Code cleanup

src/main/java/io/github/apickledwalrus/skriptplaceholders/SkriptPlaceholders.java

@@ -13,10 +13,7 @@ public class SkriptPlaceholders extends JavaPlugin {
 	@Override
 	public void onEnable() {
 		instance = this;
-		for (PlaceholderPlugin plugin : PlaceholderPlugin.values()) {
-			if (plugin.isInstalled()) {
-				break;
-			}
+		if (PlaceholderPlugin.getInstalledPlugins().isEmpty()) {
 			getLogger().severe("No placeholder plugins were found. Do you have any installed? Disabling...");
 			getServer().getPluginManager().disablePlugin(this);
 			return;

src/main/java/io/github/apickledwalrus/skriptplaceholders/placeholder/PlaceholderPlugin.java

@@ -6,6 +6,10 @@
 import org.bukkit.OfflinePlayer;
 import org.jetbrains.annotations.Nullable;
 
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.stream.Collectors;
+
 /**
  * A utility enum for the placeholder plugins.
  */
@@ -71,6 +75,17 @@ public PlaceholderListener registerPlaceholder(PlaceholderEvaluator evaluator, S
 		}
 	};
 
+	private static final Collection<PlaceholderPlugin> INSTALLED_PLUGINS = Arrays.stream(values())
+			.filter(PlaceholderPlugin::isInstalled)
+			.collect(Collectors.toSet());
+
+	/**
+	 * @return A list of all installed placeholder plugins.
+	 */
+	public static Collection<PlaceholderPlugin> getInstalledPlugins() {
+		return INSTALLED_PLUGINS;
+	}
+
 	private final String displayName;
 	private final boolean installed;
 

src/main/java/io/github/apickledwalrus/skriptplaceholders/skript/elements/ExprParsePlaceholder.java

@@ -53,13 +53,11 @@ public boolean init(Expression<?>[] exprs, int matchedPattern, @NotNull Kleenean
 	@Override
 	protected String @NotNull [] get(@NotNull Event event) {
 		List<String> values = new ArrayList<>();
-
-		for (OfflinePlayer player : players != null ? players.getArray(event) : new OfflinePlayer[]{null}) {
-			for (String placeholder : placeholders.getArray(event)) {
-				for (PlaceholderPlugin plugin : PlaceholderPlugin.values()) {
-					if (!plugin.isInstalled()) {
-						continue;
-					}
+		String[] placeholders = this.placeholders.getArray(event);
+		OfflinePlayer[] players = this.players != null ? this.players.getArray(event) : new OfflinePlayer[]{null};
+		for (OfflinePlayer player : players) {
+			for (String placeholder : placeholders) {
+				for (PlaceholderPlugin plugin : PlaceholderPlugin.getInstalledPlugins()) {
 					String value = plugin.parsePlaceholder(placeholder, player);
 					if (value != null) {
 						values.add(value);
@@ -68,13 +66,12 @@ public boolean init(Expression<?>[] exprs, int matchedPattern, @NotNull Kleenean
 				}
 			}
 		}
-
 		return values.toArray(new String[0]);
 	}
 
 	@Override
 	public boolean isSingle() {
-		return players != null ? (placeholders.isSingle() && players.isSingle()) : placeholders.isSingle();
+		return placeholders.isSingle() && (players == null || players.isSingle());
 	}
 
 	@Override

src/main/java/io/github/apickledwalrus/skriptplaceholders/skript/elements/ExprPlaceholder.java

@@ -57,13 +57,18 @@ public boolean init(Expression<?> @NotNull [] exprs, int matchedPattern, @NotNul
 
 	@Override
 	protected String @NotNull [] get(@NotNull Event event) {
+		if (!(event instanceof PlaceholderEvent))
+			return new String[0];
+		PlaceholderEvent placeholderEvent = (PlaceholderEvent) event;
 		switch (part) {
 			case PLACEHOLDER:
-				return new String[]{((PlaceholderEvent) event).getPlaceholder()};
+				return new String[]{placeholderEvent.getPlaceholder()};
 			case PREFIX:
-				return new String[]{((PlaceholderEvent) event).getPrefix()};
+				String prefix = placeholderEvent.getPrefix();
+				return prefix != null ? new String[]{prefix} : new String[0];
 			case IDENTIFIER:
-				return new String[]{((PlaceholderEvent) event).getIdentifier()};
+				String identifier = placeholderEvent.getIdentifier();
+				return identifier != null ? new String[]{identifier} : new String[0];
 			default:
 				throw new IllegalArgumentException("Unable to handle PlaceholderPart: " + part);
 		}