Improved some documentation and added some nullability annotations in database code

src/main/java/world/bentobox/bentobox/database/DatabaseConnector.java

@@ -1,9 +1,9 @@
 package world.bentobox.bentobox.database;
 
+import org.eclipse.jdt.annotation.NonNull;
+
 /**
- *
  * Creates a connection to a database.
- *
  */
 public interface DatabaseConnector {
 
@@ -28,13 +28,16 @@ public interface DatabaseConnector {
 
     /**
      * Looks through the database (or files) and returns a known unique key
+     *
      * @param tableName - name of the table
      * @return a unique key for this record
      */
+    @NonNull
     String getUniqueId(String tableName);
 
     /**
      * Check if a key exists in the database in this table or not
+     *
      * @param tableName - name of the table
      * @param key       - key to check
      * @return true if it exists

src/main/java/world/bentobox/bentobox/database/json/JSONDatabase.java

@@ -6,6 +6,9 @@ import world.bentobox.bentobox.database.DatabaseSetup;
 
 public class JSONDatabase implements DatabaseSetup {
 
+    /* (non-Javadoc)
+     * @see world.bentobox.bentobox.database.DatabaseSetup#getHandler(java.lang.Class)
+     */
     @Override
     public <T> AbstractDatabaseHandler<T> getHandler(Class<T> dataObjectClass) {
         return new JSONDatabaseHandler<>(BentoBox.getInstance(), dataObjectClass, new JSONDatabaseConnector(BentoBox.getInstance()));

src/main/java/world/bentobox/bentobox/database/json/JSONDatabaseConnector.java

@@ -3,6 +3,7 @@ package world.bentobox.bentobox.database.json;
 import java.io.File;
 import java.util.UUID;
 
+import org.eclipse.jdt.annotation.NonNull;
 import world.bentobox.bentobox.BentoBox;
 import world.bentobox.bentobox.database.DatabaseConnector;
 
@@ -18,6 +19,7 @@ public class JSONDatabaseConnector implements DatabaseConnector {
     }
 
     @Override
+    @NonNull
     public String getUniqueId(String tableName) {
         UUID uuid = UUID.randomUUID();
         File file = new File(dataFolder, tableName + File.separator + uuid.toString() + JSON);

src/main/java/world/bentobox/bentobox/database/mariadb/MariaDBDatabase.java

@@ -12,7 +12,7 @@ import world.bentobox.bentobox.database.DatabaseSetup;
 public class MariaDBDatabase implements DatabaseSetup {
 
     /* (non-Javadoc)
-     * @see world.bentobox.bentobox.database.BSBDbSetup#getHandler(java.lang.Class)
+     * @see world.bentobox.bentobox.database.DatabaseSetup#getHandler(java.lang.Class)
      */
     @Override
     public <T> AbstractDatabaseHandler<T> getHandler(Class<T> type) {

src/main/java/world/bentobox/bentobox/database/mariadb/MariaDBDatabaseConnector.java

@@ -6,6 +6,7 @@ import java.sql.SQLException;
 
 import org.bukkit.Bukkit;
 
+import org.eclipse.jdt.annotation.NonNull;
 import world.bentobox.bentobox.database.DatabaseConnectionSettingsImpl;
 import world.bentobox.bentobox.database.DatabaseConnector;
 
@@ -45,6 +46,7 @@ public class MariaDBDatabaseConnector implements DatabaseConnector {
     }
 
     @Override
+    @NonNull
     public String getUniqueId(String tableName) {
         // Not used
         return "";

src/main/java/world/bentobox/bentobox/database/mongodb/MongoDBDatabase.java

@@ -9,6 +9,9 @@ import world.bentobox.bentobox.database.DatabaseSetup;
 
 public class MongoDBDatabase implements DatabaseSetup {
 
+    /* (non-Javadoc)
+     * @see world.bentobox.bentobox.database.DatabaseSetup#getHandler(java.lang.Class)
+     */
     @Override
     public <T> AbstractDatabaseHandler<T> getHandler(Class<T> type) {
         BentoBox plugin = BentoBox.getInstance();

src/main/java/world/bentobox/bentobox/database/mongodb/MongoDBDatabaseConnector.java

@@ -6,6 +6,7 @@ import com.mongodb.MongoCredential;
 import com.mongodb.ServerAddress;
 import com.mongodb.client.MongoDatabase;
 
+import org.eclipse.jdt.annotation.NonNull;
 import world.bentobox.bentobox.database.DatabaseConnectionSettingsImpl;
 import world.bentobox.bentobox.database.DatabaseConnector;
 
@@ -38,6 +39,7 @@ public class MongoDBDatabaseConnector implements DatabaseConnector {
     }
 
     @Override
+    @NonNull
     public String getUniqueId(String tableName) {
         // Not used
         return "";

src/main/java/world/bentobox/bentobox/database/mysql/MySQLDatabase.java

@@ -7,9 +7,8 @@ import world.bentobox.bentobox.database.DatabaseSetup;
 
 public class MySQLDatabase implements DatabaseSetup {
 
-
     /* (non-Javadoc)
-     * @see world.bentobox.bentobox.database.BSBDbSetup#getHandler(java.lang.Class)
+     * @see world.bentobox.bentobox.database.DatabaseSetup#getHandler(java.lang.Class)
      */
     @Override
     public <T> AbstractDatabaseHandler<T> getHandler(Class<T> type) {

src/main/java/world/bentobox/bentobox/database/mysql/MySQLDatabaseConnector.java

@@ -6,6 +6,7 @@ import java.sql.SQLException;
 
 import org.bukkit.Bukkit;
 
+import org.eclipse.jdt.annotation.NonNull;
 import world.bentobox.bentobox.database.DatabaseConnectionSettingsImpl;
 import world.bentobox.bentobox.database.DatabaseConnector;
 
@@ -41,6 +42,7 @@ public class MySQLDatabaseConnector implements DatabaseConnector {
     }
 
     @Override
+    @NonNull
     public String getUniqueId(String tableName) {
         // Not used
         return "";

src/main/java/world/bentobox/bentobox/database/yaml/YamlDatabase.java

@@ -16,6 +16,9 @@ public class YamlDatabase implements DatabaseSetup {
         return new ConfigHandler<>(BentoBox.getInstance(), type, new YamlDatabaseConnector(BentoBox.getInstance()));
     }
 
+    /* (non-Javadoc)
+     * @see world.bentobox.bentobox.database.DatabaseSetup#getHandler(java.lang.Class)
+     */
     @Override
     public <T> AbstractDatabaseHandler<T> getHandler(Class<T> type) {
         return new YamlDatabaseHandler<>(BentoBox.getInstance(), type, new YamlDatabaseConnector(BentoBox.getInstance()));

src/main/java/world/bentobox/bentobox/database/yaml/YamlDatabaseConnector.java

@@ -27,6 +27,7 @@ import org.bukkit.configuration.file.YamlConfiguration;
 
 import com.google.common.base.Charsets;
 
+import org.eclipse.jdt.annotation.NonNull;
 import world.bentobox.bentobox.BentoBox;
 import world.bentobox.bentobox.database.DatabaseConnector;
 
@@ -191,6 +192,7 @@ public class YamlDatabaseConnector implements DatabaseConnector {
     }
 
     @Override
+    @NonNull
     public String getUniqueId(String tableName) {
         UUID uuid = UUID.randomUUID();
         File file = new File(dataFolder, tableName + File.separator + uuid.toString() + YML);