DefaultScriptInterpreter: improve constructors

The old constructor is deprecated.

There is now a simple constructor taking only the ScriptLanguage,
as well as one which allows to manually override the ScriptEngine.

The SciJava application context is derived from the ScriptLanguage,
and services (notably: the PrefService) are injected from there.

The PrefService is now optional, and when it is null, there is no
history available. (The code for null History was already in place
everywhere -- it just couldn't happen previously due to the explicit
"new History" call in the constructor. So now we make use of it.)

Author: ctrueden

src/main/java/org/scijava/script/DefaultScriptInterpreter.java

@@ -46,21 +46,50 @@ public class DefaultScriptInterpreter implements ScriptInterpreter {
 	private final ScriptEngine engine;
 	private final History history;
 
+	@Parameter(required = false)
+	private PrefService prefs;
+
 	/**
-	 * Constructs a new {@link DefaultScriptInterpreter}.
-	 * 
-	 * @param scriptService the script service
-	 * @param language the script language
+	 * @deprecated Use {@link #DefaultScriptInterpreter(ScriptLanguage)} instead.
 	 */
+	@Deprecated
+	@SuppressWarnings("unused")
 	public DefaultScriptInterpreter(final PrefService prefs,
 		final ScriptService scriptService, final ScriptLanguage language)
 	{
+		this(language);
+	}
+
+	/**
+	 * Creates a new script interpreter for the given script language.
+	 * 
+	 * @param language {@link ScriptLanguage} of the interpreter
+	 */
+	public DefaultScriptInterpreter(final ScriptLanguage language) {
+		this(language, null);
+	}
+
+	/**
+	 * Creates a new script interpreter for the given script language, using the
+	 * specified script engine.
+	 * 
+	 * @param language {@link ScriptLanguage} of the interpreter
+	 * @param engine {@link ScriptEngine} to use, or null for the specified
+	 *          language's default engine
+	 */
+	public DefaultScriptInterpreter(final ScriptLanguage language,
+		final ScriptEngine engine)
+	{
+		language.getContext().inject(this);
 		this.language = language;
-		engine = language.getScriptEngine();
-		history = new History(prefs, engine.getClass().getName());
+		this.engine = engine == null ? language.getScriptEngine() : engine;
+		history = prefs == null ? null :
+			new History(prefs, this.engine.getClass().getName());
 		readHistory();
 	}
 
+	// -- ScriptInterpreter methods --
+
 	@Override
 	public synchronized void readHistory() {
 		if (history == null) return;