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The correct answer to the quiz is the program output shown below:
Collection contents
B0 B1 L2 B3 B4 L5New array contents
B0 B1 L2 B3 B4 L5Modified array contents
XX B1 L2 B3 B4 L5Collection contents
XX B1 L2 B3 B4 L5 If that was your answer, you probably already understand most of the material covered in this module. In that case, you might consider skipping this moduleand moving on to the next module. If that wasn't your answer, you should probably continue with your study of this module.
The code in Listing 2 creates and populates a new LinkedList object and saves the object's reference as the interface type Collection . The collection is populated by passing the LinkedList object's reference to a method named fillIt .
The code in Listing 2 also displays the contents of the LinkedList after it has been populated. The list is displayed by passing the LinkedList object's reference to a method named showCollection .
| Listing 2 . A new LinkedList collection. |
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Collection ref;
ref = new LinkedList();Populator.fillIt(ref);
System.out.println("Collection contents");showCollection(ref); |
The LinkedList class is one of the concrete class implementations of the Collections Framework . This class implements the Collection interface and the List interface. Thus, it adheres to the contracts and stipulations of the List interface.
Here is part of what Oracle has to say about this class:
"Linked list implementation of the List interface. Implements all optional list operations, and permits all elements (including null). Inaddition ..."
The beginning of the static fillIt method, used to populate the collection, is shown in Listing 3 .
| Listing 3 . Beginning of the fillIt method. |
|---|
public static void fillIt(Collection ref){
ref.add(new JButton());ref.add(new JButton());
ref.add(new JLabel());ref.add(new JButton());
ref.add(new JButton());ref.add(new JLabel()); |
As shown in Listing 3 , the fillIt method begins by calling the add method six times in succession, passing references to new anonymous objects as aparameter to the add method.
Four of the objects are instantiated from the class named JButton . Two of the objects are instantiated from the class named JLabel .
Both JButton and JLabel belong to the javax.swing package. Further, both are subclasses of the class named JComponent .
Finally, both classes have a property named toolTipText , which can be set and accessed by calling the following methods on a reference to the object:
void setToolTipText(String text)String getToolTipText() I really don't plan to do anything special with these Swing GUI components. Rather, I chose to use them for illustration purposes simply becausethey possess the characteristics that I need for this module, and the nextmodule as well. Those characteristics are:
Notification Switch
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