Swing - how to mix JTextField and JTextAreas and have same visual appearance?

I know this question is pretty old, but to get the border for a TextArea to match that of a TextField:

(myTextArea).setBorder(new TextField().getBorder());

That should give a border to your TextArea like the one around a TextField.

Not sure how you can fix your border problem but to fix your layout situation I would just use springlayout. Springlayout is just a way to better layout your elements within the JPanel. You can find out more about it Java Sun Tutorial

Specifically you use it by setting where you want your North, South, West and East borders of each element. To do this you would have to first take your label calls out of the add so each one can be named. So instead of:

add(new JLabel("Text field:"));

Do:

JLabel myLabelName = new JLabel("Text field:");
add(myLabelName);

For each of your elements (JLabels, JTextAreas and JTextField). Once this is done you can easily set the layout.

Springlayout layout = new SpringLayout();
setLayout(layout);

Then for each of the elements you have to set any of the borders you want. They have to be in the specific order South, the North, West then East. Though you don't have to use all four borders if you don't want to. Here is an example on how to set your first text area, the one on the top.

layout.putConstraint(SpringLayout.NORTH, FirstTextAreaName, 10, SpringLayout.NORTH, this);
layout.putConstraint(SpringLayout.WEST, FirstTextAreaName, this.getWidth()/2, SpringLayout.WEST, this);
layout.putConstraint(SpringLayout.EAST, FirstTextAreaName, -10, SpringLayout.EAST, this);

This example doesn't set the south of the text area but if you did want to it would have to be first. The first line sets the north side of the text area to be 10 pixels away from the top. When setting the other areas you but the previous (above) areas name instead of this and say it is 10 pixels away from the south of the previous one:

layout.putConstraint(SpringLayout.NORTH, SecondTextAreaName, 10, SpringLayout.SOUTH, FirstTextAreaName);

The second line in the above example sets the east side of the text area to start halfway through your main panel. The last, third, line sets the east side of the text area to be 10 pixels from the east side of your main panel.

For the layout problem, try a columnConstraints value of [right][fill] instead of [right][left].

For the other issue, this appears to be a look-and-feel inconsistency. I ran your code in Windows, and the differences are there too, but less flagrant. My suggestion would be to set identifical borders explicitly for text fields and text areas.

setLayout(new MigLayout(
        "wrap 2",
        "[right][fill]"
        ));

JTextField textField;
JScrollPane scrollPane;

add(new JLabel("Text field:"));
textField = new JTextField(NUM_CHARACTERS_WIDTH);
textField.setBorder( new EtchedBorder( EtchedBorder.LOWERED ) );
add(textField);

add(new JLabel("No scrollpane text area:"));
add(new JTextArea(NUM_ROWS, NUM_CHARACTERS_WIDTH));

add(new JLabel("Scrollpane text area:"));
scrollPane = new JScrollPane(new JTextArea(NUM_ROWS, NUM_CHARACTERS_WIDTH));
scrollPane.setBorder( new EtchedBorder( EtchedBorder.LOWERED ) );
add(scrollPane);

add(new JLabel("Text field:"));
textField = new JTextField(NUM_CHARACTERS_WIDTH);
textField.setBorder( new EtchedBorder( EtchedBorder.LOWERED ) );
add(textField);

If you can't get MigLayout to align your components, considering using java.awt.GridBagLayout:

import static java.awt.GridBagConstraints.*;

setLayout( new GridBagLayout() );

GridBagConstraints leftCons = new GridBagConstraints();
leftCons.anchor = NORTHEAST;
leftCons.fill = NONE;
leftCons.weightx = 1.0;
leftCons.gridy = RELATIVE;
leftCons.gridx = 0;
leftCons.insets = new Insets( 4, 8, 4, 8 );

GridBagConstraints rightCons = new GridBagConstraints();
rightCons.anchor = NORTHWEST;
rightCons.fill = HORIZONTAL;
rightCons.weightx = 1.0;
rightCons.gridy = RELATIVE;
rightCons.gridx = 1;
rightCons.insets = leftCons.insets;

add(new JLabel("Text field:"), leftCons);
add(new JTextField(NUM_CHARACTERS_WIDTH), rightCons);

add(new JLabel("No scrollpane text area:"), leftCons);
add(new JTextArea(NUM_ROWS, NUM_CHARACTERS_WIDTH), rightCons);

add(new JLabel("Scrollpane text area:"), leftCons);
add(new JScrollPane(new JTextArea(NUM_ROWS, NUM_CHARACTERS_WIDTH)), rightCons);

add(new JLabel("Text field:"), leftCons);
add(new JTextField(NUM_CHARACTERS_WIDTH), rightCons);