Merge pull request #10440 from sk1418/BAEL-2517_unchecked_conversion

BAEL-2517

core-java-modules/core-java-lang-oop-generics/pom.xml

@@ -13,4 +13,32 @@
     <name>core-java-lang-oop-generics</name>
     <packaging>jar</packaging>
 
+    <build>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven-compiler-plugin.version}</version>
+                <configuration>
+                    <source>${maven.compiler.source}</source>
+                    <target>${maven.compiler.target}</target>
+                    <compilerArguments>
+                        <Xlint:unchecked/>
+                    </compilerArguments>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+    <properties>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
+    </properties>
+
 </project>

core-java-modules/core-java-lang-oop-generics/src/main/java/com/baeldung/uncheckedconversion/UncheckedConversion.java

@@ -0,0 +1,45 @@
+package com.baeldung.uncheckedconversion;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Date;
+import java.util.List;
+
+public class UncheckedConversion {
+    public static List getRawList() {
+        List result = new ArrayList();
+        result.add("I am the 1st String.");
+        result.add("I am the 2nd String.");
+        result.add("I am the 3rd String.");
+        return result;
+    }
+
+    public static List getRawListWithMixedTypes() {
+        List result = new ArrayList();
+        result.add("I am the 1st String.");
+        result.add("I am the 2nd String.");
+        result.add("I am the 3rd String.");
+        result.add(new Date());
+        return result;
+    }
+
+    public static <T> List<T> castList(Class<? extends T> clazz, Collection<?> rawCollection) {
+        List<T> result = new ArrayList<>(rawCollection.size());
+        for (Object o : rawCollection) {
+            try {
+                result.add(clazz.cast(o));
+            } catch (ClassCastException e) {
+                // log the exception or other error handling
+            }
+        }
+        return result;
+    }
+
+    public static <T> List<T> castList2(Class<? extends T> clazz, Collection<?> rawCollection) throws ClassCastException {
+        List<T> result = new ArrayList<>(rawCollection.size());
+        for (Object o : rawCollection) {
+            result.add(clazz.cast(o));
+        }
+        return result;
+    }
+}

core-java-modules/core-java-lang-oop-generics/src/test/java/com/baeldung/uncheckedconversion/UncheckedConversionUnitTest.java

@@ -0,0 +1,39 @@
+package com.baeldung.uncheckedconversion;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.List;
+
+public class UncheckedConversionUnitTest {
+
+    @Test
+    public void givenRawList_whenAssignToTypedList_shouldHaveCompilerWarning() {
+        List<String> fromRawList = UncheckedConversion.getRawList();
+        Assert.assertEquals(3, fromRawList.size());
+        Assert.assertEquals("I am the 1st String.", fromRawList.get(0));
+    }
+
+    @Test(expected = ClassCastException.class)
+    public void givenRawList_whenListHasMixedType_shouldThrowClassCastException() {
+        List<String> fromRawList = UncheckedConversion.getRawListWithMixedTypes();
+        Assert.assertEquals(4, fromRawList.size());
+        Assert.assertFalse(fromRawList.get(3).endsWith("String."));
+    }
+
+    @Test
+    public void givenRawList_whenAssignToTypedListAfterCallingCastList_shouldOnlyHaveElementsWithExpectedType() {
+        List rawList = UncheckedConversion.getRawListWithMixedTypes();
+        List<String> strList = UncheckedConversion.castList(String.class, rawList);
+        Assert.assertEquals(4, rawList.size());
+        Assert.assertEquals("One element with the wrong type has been filtered out.", 3, strList.size());
+        Assert.assertTrue(strList.stream().allMatch(el -> el.endsWith("String.")));
+    }
+
+    @Test(expected = ClassCastException.class)
+    public void givenRawListWithWrongType_whenAssignToTypedListAfterCallingCastList2_shouldThrowException() {
+        List rawList = UncheckedConversion.getRawListWithMixedTypes();
+        UncheckedConversion.castList2(String.class, rawList);
+    }
+
+}