BAEL-922 Type Erasure Explained (#2100)

* 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

core-java/src/main/java/com/baeldung/typeerasure/ArrayContentPrintUtil.java

@@ -0,0 +1,16 @@
+package com.baeldung.typeerasure;
+
+public class ArrayContentPrintUtil {
+
+   public static <E> void printArray(E[] array) {
+        for (E element : array) {
+            System.out.printf("%s ", element);
+        }
+    }
+    
+    public static <E extends Comparable<E>> void printArray(E[] array) {
+        for (E element : array) {
+            System.out.printf("%s ", element);
+        }
+    }
+}

core-java/src/main/java/com/baeldung/typeerasure/BoundStack.java

@@ -0,0 +1,37 @@
+package com.baeldung.typeerasure;
+
+import java.util.Arrays;
+
+public class BoundStack<E extends Comparable<E>> {
+
+    private E[] stackContent;
+    private int total;
+
+    public BoundStack(int capacity) {
+        this.stackContent = (E[]) new Object[capacity];
+    }
+
+    public void push(E data) {
+        if (total == stackContent.length) {
+            resize(2 * stackContent.length);
+        }
+        stackContent[total++] = data;
+    }
+
+    public E pop() {
+        if (!isEmpty()) {
+            E datum = stackContent[total];
+            stackContent[total--] = null;
+            return datum;
+        }
+        return null;
+    }
+
+    private void resize(int capacity) {
+        Arrays.copyOf(stackContent, capacity);
+    }
+
+    public boolean isEmpty() {
+        return total == 0;
+    }
+}

core-java/src/main/java/com/baeldung/typeerasure/IntegerStack.java

@@ -0,0 +1,13 @@
+package com.baeldung.typeerasure;
+
+public class IntegerStack extends Stack<Integer> {
+
+    public IntegerStack(int capacity) {
+        super(capacity);
+    }
+
+    public void push(Integer value) {
+        System.out.println("Pushing into my integerStack");
+        super.push(value);
+    }
+}

core-java/src/main/java/com/baeldung/typeerasure/Stack.java

@@ -0,0 +1,39 @@
+package com.baeldung.typeerasure;
+
+import java.util.Arrays;
+
+public class Stack<E> {
+
+    private E[] stackContent;
+    private int total;
+
+    public Stack(int capacity) {
+        this.stackContent = (E[]) new Object[capacity];
+    }
+
+    public void push(E data) {
+        System.out.println("In base stack push#");
+        if (total == stackContent.length) {
+            resize(2 * stackContent.length);
+        }
+        stackContent[total++] = data;
+    }
+
+    public E pop() {
+        if (!isEmpty()) {
+            E datum = stackContent[total];
+            stackContent[total--] = null;
+            return datum;
+        }
+        return null;
+    }
+
+    private void resize(int capacity) {
+        Arrays.copyOf(stackContent, capacity);
+    }
+
+    public boolean isEmpty() {
+        return total == 0;
+    }
+
+}

core-java/src/test/java/com/baeldung/typeerasure/TypeErasureUnitTest.java

@@ -0,0 +1,21 @@
+package com.baeldung.typeerasure;
+
+import org.junit.Test;
+
+public class TypeErasureUnitTest {
+
+    @Test(expected = ClassCastException.class)
+    public void givenIntegerStack_whenStringPushedAndAssignPoppedValueToInteger_shouldFail() {
+        IntegerStack integerStack = new IntegerStack(5);
+        Stack stack = integerStack;
+        stack.push("Hello");
+        Integer data = integerStack.pop();
+    }
+
+    @Test
+    public void givenAnyArray_whenInvokedPrintArray_shouldSucceed() {
+        Integer[] scores = new Integer[] { 100, 200, 10, 99, 20 };
+        ArrayContentPrintUtil.printArray(scores);
+    }
+
+}