How to get a specific type object from an Object Vector in Java

Question

I have the following Vector and at runtime I want to pass it an Integer, Character, or Float:

public static Vector<Object> interestingValues = new Vector<Object>();

At the same time I want to get an Integer, Float, or Character from it, so there are two things:

• Will they retain the specific Integer/Float/Character type in the Object Vector, or they all will be stored in the form of Object?

• How can I retrieve Integer objects from this Vector?

Answer 1

Casting:

Integer i=(Integer)interestingValues.get(0);

In case you have multiple types of objects inside the Vector you could check the type using instanceof:

Object o=interestingValues.get(0);
 if (o instanceof Integer){
      Integer i=(Integer)o;
 }else if (o instanceof Long){
      Long l=(Long)o;
 }

The third thing you can do to avoid the need ov casting objects to a particular type is using a typed Vector:

Vector <Integer> integerVector=new Vector<Integer>();
integerVector.add(Integer.MAX_VALUE);
Integer i=integerVector.get(0);

Answer 2

Try using the instanceof and casting :

if(interestingValues.get(0) instanceof Integer){
Integer value = (Integer) interestingValues.get(0);
}

Answer 3

The Vector only stores a reference to the object, not the object itself.

However since the (non generic) class is defined as storing references to Object you have to cast the stored references back to the original type before using them:

String s = (String)myVector.get(n);

That does of course require that you know in advance which particular type is stored in which element...

You could do:

Object o = myVector.get(n);
if (o instance String) {
    // do string stuff
} else if (o instanceof Integer) {
    // do integer stuff
} etc 

Answer 4

You'll have to iterate and check for Integer instances, for example:

List<Integer> integers = new ArrayList<Integer>();
for (Object object:interestingValues) {
  if (object instanceof Integer)
     integers.add((Integer) object);
}

Answer 5

You'd have to check the class of the object:

Object obj = myvector.get(0);
if( obj instanceof Integer) {
 Integer myInt = (Integer)obj;  
}
else if( obj instanceof Character ) {
  Integer myChar = (Character)obj; 
}

That's not a good design though. You might want to consider storing the objects in different vectors or using a comming representation (e.g. String) along with conversion.

Edit:

Since Float, Integer and the like all extend Number you might also just check for obj instanceof Number and then call intValue(), doubleValue() etc. on the casted object if all you need is the number and not the type.

Answer 6

instanceof checks the "isa" releationship. If you want to be 100% sure of the class, use getClass(). here is a long winded example:

public class Blue
{
  private String yargh;

  public Blue()
  {
    yargh = "blue";
  }

  public Blue(final String value)
  {
    yargh = StringUtils.defaultString(value);
  }

  public void println()
  {
    System.out.println(yargh);
  }
}

public class Berry extends Blue
{
  public Berry()
  {
    super("blueberry");
  }
}

... blah blah blah
Vector<Object> stuff = new ... blah blah blah
stuff.add(new blue());
stuff.add(new berry());

Iterator<Object&gt iterator = stuff.iterator();
Object minemine;

// this calls println on two objects.
while (iterator.hasNext())
{
  minemine = iterator.next();
  if (minemine instanceof Blue)
  {
    Blue bluemine = (Blue)minemine;
    bluemine.println();
  }
}

// This calls println for the Blue object, but not the Berry object.
iterator = stuff.iterator();
while (iterator.hasNext())
{
  minemine = iterator.next();
  if (minemine.getClass() == Blue.class)
  {
    Blue bluemine= (Berry)minemine;
    bluemine.println();
  }
}

Caveat emptor: I did not complile the code above.