Creating a vector

[Sam Bluesman]

Hi.

I am trying to create a vector:

Vector myVector = new Vector();

When I try an add an element to the end:

myVector.addElement(3);

and I compile I get the following message:

Note: C:\Vector.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

So, when I do that I get:

Vector.java:94: warning: [unchecked] unchecked call to addElement(E) as a member of the raw type java.util.Vector myVector.addElement(currentID);
^

What am i doing wrong? I cant seem to find any help anywhere

Thanks

[Pravin Jain]

This is a warning one gets when one uses Collection Framework classes
which have been generified in Java 5.
either you can ignore the warning or use Java 1.4 compiler.
or learn about generics and use them.

[Saket Barve]

Replacing

   
 
Vector myVector = new Vector();
 
 

with

   
 
Vector<Integer> myVector = new Vector<Integer>();
 
 

should do the trick.

[Sam Bluesman]

Thanks.

[Aby Ouseph]

3 is consider as a primitive datatype. To add 3 to that vector yo have to convert that 3 to Integer Object.
Try this before adding to vector
Integer x=new Integer(3);
then add x

[Jesper de Jong]

Also, use ArrayList instead of Vector.

Vector is a legacy collection class, from Java version 1.0. In version 1.2, new collection classes were added to Java. ArrayList is the replacement for Vector. Although the old collection classes are still in the Java API, there's no real reason anymore to use them in your programs.

See: The Collections Framework.

Originally posted by Aby Ouseph:
3 is consider as a primitive datatype. To add 3 to that vector yo have to convert that 3 to Integer Object.
Try this before adding to vector
Integer x=new Integer(3);
then add x

There's no need for that if you're using Java 5 or 6, because of autoboxing (a new feature in Java 5). This will work without errors in Java 5 or 6:

List<Integer> numbers = new ArrayList<Integer>();
 
numbers.add(3);   // The Java compiler automatically converts these ints to Integer objects
numbers.add(13);
numbers.add(22);

[ May 31, 2007: Message edited by: Jesper Young ]

[Saket Barve]

To add 3 to that vector yo have to convert that 3 to Integer Object.

Not required for JDK 1.5+ what with the Autoboxing feature.

[Kaydell Leavitt]

ArrayList is the replacement for Vector. Although the old collection classes are still in the Java API, there's no real reason anymore to use them in your programs.

I thought that Vector was still useful because it is thread-safe and that ArrayList should be used when thread-safety isn't an issue to get higher performance.

Kaydell

[Jesper de Jong]

Originally posted by Kaydell Leavitt:
I thought that Vector was still useful because it is thread-safe and that ArrayList should be used when thread-safety isn't an issue to get higher performance.

Kaydell

Thread safety is an issue only when you're writing a multi-threaded program and there are multiple threads that are modifying the same collection at the same time.

In the rare case that you really need a synchronized (thread-safe) collection, you could wrap your ArrayList in a thread-safe list like this:

List<String> data = new ArrayList<String>();
 
// Wrap the original list with a thread-safe wrapper
List<String> list = Collections.synchronizedList(data);

[Prosenjit Banerjee]

Originally posted by Saket Barve:
Replacing

Vector myVector = new Vector();

with

Vector<Integer> myVector = new Vector<Integer>();

should do the trick.

Then what if I want to add various types of objects (say, Strings, Integers, Panels) to the same vector?

[Jesper de Jong]

Originally posted by Prosenjit Banerjee:
Then what if I want to add various types of objects (say, Strings, Integers, Panels) to the same vector?

Instead of Integer use a common superclass between the objects you want to add. Since String, Integer and Panel have no other common superclass than Object, use:

Vector<Object> vector = new Vector<Object>();

Ofcourse, since Object is the superclass of all classes, this won't provide much type-safety...

Another example: Suppose you could add different kinds of numbers (integers, longs, doubles, ...). Then you could use Number as the parametric type, since Number is a common superclass of Integer, Long, Double etc.

[Kaydell Leavitt]

Vector<Object> vector = new Vector<Object>();

Is the code above the equivalent to:

Vector<?> vector = new Vector<?>();

Kaydell
[ June 21, 2007: Message edited by: Kaydell Leavitt ]