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After the code in Listing 3 has been executed, the buttons and labels are indistinguishable on the basis of the null value of their toolTipText property.
The code in Listing 4 deals with this issue. This code uses the setToolTipText method to store a unique String value in the toolTipText property of the object referred to by each of the elements in the collection.
| Listing 4 . Making the objects distinguishable. |
|---|
Iterator iter = ref.iterator();
int cnt = 0;JComponent refVar;
while(iter.hasNext()){refVar = (JComponent)iter.next();
if(refVar instanceof JButton){refVar.setToolTipText("B"+cnt++);
}else{refVar.setToolTipText("L" + cnt++);
}//end else}//end while loop
}//end fillIt() |
In addition to storing a unique value in the toolTipText property of the object referred to by each element, the code in Listing 4 also makes it possible to distinguish between the JButton objects and the JLabel objects. This is accomplished by including an upper-case "B" in the propertyvalue for each JButton , and including an upper-case "L" in the property value for each JLabel button.
This approach to population is, admittedly, a little bit of an overkill for illustrating what I want to illustrate in this program. However, I plan to usethe same fillIt method in the sample program in the next module, and it won't be an overkill there.
The code in Listing 2 above calls the showCollection method to display the contents of the populated LinkedList collection. The showCollection method is shown in Listing 5
| Listing 5 . The showCollection method. |
|---|
void showCollection(Collection ref){
Iterator iter = ref.iterator();while(iter.hasNext()){
System.out.print(((JComponent)iter.next()).getToolTipText() + " ");
}//end while loopSystem.out.println();
}//end showCollection |
By now, you should have no difficulty understanding the code in Listing 5 . This code gets an iterator on the incoming reference of type Collection . The code then uses that iterator to gain access to each element in succession,displaying the String value of the toolTipText property belonging to a particular object during each iteration.
Note that the next method of the Iterator interface returns a reference to the next element in the collection, as type Object . (Remember, Generics were not used to populate this collection.)
In order to call the getToolTipText method on the returned reference, the reference must be downcast to type JComponent . Since both JButton and JLabel extend JComponent , and the getToolTipText method is declared in the JComponent class, it is not necessary to be concerned as to whether an object is type JButton or type JLabel to display the value of the toolTipText property. (This is an example of polymorphic behavior based on class inheritance.)
The output produced by the code in Listing 2 is shown below:
Collection contentsB0 B1 L2 B3 B4 L5 By examining the "B" and "L" characters in this output, you can identify the JButton objects and the JLabel objects.
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