BAEL-2312 - Abstract Classes in Java (#5598)

* Initial Commit

* Add files via upload

* Update UppercaseFileReaderUnitTest.java

core-java/src/test/java/com/baeldung/abstractclasses/LowercaseFileReaderUnitTest.java

@@ -0,0 +1,18 @@
+package com.baeldung.abstractclasses;
+
+import com.baeldung.abstractclasses.filereaders.BaseFileReader;
+import com.baeldung.abstractclasses.filereaders.LowercaseFileReader;
+import java.util.List;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class LowercaseFileReaderUnitTest {
+    
+    @Test
+    public void givenLowercaseFileReaderInstance_whenCalledreadFile_thenCorrect() throws Exception {
+        String filePath = getClass().getClassLoader().getResource("files/test.txt").getPath().substring(1);
+        BaseFileReader lowercaseFileReader = new LowercaseFileReader(filePath);
+        
+        assertThat(lowercaseFileReader.readFile()).isInstanceOf(List.class);
+    }
+}

core-java/src/test/java/com/baeldung/abstractclasses/StandardFileReaderUnitTest.java

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+package com.baeldung.abstractclasses;
+
+import com.baeldung.abstractclasses.filereaders.BaseFileReader;
+import com.baeldung.abstractclasses.filereaders.StandardFileReader;
+import java.util.List;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class StandardFileReaderUnitTest {
+
+    @Test
+    public void givenStandardFileReaderInstance_whenCalledreadFile_thenCorrect() throws Exception {
+        String filePath = getClass().getClassLoader().getResource("files/test.txt").getPath().substring(1);
+        BaseFileReader standardFileReader = new StandardFileReader(filePath);
+        
+        assertThat(standardFileReader.readFile()).isInstanceOf(List.class);
+    }
+}

core-java/src/test/java/com/baeldung/abstractclasses/UppercaseFileReaderUnitTest.java

@@ -0,0 +1,18 @@
+package com.baeldung.abstractclasses;
+
+import com.baeldung.abstractclasses.filereaders.BaseFileReader;
+import com.baeldung.abstractclasses.filereaders.UppercaseFileReader;
+import java.util.List;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class UppercaseFileReaderUnitTest {
+
+    @Test
+    public void givenUppercaseFileReaderInstance_whenCalledreadFile_thenCorrect() throws Exception {
+        String filePath = getClass().getClassLoader().getResource("files/test.txt").getPath().substring(1);
+        BaseFileReader uppercaseFileReader = new UppercaseFileReader(filePath);
+        
+        assertThat(uppercaseFileReader.readFile()).isInstanceOf(List.class);
+    }
+}