Moved to core-java-function module

Added concurrent tests

core-java-modules/core-java-21/src/test/java/com/baeldung/lazylambda/LazyLambdaSupplierUnitTest.java

@@ -1,26 +0,0 @@
-package com.baeldung.lazylambda;
-
-import java.util.function.Supplier;
-
-import org.junit.Test;
-import org.mockito.Mockito;
-
-public class LazyLambdaSupplierUnitTest {
-
-    @Test
-    public void whenCalledMultipleTimes_thenShouldBeCalledOnlyOnce() {
-        @SuppressWarnings("unchecked") Supplier<String> mockedExpensiveFunction = Mockito.mock(Supplier.class);
-        Mockito.when(mockedExpensiveFunction.get())
-            .thenReturn("expensive call");
-        LazyLambdaSupplier<String> testee = new LazyLambdaSupplier<>(mockedExpensiveFunction);
-        Mockito.verify(mockedExpensiveFunction, Mockito.never())
-            .get();
-        testee.getData();
-        testee.getData();
-        testee.getData();
-        testee.getData();
-        Mockito.verify(mockedExpensiveFunction, Mockito.times(1))
-            .get();
-    }
-
-}

core-java-modules/core-java-21/src/test/java/com/baeldung/lazylambda/LazyLambdaThreadSafeSupplierUnitTest.java

@@ -1,26 +0,0 @@
-package com.baeldung.lazylambda;
-
-import java.util.function.Supplier;
-
-import org.junit.Test;
-import org.mockito.Mockito;
-
-public class LazyLambdaThreadSafeSupplierUnitTest {
-
-    @Test
-    public void whenCalledMultipleTimes_thenShouldBeCalledOnlyOnce() {
-        @SuppressWarnings("unchecked") Supplier<String> mockedExpensiveFunction = Mockito.mock(Supplier.class);
-        Mockito.when(mockedExpensiveFunction.get())
-            .thenReturn("expensive call");
-        LazyLambdaThreadSafeSupplier<String> testee = new LazyLambdaThreadSafeSupplier<>(mockedExpensiveFunction);
-        Mockito.verify(mockedExpensiveFunction, Mockito.never())
-            .get();
-        testee.getData();
-        testee.getData();
-        testee.getData();
-        testee.getData();
-        Mockito.verify(mockedExpensiveFunction, Mockito.times(1))
-            .get();
-    }
-
-}

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

@@ -4,7 +4,7 @@ import java.util.function.Supplier;
 
 public class LambdaSupplier<T> {
 
-    private final Supplier<T> expensiveData;
+    protected final Supplier<T> expensiveData;
 
     public LambdaSupplier(Supplier<T> expensiveData) {
         this.expensiveData = expensiveData;

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

@@ -2,16 +2,15 @@ package com.baeldung.lazylambda;
 
 import java.util.function.Supplier;
 
-public class LazyLambdaSupplier<T> {
+public class LazyLambdaSupplier<T> extends LambdaSupplier<T> {
-
-    private final Supplier<T> expensiveData;
 
     private T data;
 
     public LazyLambdaSupplier(Supplier<T> expensiveData) {
-        this.expensiveData = expensiveData;
+        super(expensiveData);
     }
 
+    @Override
     public T getData() {
         if (data != null) {
             return data;

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

@@ -3,14 +3,12 @@ package com.baeldung.lazylambda;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Supplier;
 
-public class LazyLambdaThreadSafeSupplier<T> {
+public class LazyLambdaThreadSafeSupplier<T> extends LambdaSupplier<T> {
-
-    private final Supplier<T> expensiveData;
 
     private final AtomicReference<T> data;
 
     public LazyLambdaThreadSafeSupplier(Supplier<T> expensiveData) {
-        this.expensiveData = expensiveData;
+        super(expensiveData);
         data = new AtomicReference<>();
     }
 
@@ -22,7 +20,6 @@ public class LazyLambdaThreadSafeSupplier<T> {
                 }
             }
         }
-
         return data.get();
     }
 

core-java-modules/core-java-function/src/test/java/com/baeldung/lazylambda/LambdaSupplierUnitTest.java

@@ -17,9 +17,7 @@ public class LambdaSupplierUnitTest {
             .get();
         testee.getData();
         testee.getData();
-        testee.getData();
+        Mockito.verify(mockedExpensiveFunction, Mockito.times(2))
-        testee.getData();
-        Mockito.verify(mockedExpensiveFunction, Mockito.times(4))
             .get();
     }
 

core-java-modules/core-java-function/src/test/java/com/baeldung/lazylambda/LazyLambdaSupplierUnitTest.java

