Use ArrayList when there will be a large variation in the amount of data that you would put into an array.

A disadvantage of a ArrayList is that it holds only Objects and not primitive types (eg, int). To use a primitive type in an ArrayList, put it inside an object (eg, to save an integer value use the Integer class or define your own class). If you use the Integer wrapper, you will not be able to change the integer value, so it is sometimes useful to define your own class.

Java Metadata is the Interface standard for metadata management. Most JDBC programs are designed to work with a specific database and particular tables in that database; the program knows exactly what kind of data it is dealing with.

Some applications, however, need to dynamically discover information about result set structures or underlying database configurations.

This information is called metadata, and JDBC provides two classes for dealing with it: DatabaseMetaData and ResultSetMetaData.