#237 Modernize codebase towards modern Java (#240)

- applies several migration aids to modernize existing code towards Java 11
- fixes C-style array declarations
- declares several fields as `final` where applicable
- collapses / merges identical catch blocks
- reduces use of deprecated API (mostly Hibernate)
- reduces use of generic classes without type parameters
- simplifies unnecessary String conversions
- removes redundant initializers
- removes unnecessary modifiers of methods declared in interfaces
- removes unnecessary semicolons
- removes unnecessary toString() invocations

dkpro-jwpl-api/src/it/java/org/dkpro/jwpl/api/PerformanceIT.java

@@ -30,8 +30,6 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import static org.junit.Assert.fail;
-
 public class PerformanceIT implements WikiConstants {
 
     private static final Logger logger = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());

dkpro-jwpl-api/src/it/java/org/dkpro/jwpl/api/PerformanceTest.java

@@ -37,15 +37,15 @@ class PerformanceTest {
 
     private static final Logger logger = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
 
-    private Wikipedia wiki;
+    private final Wikipedia wiki;
 
     private final Set<Integer> pageIDs;
     private List<List<Integer>> randomIdList;
     private List<List<String>> randomTitleList;
 
     // determines how many sample pageCycles are run for averaging results
-    private int maxiCycles;
-    private int pageCycles;
+    private final int maxiCycles;
+    private final int pageCycles;
 
     PerformanceTest(Wikipedia pWiki, int maxiCycles, int pageCycles) throws WikiApiException {
         this.wiki = pWiki;
@@ -112,8 +112,8 @@ void loadPagesAndAccessFieldsTest(String mode) throws WikiApiException {
             for (int i=0; i<pageCycles; i++) {
 
                 Set<Integer> page = GraphUtilities.getRandomPageSubset(pageIDs, 1);
-                Iterator it = page.iterator();
-                int pageID = (Integer) it.next();
+                Iterator<Integer> it = page.iterator();
+                int pageID = it.next();
                 long id = wiki.__getPageHibernateId(pageID);
 
                 double startTime = System.currentTimeMillis();
@@ -172,7 +172,7 @@ private void loadPageAndAccessFields_extern(long id) throws WikiApiException {
      * certain number of pages in order to gain efficiency.
      * We get the same number of pages from a Wikipedia using
      * different buffer sizes and return the performance.
-     *
+     * <p>
      * For an unbuffered iterator set bufferSize to 1.
      */
     void loadPageAndIterate(int numberOfPages, int bufferSize, Wikipedia wiki) {

dkpro-jwpl-api/src/main/java/org/dkpro/jwpl/api/Category.java

@@ -31,9 +31,9 @@
 
 public class Category implements WikiConstants {
 
-    private CategoryDAO catDAO;
+    private final CategoryDAO catDAO;
     private org.dkpro.jwpl.api.hibernate.Category hibernateCategory;
-    private Wikipedia wiki;
+    private final Wikipedia wiki;
 
 
     /**
@@ -105,13 +105,13 @@ private void createCategory(Title title) throws WikiPageNotFoundException {
         Session session = this.wiki.__getHibernateSession();
         session.beginTransaction();
 
-        Object returnValue;
+        Integer returnValue;
 
         String query = "select cat.pageId from Category as cat where cat.name = :name";
         if(wiki.getDatabaseConfiguration().supportsCollation()) {
             query += Wikipedia.SQL_COLLATION;
         }
-        returnValue = session.createNativeQuery(query)
+        returnValue = session.createNativeQuery(query, Integer.class)
                 .setParameter("name", name, StandardBasicTypes.STRING)
                 .uniqueResult();
         session.getTransaction().commit();
@@ -122,8 +122,7 @@ private void createCategory(Title title) throws WikiPageNotFoundException {
             throw new WikiPageNotFoundException("No category with name " + name + " was found.");
         }
         else {
-            // now cast it into an integer
-            int pageID = (Integer) returnValue;
+            int pageID = returnValue;
             createCategory( pageID);
         }
     }
@@ -164,10 +163,10 @@ public Set<Category> getParents() {
         Session session = this.wiki.__getHibernateSession();
         session.beginTransaction();
         session.lock(hibernateCategory, LockMode.NONE);
-        Set<Integer> tmpSet = new HashSet<Integer>(hibernateCategory.getInLinks());
+        Set<Integer> tmpSet = new HashSet<>(hibernateCategory.getInLinks());
         session.getTransaction().commit();
 
