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Editorial Team
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Asked: 2026-06-17T14:57:46+00:00

I am implementing a program for a Component Design course and am currently struggling

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I am implementing a program for a Component Design course and am currently struggling with what should be simple use of a Jlist. The program draws shapes and should display them in a JList in a ScrollPane in the BorderLayout.West of the frame.

The current program shows the ScrollPane but will not display objects I add to the shapeListModel like it should. I am wondering it I am missing something or if something is flat out wrong with my code. Currently this is all the code that partains to the JList creation, assigning, and updating.

    //Class Variable Declaration
protected ArrayList<Shape> shapes = new ArrayList<Shape>();
private JScrollPane shapeScrollPane = new JScrollPane();
private JList<String> shapeList;
protected DefaultListModel<String> shapeListModel;

    //Creation of JList objects and what not
shapeListModel = new DefaultListModel<String>();

    //This element is added aimply to try and get one to show up on my JList, 
shapeListModel.addElement("SERIOUSLY FRUSTRATED"); 
    //It does not just so you know

shapeList = new JList<String>(shapeListModel);
shapeList.setModel(shapeListModel);

    //Adding JList to ScrollPane and setting size
shapeScrollPane.add(shapeList);
shapeScrollPane.setPreferredSize(new Dimension(250,600));

//Clarifying JList actions  
shapeList.setSelectionMode(ListSelectionModel.SINGLE_INTERVAL_SELECTION);
shapeList.setLayoutOrientation(JList.HORIZONTAL_WRAP);
shapeList.setVisibleRowCount(-1);
shapeList.addListSelectionListener(this);**

    //This is called everytime a new shape is created and adds it to the Arraylist
    //shapes and the DefaultListModel shapeListModel
shapes.add(newShape);
shapeListModel.addElement(newShape.toString());

I apologize for my poorly formatted question a few moments ago. I have been stuck on this for approximately 4 hours, the last two hours spent searching for answers online. I am now resulting to asking anyone if they see an issue within the code I have.

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1 Answer

  1. Editorial Team

    You don’t “add” components a scroll pane. You need to set it’s view ports view instead.

    Don’t do this…

    shapeScrollPane.add(shapeList);

    Do this…

    shapeScrollPane.setViewportView(shapeList);

    Check out

    Also, this shapeList.setVisibleRowCount(-1) scares me to no end.

    Updated

    You also don’t need to this…

    shapeList = new JList<String>(shapeListModel);
shapeList.setModel(shapeListModel);

    This is more then sufficient…

    shapeList = new JList<String>(shapeListModel);

    Updated

    Also, if this is the same code that was used in a previously closed question…

    This canvas.getGraphics() terrifies me!! If your instructor gave you this code, then they shouldn’t be teaching you!

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