BAEL-1261 Polymorphism in Java (#2762)

* Define beans for handling different message types in a lean chat app

* Add class based spring beans configuration

* Define spring configuration in XML for constructor based bean injection

* Refactor package structure to separate constructor based bean injection code set from setter based bean injection code set

* Define configuration and classes specific to setter-based bean injection.

* Implement tests for constructor-based and setter-based bean injections

* develop codes for explaining type erasure

* Write unit tests for type erasure examples

* Remove evaluation article code

* Modify type erasure examples and unit tests

* Modify type erasure examples and unit tests

* Add expected exception in TypeErasureUnitTest

* Correct grammar in class name

* Implement File Manager app to demonstrate Polymorphism. Develop unit tests for Polymorphism article code

* Add examples for static polymorphism

* Change sysout statments to slf4j log info statements

* Add assertions and expected errors check on Test

* Add assertions and expected errors check on Test

* Correct compile time error of symbol not found

* Removed commented out non-compiling test.

core-java/src/main/java/com/baeldung/polymorphism/FileManager.java

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+package com.baeldung.polymorphism;
+
+import java.awt.image.BufferedImage;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class FileManager {
+
+    final static Logger logger = LoggerFactory.getLogger(FileManager.class);
+
+    public static void main(String[] args) {
+        GenericFile file1 = new TextFile("SampleTextFile", "This is a sample text content", "v1.0.0");
+        logger.info("File Info: \n" + file1.getFileInfo() + "\n");
+        ImageFile imageFile = new ImageFile("SampleImageFile", 200, 100, new BufferedImage(100, 200, BufferedImage.TYPE_INT_RGB).toString()
+            .getBytes(), "v1.0.0");
+        logger.info("File Info: \n" + imageFile.getFileInfo());
+    }
+
+    public static ImageFile createImageFile(String name, int height, int width, byte[] content, String version) {
+        ImageFile imageFile = new ImageFile(name, height, width, content, version);
+        logger.info("File 2 Info: \n" + imageFile.getFileInfo());
+        return imageFile;
+    }
+
+    public static GenericFile createTextFile(String name, String content, String version) {
+        GenericFile file1 = new TextFile(name, content, version);
+        logger.info("File 1 Info: \n" + file1.getFileInfo() + "\n");
+        return file1;
+    }
+    
+    public static TextFile createTextFile2(String name, String content, String version) {
+        TextFile file1 = new TextFile(name, content, version);
+        logger.info("File 1 Info: \n" + file1.getFileInfo() + "\n");
+        return file1;
+    }
+
+}

core-java/src/main/java/com/baeldung/polymorphism/GenericFile.java

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+package com.baeldung.polymorphism;
+
+import java.util.Date;
+
+public class GenericFile {
+    private String name;
+    private String extension;
+    private Date dateCreated;
+    private String version;
+    private byte[] content;
+
+    public GenericFile() {
+        this.setDateCreated(new Date());
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getExtension() {
+        return extension;
+    }
+
+    public void setExtension(String extension) {
+        this.extension = extension;
+    }
+
+    public Date getDateCreated() {
+        return dateCreated;
+    }
+
+    public void setDateCreated(Date dateCreated) {
+        this.dateCreated = dateCreated;
+    }
+
+    public String getVersion() {
+        return version;
+    }
+
+    public void setVersion(String version) {
+        this.version = version;
+    }
+
+    public byte[] getContent() {
+        return content;
+    }
+
+    public void setContent(byte[] content) {
+        this.content = content;
+    }
+
+    public String getFileInfo() {
+        return "File Name: " + this.getName() + "\n" + "Extension: " + this.getExtension() + "\n" + "Date Created: " + this.getDateCreated() + "\n" + "Version: " + this.getVersion() + "\n";
+    }
+
+    public Object read() {
+        return content;
+    }
+}

core-java/src/main/java/com/baeldung/polymorphism/ImageFile.java

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+package com.baeldung.polymorphism;
+
+public class ImageFile extends GenericFile {
+    private int height;
+    private int width;
+
+    public ImageFile(String name, int height, int width, byte[] content, String version) {
+        this.setHeight(height);
+        this.setWidth(width);
+        this.setContent(content);
+        this.setName(name);
+        this.setVersion(version);
+        this.setExtension(".jpg");
+    }
+
+    public int getHeight() {
+        return height;
+    }
+
+    public void setHeight(int height) {
+        this.height = height;
+    }
+
+    public int getWidth() {
+        return width;
+    }
+
+    public void setWidth(int width) {
+        this.width = width;
+    }
+
+    public String getFileInfo() {
+        return super.getFileInfo() + "Height: " + this.getHeight() + "\n" + "Width: " + this.getWidth();
+    }
+
+    public String read() {
+        return this.getContent()
+            .toString();
+    }
+
+}

core-java/src/main/java/com/baeldung/polymorphism/TextFile.java

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+package com.baeldung.polymorphism;
+
+public class TextFile extends GenericFile {
+    private int wordCount;
+
+    public TextFile(String name, String content, String version) {
+        String[] words = content.split(" ");
+        this.setWordCount(words.length > 0 ? words.length : 1);
+        this.setContent(content.getBytes());
+        this.setName(name);
+        this.setVersion(version);
+        this.setExtension(".txt");
+    }
+
+    public int getWordCount() {
+        return wordCount;
+    }
+
+    public void setWordCount(int wordCount) {
+        this.wordCount = wordCount;
+    }
+
+    public String getFileInfo() {
+        return super.getFileInfo() + "Word Count: " + wordCount;
+    }
+
+    public String read() {
+        return this.getContent()
+            .toString();
+    }
+
+    public String read(int limit) {
+        return this.getContent()
+            .toString()
+            .substring(0, limit);
+    }
+
+    public String read(int start, int stop) {
+        return this.getContent()
+            .toString()
+            .substring(start, stop);
+    }
+
+}

core-java/src/test/java/com/baeldung/polymorphism/PolymorphismUnitTest.java

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+package com.baeldung.polymorphism;
+
+import static org.junit.Assert.*;
+
+import java.awt.image.BufferedImage;
+
+import org.junit.Ignore;
+import org.junit.Test;
+
+public class PolymorphismUnitTest {
+
+    @Test
+    public void givenImageFile_whenFileCreated_shouldSucceed() {
+        ImageFile imageFile = FileManager.createImageFile("SampleImageFile", 200, 100, new BufferedImage(100, 200, BufferedImage.TYPE_INT_RGB).toString()
+            .getBytes(), "v1.0.0");
+        assertEquals(200, imageFile.getHeight());
+    }
+
+    // Downcasting then Upcasting
+    @Test
+    public void givenTextFile_whenTextFileCreatedAndAssignedToGenericFileAndCastBackToTextFileOnGetWordCount_shouldSucceed() {
+        GenericFile textFile = FileManager.createTextFile("SampleTextFile", "This is a sample text content", "v1.0.0");
+        TextFile textFile2 = (TextFile) textFile;
+        assertEquals(6, textFile2.getWordCount());
+    }
+
+    // Downcasting
+    @Test(expected = ClassCastException.class)
+    public void givenGenericFile_whenCastToTextFileAndInvokeGetWordCount_shouldFail() {
+        GenericFile genericFile = new GenericFile();
+        TextFile textFile = (TextFile) genericFile;
+        System.out.println(textFile.getWordCount());
+    }
+}