#1067: Add method to get Advancement requirements

src/main/java/org/bukkit/advancement/Advancement.java

@@ -19,6 +19,14 @@ public interface Advancement extends Keyed {
     @NotNull
     Collection<String> getCriteria();
 
+    /**
+     * Returns the requirements for this advancement.
+     *
+     * @return an AdvancementRequirements object.
+     */
+    @NotNull
+    AdvancementRequirements getRequirements();
+
     /**
      * Returns the display information for this advancement.
      *

src/main/java/org/bukkit/advancement/AdvancementRequirement.java

@@ -0,0 +1,23 @@
+package org.bukkit.advancement;
+
+import java.util.List;
+import org.jetbrains.annotations.NotNull;
+
+public interface AdvancementRequirement {
+
+    /**
+     * Get all required criteria.
+     *
+     * @return the list of required criteria for this requirement.
+     */
+    @NotNull
+    List<String> getRequiredCriteria();
+
+    /**
+     * Check if the requirement is strict.
+     *
+     * @return true if requirement list contains one criteria, false if
+     * multiple.
+     */
+    boolean isStrict();
+}

src/main/java/org/bukkit/advancement/AdvancementRequirements.java

@@ -0,0 +1,26 @@
+package org.bukkit.advancement;
+
+import java.util.List;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * The list of requirements for the advancement.
+ *
+ * Requirements are complimentary to criteria. They are just lists that contain
+ * more lists, which in turn contains strings that equal the names of the
+ * criteria. Ultimately defining the logic around how criteria are completed in
+ * order to grant the advancement.
+ *
+ * @see <a href=https://minecraft.wiki/w/Advancement_definition>Advancement Definition</a>
+ * @see <a href=https://www.minecraftforum.net/forums/minecraft-java-edition/redstone-discussion-and/commands-command-blocks-and/2809368-1-12-custom-advancements-aka-achievements#Requirements>Advancement Requirements</a>
+ */
+public interface AdvancementRequirements {
+
+    /**
+     * Get all the requirements present in this advancement.
+     *
+     * @return an unmodifiable copy of all requirements.
+     */
+    @NotNull
+    List<AdvancementRequirement> getRequirements();
+}