core/src/main/java/com/orientechnologies/orient/core/db/OrientDB.java
public boolean createIfNotExists(String database, ODatabaseType type, OrientDBConfig config) {
    if (!this.internal.exists(database, serverUser, serverPassword)) {
      this.internal.create(database, serverUser, serverPassword, type, config);
      return true;
    }
    return false;
  }
public boolean createIfNotExists(String database, ODatabaseType type, OrientDBConfig config) {
    if (!this.internal.exists(database, serverUser, serverPassword)) {
      this.internal.create(database, serverUser, serverPassword, type, config);
      return true;
    }
    return false;
  }
Create a new database if not exists

@param database database name
@param type     can be plocal or memory
@param config   custom configuration for current database

@return true if the database has been created, false if already exists