-        Set<Category> categories = new HashSet<Category>();
+        Set<Category> categories = new HashSet<>();
         for (int pageID : tmpSet) {
             categories.add(this.wiki.getCategory(pageID));
         }
@@ -184,13 +183,14 @@ public int getNumberOfParents() {
         long id = this.__getId();
         Session session = this.wiki.__getHibernateSession();
         session.beginTransaction();
-        Object returnValue = session.createNativeQuery("select count(inLinks) from category_inlinks where id = :id")
+        String sql = "select count(inLinks) from category_inlinks where id = :id";
+        Long returnValue = session.createNativeQuery(sql, Long.class)
             .setParameter("id", id, StandardBasicTypes.LONG)
             .uniqueResult();
         session.getTransaction().commit();
 
         if (returnValue != null) {
-            nrOfInlinks = ((Long) returnValue).intValue();
+            nrOfInlinks = returnValue.intValue();
         }
         return nrOfInlinks;
     }
@@ -202,7 +202,7 @@ public Set<Integer> getParentIDs() {
         Session session = this.wiki.__getHibernateSession();
         session.beginTransaction();
         session.lock(hibernateCategory, LockMode.NONE);
-        Set<Integer> tmpSet = new HashSet<Integer>(hibernateCategory.getInLinks());
+        Set<Integer> tmpSet = new HashSet<>(hibernateCategory.getInLinks());
         session.getTransaction().commit();
         return tmpSet;
     }
@@ -214,10 +214,10 @@ public Set<Category> getChildren() {
         Session session = this.wiki.__getHibernateSession();
         session.beginTransaction();
         session.lock(hibernateCategory, LockMode.NONE);
-        Set<Integer> tmpSet = new HashSet<Integer>(hibernateCategory.getOutLinks());
+        Set<Integer> tmpSet = new HashSet<>(hibernateCategory.getOutLinks());
         session.getTransaction().commit();
 
-        Set<Category> categories = new HashSet<Category>();
+        Set<Category> categories = new HashSet<>();
         for (int pageID : tmpSet) {
             categories.add(this.wiki.getCategory(pageID));
         }
@@ -234,13 +234,14 @@ public int getNumberOfChildren() {
         long id = this.__getId();
         Session session = this.wiki.__getHibernateSession();
         session.beginTransaction();
-        Object returnValue = session.createNativeQuery("select count(outLinks) from category_outlinks where id = :id")
+        String sql = "select count(outLinks) from category_outlinks where id = :id";
+        Long returnValue = session.createNativeQuery(sql, Long.class)
             .setParameter("id", id, StandardBasicTypes.LONG)
             .uniqueResult();
         session.getTransaction().commit();
 
         if (returnValue != null) {
-            nrOfOutlinks = ((Long) returnValue).intValue();
+            nrOfOutlinks = returnValue.intValue();
         }
         return nrOfOutlinks;
     }
@@ -252,7 +253,7 @@ public Set<Integer> getChildrenIDs() {
         Session session = this.wiki.__getHibernateSession();
         session.beginTransaction();
         session.lock(hibernateCategory, LockMode.NONE);
-        Set<Integer> tmpSet = new HashSet<Integer>(hibernateCategory.getOutLinks());
+        Set<Integer> tmpSet = new HashSet<>(hibernateCategory.getOutLinks());
         session.getTransaction().commit();
         return tmpSet;
     }
@@ -277,7 +278,7 @@ public Title getTitle() throws WikiTitleParsingException  {
      */
     public Set<Page> getArticles() throws WikiApiException {
         Set<Integer> tmpSet = getArticleIds();
-        Set<Page> pages = new HashSet<Page>();
+        Set<Page> pages = new HashSet<>();
         for (int pageID : tmpSet) {
             pages.add(this.wiki.getPage(pageID));
         }
@@ -291,7 +292,7 @@ public Set<Integer> getArticleIds() {
         Session session = this.wiki.__getHibernateSession();
         session.beginTransaction();
         session.lock(hibernateCategory, LockMode.NONE);
-        Set<Integer> tmpSet = new HashSet<Integer>(hibernateCategory.getPages());
+        Set<Integer> tmpSet = new HashSet<>(hibernateCategory.getPages());
         session.getTransaction().commit();
 
