Added enhancements and new tests in 'FileFilterTest.java' and a new f…

…ile 'LazySupplierTest.java'

Enhanced 'FileFilterTest.java' by adding code that includes new tests and methods for directory listing and '.java' files filtering using lambda expressions and method references. The reason for these enhancements is to validate the correct functionality of file fiters with lambda expressions and method references in addition to anonymous inner classes.

Further, a new test file 'LazySupplierTest.java' has been introduced in the lamdabas package to test Lazy supplier performance. This is to ensure that 'Supplier' actually provides lazy behaviour when using Lambda expressions, which are part of Java8 language improvements.

src/test/java/lambdas/FileFilterTest.java

@@ -4,6 +4,8 @@
 
 import java.io.File;
 import java.io.FileFilter;
+import java.io.FilenameFilter;
+import java.util.Map;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -41,6 +43,15 @@ void listDirectories_expressionLambda() {
         assertThat(directories.length).isEqualTo(14);
     }
 
+    @Test
+    void listDirectories_methodReference() {
+        FileFilter filter = File::isDirectory;
+        File[] directories = root.listFiles(filter);
+        assert directories != null;
+        assertEquals(14, directories.length);
+        assertThat(directories.length).isEqualTo(14);
+    }
+
     @Test
     void listDirectories_blockLambda() {
         FileFilter filter = pathname -> {
@@ -51,4 +62,31 @@ void listDirectories_blockLambda() {
         assertEquals(14, directories.length);
         assertThat(directories.length).isEqualTo(14);
     }
+
+    // Add a test that uses a FileFilter to list only .java files
+    @Test
+    void listJavaSrcFiles_fileFilter() {
+        FileFilter filter = pathname -> pathname.getName().endsWith(".java");
+        File[] javaFiles = root.listFiles(filter);
+        assert javaFiles != null;
+        assertThat(javaFiles.length).isEqualTo(8);
+    }
+
+    // Add a test that uses a FilenameFilter to list only .java files
+    @Test
+    void listJavaSrcFiles_filenameFilter() {
+        FilenameFilter filter = (dir, name) -> name.endsWith(".java");
+        File[] javaFiles = root.listFiles(filter);
+        assert javaFiles != null;
+        assertThat(javaFiles.length).isEqualTo(8);
+    }
+
+    @Test
+    void iterateOverMap() {
+        Map.ofEntries(
+                Map.entry("a", 1),
+                Map.entry("b", 2),
+                Map.entry("c", 3)
+        ).forEach((k, v) -> System.out.println(k + " = " + v));
+    }
 }

src/test/java/lambdas/LazySupplierTest.java

@@ -0,0 +1,35 @@
+package lambdas;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.logging.Logger;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class LazySupplierTest {
+    private final Logger logger = Logger.getLogger(LazySupplierTest.class.getName());
+
+    private String getErrorMessage() {
+        System.out.println("getErrorMessage() called");
+        return "Error message";
+    }
+
+    private String getLogMessage() {
+        System.out.println("getLogMessage() called");
+        return "Log message";
+    }
+
+    @Test
+    void eagerErrorMessage() {
+        boolean x = true;
+        logger.fine(getLogMessage());
+        assertTrue(x, getErrorMessage());
+    }
+
+    @Test
+    void lazyErrorMessage() {
+        boolean x = true;
+        logger.fine(() -> getLogMessage());
+        assertTrue(x, () -> getErrorMessage());
+    }
+}