如何在Java Swing中控制JTextFields的宽度？

我已经尝试过.setColumns(),但没有任何意义.

这里是一个例子,我使用三行,三行应显示为列：

import java.awt.GridLayout;
import javax.swing.BoxLayout;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class RowTest extends JPanel {

    class Row extends JComponent {
        public Row(String str1,String str2,String str3) {
            this.setLayout(new BoxLayout(this,BoxLayout.X_AXIS));

            JTextField fld1 = new JTextField(str1);
            JTextField fld2 = new JTextField(str2);
            JTextField fld3 = new JTextField(str3);

            fld1.setColumns(5); // makes no sense

            this.add(fld1);
            this.add(fld2);
            this.add(fld3);
        }
    }

    public RowTest() {
    this.setLayout(new GridLayout(5,0));

    this.add(new Row("Short","A long text that takes up more space","Short again"));
    this.add(new Row("Longer but short","Another long string","Short"));
    this.add(new Row("Hello","The long field again","Some info"));
    }

    public static void main(String[] args) {
        new JFrame() {{ this.getContentPane().add(new RowTest());
                            this.pack(); this.setVisible(true); }};
    }

}