         return tmpSet;
@@ -307,13 +308,14 @@ public int getNumberOfPages() {
         long id = this.__getId();
         Session session = this.wiki.__getHibernateSession();
         session.beginTransaction();
-        Object returnValue = session.createNativeQuery("select count(pages) from category_pages where id = :id")
+        String sql = "select count(pages) from category_pages where id = :id";
+        Long returnValue = session.createNativeQuery(sql, Long.class)
             .setParameter("id", id, StandardBasicTypes.LONG)
             .uniqueResult();
         session.getTransaction().commit();
 
         if (returnValue != null) {
-            nrOfPages = ((Long) returnValue).intValue();
+            nrOfPages = returnValue.intValue();
         }
         return nrOfPages;
     }
@@ -352,7 +354,7 @@ protected Iterable <Category> getDescendants(int bufferSize) {
      * @return Returns the siblings of this category or null, if there are none.
      */
     public Set<Category> getSiblings() {
-        Set<Category> siblings = new HashSet<Category>();
+        Set<Category> siblings = new HashSet<>();
 
         // add siblings
         for (Category parent : this.getParents()) {

dkpro-jwpl-api/src/main/java/org/dkpro/jwpl/api/CategoryDescendantsIterable.java

@@ -26,8 +26,8 @@
  */
 public class CategoryDescendantsIterable implements Iterable<Category> {
 
-    private Wikipedia wiki;
-    private Category startCategory;
+    private final Wikipedia wiki;
+    private final Category startCategory;
 
     /**
      * The size of the page buffer.

dkpro-jwpl-api/src/main/java/org/dkpro/jwpl/api/CategoryDescendantsIterator.java

@@ -37,26 +37,26 @@ public class CategoryDescendantsIterator implements Iterator<Category> {
 
     private final Logger logger = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
 
-    private Wikipedia wiki;
+    private final Wikipedia wiki;
 
-    private CategoryBuffer buffer;
+    private final CategoryBuffer buffer;
 
     /** Contains all category ids that have not been expanded, yet. */
-    private Set<Integer> notExpandedCategories;
+    private final Set<Integer> notExpandedCategories;
 
     /** As we do not inspect the whole graph at once now, we need a way to check whether a node was already expanded, to avoid infinite loops. */
-    private Set<Integer> expandedCategoryIds;
+    private final Set<Integer> expandedCategoryIds;
 
     public CategoryDescendantsIterator(Wikipedia wiki, int bufferSize, Category startCategory) {
         this.wiki = wiki;
         buffer = new CategoryBuffer(bufferSize);
-        notExpandedCategories = new HashSet<Integer>();
+        notExpandedCategories = new HashSet<>();
         // initialize with children of start category
         for (Category catItem : startCategory.getChildren()) {
             notExpandedCategories.add(catItem.getPageId());
         }
 
-        expandedCategoryIds = new HashSet<Integer>();
+        expandedCategoryIds = new HashSet<>();
     }
 
     public boolean hasNext(){
@@ -78,15 +78,15 @@ public void remove() {
      */
     class CategoryBuffer{
 
-        private List<Category> buffer;
-        private int maxBufferSize;  // the number of pages to be buffered after a query to the database.
+        private final List<Category> buffer;
+        private final int maxBufferSize;  // the number of pages to be buffered after a query to the database.
         private int bufferFillSize; // even a 500 slot buffer can be filled with only 5 elements
         private int bufferOffset;   // the offset in the buffer
         private int dataOffset;     // the overall offset in the data
 
         public CategoryBuffer(int bufferSize){
             this.maxBufferSize = bufferSize;
-            this.buffer = new ArrayList<Category>();
+            this.buffer = new ArrayList<>();
             this.bufferFillSize = 0;
             this.bufferOffset = 0;
             this.dataOffset = 0;
@@ -142,7 +142,7 @@ private boolean fillBuffer() {
             bufferOffset = 0;
             bufferFillSize = 0;
 
-            List<Integer> queue = new LinkedList<Integer>();
+            List<Integer> queue = new LinkedList<>();
 
             // add not expanded categories to queue
             queue.addAll(notExpandedCategories);