Fixed issue #57 by replacing the use of java.util.Deque with java.util.LinkedList. I also added the animal-sniffer plugin to the Maven build to verify SDK compatibility.

Author: SQiShER

pom.xml

@@ -15,7 +15,8 @@
   ~ limitations under the License.
   -->
 
-<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
 
     <parent>
         <groupId>org.sonatype.oss</groupId>
@@ -81,7 +82,7 @@
             <plugin>
                 <artifactId>maven-release-plugin</artifactId>
                 <configuration>
-                    <scmCommentPrefix />
+                    <scmCommentPrefix/>
                 </configuration>
             </plugin>
             <plugin>
@@ -155,6 +156,35 @@
                     </execution>
                 </executions>
             </plugin>
+            <plugin>
+                <groupId>org.jvnet</groupId>
+                <artifactId>animal-sniffer</artifactId>
+                <version>1.2</version>
+                <executions>
+                    <execution>
+                        <id>animal-sniffer</id>
+                        <phase>compile</phase>
+                        <goals>
+                            <goal>check</goal>
+                        </goals>
+                        <configuration>
+                            <signature>
+                                <groupId>org.jvnet.animal-sniffer</groupId>
+                                <artifactId>java1.5</artifactId>
+                                <version>1.0</version>
+                            </signature>
+                        </configuration>
+                    </execution>
+                </executions>
+                <dependencies>
+                    <dependency>
+                        <groupId>org.jvnet.animal-sniffer</groupId>
+                        <artifactId>java1.5</artifactId>
+                        <version>1.0</version>
+                        <type>sig</type>
+                    </dependency>
+                </dependencies>
+            </plugin>
         </plugins>
         <pluginManagement>
             <plugins>

src/main/java/de/danielbechler/diff/CircularReferenceDetector.java

@@ -24,7 +24,12 @@
 /** @author Daniel Bechler */
 class CircularReferenceDetector
 {
-	private final Deque<Entry> stack = new LinkedList<Entry>();
+	/**
+	 * It would be better to use <code>java.util.Deque</code> instead of the linked list, but that was first
+	 * introduced in Java 6 and would break compatibility with Java 5.
+	 */
+	@SuppressWarnings("TypeMayBeWeakened")
+	private final LinkedList<Entry> stack = new LinkedList<Entry>();
 
 	private ReferenceMatchingMode referenceMatchingMode = ReferenceMatchingMode.EQUALITY_OPERATOR;