util: use generics for Loader.getClassInstance(s) methods

Author: mbtaylor

table/src/main/uk/ac/starlink/table/StoragePolicy.java

@@ -57,9 +57,11 @@ public abstract class StoragePolicy {
 
     /**
      * Name of the system property which can be set to indicate the
-     * initial setting of the default storage policy.
+     * initial setting of the default storage policy ({@value}).
      * Currently recognised values are "adaptive", "memory", "disk",
      * "sideways", and "discard".
+     * Alternatively, the classname of a StoragePolicy implementation
+     * with a no-arg constructor may be supplied.
      */
     public static final String PREF_PROPERTY = "startable.storage";
 
@@ -89,7 +91,6 @@ else if ( "discard".equals( pref ) ) {
                 }
                 else {
                     StoragePolicy named =
-                        (StoragePolicy) 
                         Loader.getClassInstance( pref, StoragePolicy.class );
                     defaultInstance_ = named != null 
                                      ? named

topcat/src/main/uk/ac/starlink/topcat/ControlWindow.java

@@ -603,10 +603,9 @@ public void mouseClicked( MouseEvent evt ) {
             toolBar.add( interopAct );
         }
         toolBar.add( MethodWindow.getWindowAction( this, false ) );
-        List actList = Loader.getClassInstances( TOPCAT_TOOLS_PROP,
-                                                 TopcatToolAction.class );
-        for ( Iterator it = actList.iterator(); it.hasNext(); ) {
-            TopcatToolAction tact = (TopcatToolAction) it.next();
+        for ( TopcatToolAction tact :
+              Loader.getClassInstances( TOPCAT_TOOLS_PROP,
+                                        TopcatToolAction.class ) ) {
             tact.setParent( this );
             toolBar.add( tact );
         }

topcat/src/main/uk/ac/starlink/topcat/LoadWindow.java

@@ -132,7 +132,6 @@ public TableLoader createTableLoader() {
         /* Prepare actions for all known dialogues. */
         actList_ = new ArrayList<Action>();
         knownDialogs_ =
-            (TableLoadDialog[])
             Loader.getClassInstances( DIALOG_CLASSES, LOAD_DIALOGS_PROPERTY,
                                       TableLoadDialog.class )
            .toArray( new TableLoadDialog[ 0 ] );

ttools/src/main/uk/ac/starlink/ttools/join/MatchEngineParameter.java

@@ -498,9 +498,7 @@ else if ( cName.equalsIgnoreCase( "htm" ) ) {
                                                      ARC_SECOND );
             }
             else {
-                component =
-                    (MatchEngine) Loader.getClassInstance( cName,
-                                                           MatchEngine.class );
+                component = Loader.getClassInstance( cName, MatchEngine.class );
                 if ( component == null ) {
                     throw new UsageException( "Unknown matcher element: "
                                             + cName );

util/src/main/uk/ac/starlink/util/Loader.java

@@ -252,7 +252,7 @@ public static synchronized void loadProperties() {
      *                 from
      * @return  new <tt>className</tt> instance, or <tt>null</tt>
      */
-    public static Object getClassInstance( String className, Class type ) {
+    public static <T> T getClassInstance( String className, Class<T> type ) {
         if ( className == null || className.trim().length() == 0 ) {
             return null;
         }
@@ -277,7 +277,7 @@ public static Object getClassInstance( String className, Class type ) {
             return null;
         }
         try {
-            return clazz.newInstance();
+            return type.cast( clazz.newInstance() );
         }
         catch ( ExceptionInInitializerError e ) {
             warn( e.getCause() + " loading class " + className );
@@ -304,8 +304,9 @@ public static Object getClassInstance( String className, Class type ) {
      * @param   type   class which instantiated classes must be assignable from
      * @return  list of new <tt>type</tt> instances (may be empty, but not null)
      */
-    public static List getClassInstances( String propertyName, Class type ) {
-        List instances = new ArrayList();
+    public static <T> List<T> getClassInstances( String propertyName,
+                                                 Class<T> type ) {
+        List<T> instances = new ArrayList<T>();
 
         /* Get the property value, if possible. */
         String propVal;
@@ -323,7 +324,7 @@ public static List getClassInstances( String propertyName, Class type ) {
         for ( StringTokenizer stok = new StringTokenizer( propVal, ":" );
               stok.hasMoreElements(); ) {
             String cname = stok.nextToken().trim();
-            Object inst = getClassInstance( cname, type );
+            T inst = getClassInstance( cname, type );
             if ( inst != null ) {
                 instances.add( inst );
             }
@@ -342,12 +343,13 @@ public static List getClassInstances( String propertyName, Class type ) {
      *
      * @param  defaultNames  array of string
      */
-    public static List getClassInstances( String[] defaultNames, 
-                                          String propertyName, Class type ) {
+    public static <T> List<T> getClassInstances( String[] defaultNames, 
+                                                 String propertyName,
+                                                 Class<T> type ) {
         Loader.loadProperties();
-        List instances = new ArrayList();
+        List<T> instances = new ArrayList<T>();
         for ( int i = 0; i < defaultNames.length; i++ ) {
-            Object instance = getClassInstance( defaultNames[ i ], type );
+            T instance = getClassInstance( defaultNames[ i ], type );
             if ( instance != null ) {
                 instances.add( instance );
             }

votable/src/main/uk/ac/starlink/votable/Namespacing.java

@@ -136,8 +136,7 @@ public static Namespacing getInstance() {
                 }
             }
             if ( ns == null ) {
-                ns = (Namespacing)
-                     Loader.getClassInstance( policy, Namespacing.class );
+                ns = Loader.getClassInstance( policy, Namespacing.class );
             }
             if ( ns == null ) {
                 StringBuffer sbuf = new StringBuffer()