Moved to core-java-function module

Added concurrent tests

core-java-modules/core-java-function/src/main/java/com/baeldung/lazylambda/LambdaSupplier.java

@@ -0,0 +1,16 @@
+package com.baeldung.lazylambda;
+
+import java.util.function.Supplier;
+
+public class LambdaSupplier<T> {
+
+    protected final Supplier<T> expensiveData;
+
+    public LambdaSupplier(Supplier<T> expensiveData) {
+        this.expensiveData = expensiveData;
+    }
+
+    public T getData() {
+        return expensiveData.get();
+    }
+}

core-java-modules/core-java-function/src/main/java/com/baeldung/lazylambda/LazyLambdaSupplier.java

@@ -0,0 +1,21 @@
+package com.baeldung.lazylambda;
+
+import java.util.function.Supplier;
+
+public class LazyLambdaSupplier<T> extends LambdaSupplier<T> {
+
+    private T data;
+
+    public LazyLambdaSupplier(Supplier<T> expensiveData) {
+        super(expensiveData);
+    }
+
+    @Override
+    public T getData() {
+        if (data != null) {
+            return data;
+        }
+        return data = expensiveData.get();
+    }
+
+}

core-java-modules/core-java-function/src/main/java/com/baeldung/lazylambda/LazyLambdaThreadSafeSupplier.java

@@ -0,0 +1,26 @@
+package com.baeldung.lazylambda;
+
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Supplier;
+
+public class LazyLambdaThreadSafeSupplier<T> extends LambdaSupplier<T> {
+
+    private final AtomicReference<T> data;
+
+    public LazyLambdaThreadSafeSupplier(Supplier<T> expensiveData) {
+        super(expensiveData);
+        data = new AtomicReference<>();
+    }
+
+    public T getData() {
+        if (data.get() == null) {
+            synchronized (data) {
+                if (data.get() == null) {
+                    data.set(expensiveData.get());
+                }
+            }
+        }
+        return data.get();
+    }
+
+}