@@ -0,0 +1,51 @@
+package com.baeldung.lazylambda;
+
+import java.util.List;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.function.Supplier;
+
+import org.junit.Test;
+import org.mockito.Mockito;
+import org.mockito.stubbing.Answer;
+
+public class LazyLambdaSupplierUnitTest {
+
+    @Test
+    public void whenCalledMultipleTimes_thenShouldBeCalledOnlyOnce() {
+        @SuppressWarnings("unchecked") Supplier<String> mockedExpensiveFunction = Mockito.mock(Supplier.class);
+        Mockito.when(mockedExpensiveFunction.get())
+            .thenReturn("expensive call");
+        LazyLambdaSupplier<String> testee = new LazyLambdaSupplier<>(mockedExpensiveFunction);
+        Mockito.verify(mockedExpensiveFunction, Mockito.never())
+            .get();
+        testee.getData();
+        testee.getData();
+        Mockito.verify(mockedExpensiveFunction, Mockito.times(1))
+            .get();
+    }
+
+    @Test
+    public void whenCalledMultipleTimesConcurrently_thenShouldBeCalledMultipleTimes() throws InterruptedException {
+        @SuppressWarnings("unchecked") Supplier<String> mockedExpensiveFunction = Mockito.mock(Supplier.class);
+        Mockito.when(mockedExpensiveFunction.get())
+            .thenAnswer((Answer<String>) invocation -> {
+                Thread.sleep(1000L);
+                return "Late response!";
+            });
+        LazyLambdaSupplier<String> testee = new LazyLambdaSupplier<>(mockedExpensiveFunction);
+        Mockito.verify(mockedExpensiveFunction, Mockito.never())
+            .get();
+
+        ExecutorService executorService = Executors.newFixedThreadPool(4);
+        executorService.invokeAll(List.of(testee::getData, testee::getData));
+        executorService.shutdown();
+        if (!executorService.awaitTermination(5, TimeUnit.SECONDS)) {
+            executorService.shutdownNow();
+        }
+
+        Mockito.verify(mockedExpensiveFunction, Mockito.times(2))
+            .get();
+    }
+}

core-java-modules/core-java-function/src/test/java/com/baeldung/lazylambda/LazyLambdaThreadSafeSupplierUnitTest.java

@@ -0,0 +1,52 @@
+package com.baeldung.lazylambda;
+
+import java.util.List;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.function.Supplier;
+
+import org.junit.Test;
+import org.mockito.Mockito;
+import org.mockito.stubbing.Answer;
+
+public class LazyLambdaThreadSafeSupplierUnitTest {
+
+    @Test
+    public void whenCalledMultipleTimes_thenShouldBeCalledOnlyOnce() {
+        @SuppressWarnings("unchecked") Supplier<String> mockedExpensiveFunction = Mockito.mock(Supplier.class);
+        Mockito.when(mockedExpensiveFunction.get())
+            .thenReturn("expensive call");
+        LazyLambdaThreadSafeSupplier<String> testee = new LazyLambdaThreadSafeSupplier<>(mockedExpensiveFunction);
+        Mockito.verify(mockedExpensiveFunction, Mockito.never())
+            .get();
+        testee.getData();
+        testee.getData();
+        Mockito.verify(mockedExpensiveFunction, Mockito.times(1))
+            .get();
+    }
+
+    @Test
+    public void whenCalledMultipleTimesConcurrently_thenShouldBeCalledOnlyOnce() throws InterruptedException {
+        @SuppressWarnings("unchecked") Supplier<String> mockedExpensiveFunction = Mockito.mock(Supplier.class);
+        Mockito.when(mockedExpensiveFunction.get())
+            .thenAnswer((Answer<String>) invocation -> {
+                Thread.sleep(1000L);
+                return "Late response!";
+            });
+        LazyLambdaThreadSafeSupplier<String> testee = new LazyLambdaThreadSafeSupplier<>(mockedExpensiveFunction);
+        Mockito.verify(mockedExpensiveFunction, Mockito.never())
+            .get();
+
+        ExecutorService executorService = Executors.newFixedThreadPool(4);
+        executorService.invokeAll(List.of(testee::getData, testee::getData));
+        executorService.shutdown();
+        if (!executorService.awaitTermination(5, TimeUnit.SECONDS)) {
+            executorService.shutdownNow();
+        }
+
+        Mockito.verify(mockedExpensiveFunction, Mockito.times(1))
+            .get();
+    }
+
+}