HashSets for starters.

src/engine/ConfigParsing/EffectEntry/EffectEntry.java

@@ -0,0 +1,12 @@
+package engine.ConfigParsing.EffectEntry;
+
+import java.util.HashSet;
+
+public class EffectEntry {
+    public String id;
+    public String name;
+    public int icon;
+    public HashSet<String> sources;
+    public HashSet<String> mods;
+    public HashSet<String> conditions;
+}