Introduction to Vectors in java

Vectors (the java.util.Vector class) are commonly used instead of arrays, because they expand automatically when new data is added to them. The Java 2 Collections API introduced the similar ArrayList data structure. ArrayLists are unsynchronized and therefore faster than Vectors, but less secure in a multithreaded environment. The Vector class was changed in Java 2 to add the additional methods supported by ArrayList. See below for a reasons to use each. The description below is for the (new) Vector class.
Vectors can hold only Objects and not primitive types (eg, int). If you want to put a primitive type in a Vector, 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.