如何在Java中动态设置对象？

Question

I am creating an GUI application in java that uses input from the user and dynamically sets up textfield in my jFrame with default names like jTextField1,jTextField2 etc

My projects demo is as follows:-

1) It accepts number of rows and columns from combo box.

2)It should set the number of columns and rows as per the selection of user. (ie it should dynamically create Jtextfield objects on the JFrame)

Can i dynamically setup these commands inside a looping statement and create the number of textfields i need :-

     private void initComponents() {
    jTextField1 = new javax.swing.JTextField();
            jTextField2 = new javax.swing.JTextField();
}


private javax.swing.JTextField jTextField1;
    private javax.swing.JTextField jTextField2;

Or is there any other methods to do the same.

Is this Possible in any other languages like javascript or html.

Any help is appreciated !

Answer 1

Your approach is right. You loop through the indexes and create the new components (Java GUI objects) and add them to the container.

Remember to either check existing components or remove()/removeAll() them.

UPDATE: When you create a Container you usually define a LayoutManager (I am more familiar with GridBagLayout , but XYLayout could be useful for you). When adding a component to a Container, you have a method that allows an extra object constraints ; that object is passed to the layoutManager to know where / how to draw the component added.

Of course, each different layoutManager uses its own different constraints, so for the GridBagLayout I pass a GridBagConstraints object. In your example, to build a row, all the fields except the ones would be added by a default GridBagConstraints; the GridBagConstraints in the last row would have

 GridBagConstraints.gridwidth = GridBagConstraints.REMAINDER;

to notify the layout manager that it is the last item in the row.

Answer 2

You should read about Layout managers. In your case you should start from using GridLayout. Read number of rows and columns, create GridLayout with appropriate parameters. Then create text fields into the for loop (or 2 nested for loops) and add them to the panel.

You will see that the number of text fields and their positions are almost OK. Now see the problem: the text field sizes will depend on your frame size. To solve this problem you can replace your GridLayout by BoxLayout or GridBagLayout or use nested panel with flow layout or use third party tool like MigLayout .

Answer 3

First of all: You can use arrays for your text fields:

JTextField[][] matrix1TextFields, matrix2TextFields, matrix3TextFields;
private void refreshMatrixComponents(int r, int c) {
  matrix1TextFields = new JTextField[r][c];
  matrix2TextFields = new JTextField[r][c];
  matrix3TextFields = new JTextField[r][c];
  for (int row = 0; row < r; row++) {
    for (int col = 0; col < c; col++) {
      matrix1TextFields[row][col] = new JTextField();
      matrix2TextFields[row][col] = new JTextField();
      matrix3TextFields[row][col] = new JTextField();
    }
  }
  placeMatrixTextField();  
}

For the layout manager, there are a lot of options. I would either recommend GridLayout (very easy to use) or GridBagLayout (more difficult to use, but more flexible) or something 3rd party like MigLayout (you will have to dive into the syntax a bit, but I think it's totally worth the effort). I also recommend creating a JPanel for every matrix and put all the text fields in there. Then place those JPanels + the rest of the components:

JPanel matrix1Panel, matrix2Panel, matrix3Panel;
private void placeMatrixTextField() {
  int r = matrix1TextFields.length, c = matrixTextFields[0].length;
  matrix1Panel = new JPanel();
  matrix2Panel = new JPanel();
  matrix3Panel = new JPanel();
  matrix1Panel.setLayout(new GridLayout(r, c));
  matrix2Panel.setLayout(new GridLayout(r, c));
  matrix3Panel.setLayout(new GridLayout(r, c));
  for (int row = 0; row < r; row++) {
    for (int col = 0; col < c; col++) {
      matrix1Panel.add(matrix1TextFields[row][col]);
      matrix2Panel.add(matrix2TextFields[row][col]);
      matrix3Panel.add(matrix3TextFields[row][col]);
    }
  }
  // now place your panels
}