ARRAYS - Java Programming: From Problem Analysis to Program Design - page 617

public int indexOf(Object obj, int index)
//Starting at index, the method returns the position of the
//first occurrence of the element specified by obj in the vector.
//If item is not in the vector, the method returns -1.

public boolean isEmpty()
//Returns true if the vector is empty; otherwise it returns false

public void removeAllElements()
//Removes all elements of the vector

public void removeElementAt( int index)
//If an element at position specified by index exists, it is
//removed from the vector.
//If index is out of range, this method throws an
//ArrayIndexOutOfBoundsException.

public int size()
//Returns the number of elements in the vector

public String toString()
//Returns a string representation of this vector

From Table 9-2, it follows that every element of a Vector object is a reference variable of
type Object .InJava, Object is a predefined class, and a reference variable of the Object
type can store the address of any object. Because every element of a Vector object is a
reference, to add an element to a Vector object, you must first create the appropriate object
and store the data into that object. You can then store the address of the object holding the
data into a Vector object element. Because every string in Java is considered a String
object, we will illustrate some of the operations on a Vector object using string data.
Consider the following statement:
Vector<String> stringList = new Vector<String>(); //Line 1
This statement declares stringList to be a reference variable of the Vector type, instanti-
ates an empty Vector object, and stores the address of this object into stringList .The
Vector object stringList is used to create a Vector of String objects.

9

In Java 5.0 and higher versions, whenever you declare a Vector object, you should also
specify the reference type of the objects that the Vector object will hold. To do this,
enclose the reference type of the objects between < and > after the word Vector . For
example, in the statement in Line 1, Vector<String> specifies that the Vector
object stringList is a Vector of the String object. If you do not specify the
reference type after the word Vector , the compiler will generate a warning message
indicating an unchecked or unsafe operation.