IllegalArgumentException when adding components to JFrame

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IllegalArgumentException when adding components to JFrame

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#1 by (3 votes)

2

I'm doing a Sokoban game project, and got to the point where I created 2 JButtons to select the level. Now when I try to run a program a mistake. I created both the buttons and the action in a class Buttons and called it this class in another class that gives start to the program. I used the following for the buttons:

public class Buttons extends JFrame implements ActionListener {
    private static final long serialVersionUID = 1L;

    public Buttons(){
        this.getContentPane().setLayout(new FlowLayout());
        JButton lvl1btn = new JButton("Level 1");
        JButton lvl2btn = new JButton("Level 2");
        lvl1btn.setBounds(700,0,100,25);
        lvl1btn.setBounds(800,0,100,25);
        lvl1btn.addActionListener(this);
        lvl2btn.addActionListener(this);
        lvl1btn.setActionCommand("Level 1");
        lvl2btn.setActionCommand("Level 2");
    }


    @Override
    public void actionPerformed(ActionEvent e) {
        String action = e.getActionCommand();
        if(action.equals("Level 1")){
            Board board = new Board();
            board.createWorldOne();
        }else if(action.equals("Level 2")){
            Board board = new Board();
            board.createWorldTwo();
        }
    }

And I called it:

public final class SokobanStart extends JFrame {

public SokobanStart() {
    InitUI();
}

public void InitUI() {
    Board board = new Board();
    Buttons buttons = new Buttons();
    add(board,buttons);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(board.getBoardWidth(),board.getBoardHeight());
    setLocationRelativeTo(null);
    setTitle("Sokoban Game!");
}


public static void main(String[] args) {
    SokobanStart sokobanStart = new SokobanStart();
    sokobanStart.setVisible(true);
}

}

And get the following thread:

Exception in thread "main" java.lang.IllegalArgumentException: can not add to layout: constraint must be a string (or null) at java.desktop / java.awt.BorderLayout.addLayoutComponent (BorderLayout.java:431) at java.desktop / javax.swing.JRootPane $ 1.addLayoutComponent (JRootPane.java:507) at java.desktop / java.awt.Container.addImpl (Container.java:1148) at java.desktop / java.awt.Container.add (Container.java:1025) at java.desktop / javax.swing.JFrame.addImpl (JFrame.java:553) at java.desktop / java.awt.Container.add (Container.java:993) at Sokoban.SokobanStart.InitUI (SokobanStart.java:16) at Sokoban.SokobanStart. (SokobanStart.java:10) at Sokoban.SokobanStart.main (SokobanStart.java:25)

java swing jbutton

asked by anonymous 24.06.2018 / 14:02

1 answer

Ignore reading the first input VBA Migration to C # - V10 (CustomerID)

score 3 · Accepted Answer

This line here is the cause of the error:

add(board,buttons);

You have not put a complete code, so I'm guessing that this Board class is some other component that you've created.

If you look in the class documentation JFrame , you'll see that none of the add methods that it inherits receive 2 components at the same time, that row is wrong. If you want to add board and buttons to JFrame , it needs to be one at a time, you need to break this add:

add(board);
add(buttons);

Only this would still still be an error because the Buttons class is a JFrame and you can not add a JFrame to another. You will have to transform these Buttons and Board classes into JPanel if you want to add them this way.

Note the recommendation below:

Avoid using absolute layout unless you are in dire need and know the consequences , because absolute layout makes it difficult to maintain the screen and make your application look different depending on the monitor and resolution being executed.

There are several layouts managers for you to you do not have to worry about manual positioning or organization of components. Not to mention that the use of layouts makes your code easier to maintain than inserting a lot of setbounds , and in case you need to change the position of any component, in the absolute layout, you will have to reposition them all manually.

And it's also worth noting that all graphical applications involving the swing API should be dispatched to EDT .

I recommend to study: Creating a GUI With JFC / Swing