;
+
+    protected transient volatile T value;
+
+    protected LazyChainX() {
+        this.producer = () -> null;
+    }
+
+    protected LazyChainX(T value) {
+        this.producer = () -> value;
+    }
+
+    protected LazyChainX(Supplier<? extends T> producer) {
+        this.producer = producer;
+    }
+
+    @SuppressWarnings("unchecked")
+    public static <T> LazyChainX<T> empty() {
+        return (LazyChainX<T>) EMPTY;
+    }
+
+    public static <T> LazyChainX<T> of(T value) {
+        return new LazyChainX<>(value);
+    }
+
+    public static <T> LazyChainX<T> of(Supplier<? extends T> producer) {
+        return new LazyChainX<>(producer);
+    }
+
+    @SuppressWarnings("OptionalUsedAsFieldOrParameterType")
+    public static <T> LazyChainX<T> of(Optional<? extends T> optional) {
+        return new LazyChainX<>(() -> optional.orElse(null));
+    }
+
+//    Check
+
+    public final boolean isNull() {
+        return value() == null;
+    }
+
+    public final boolean nonNull() {
+        return value() != null;
+    }
+
+//    Value
+
+    public T value() {
+        T target = value;
+        if (target == null) {
+            synchronized (this) {
+                target = value;
+                if (target == null) {
+                    target = producer.get();
+                    value = target;
+                }
+            }
+        }
+        return target;
+    }
+}