如何在构造函数外添加Jlabel到Jpanel？

Question

我可以使用add(new Jlabel())在Jpanel构造函数中的Jpanel上创建标签,但是一旦我使用其他函数调用add(),标签就不会显示在面板上.我做错了什么？

public class DisplayPanel extends JPanel {


        JLabel headerField = new JLabel("Choose a file to generate report.");

        JLabel dateField = new JLabel("123");
        JLabel meanField = new JLabel("");

        JLabel minField = new JLabel("");

        JLabel maxField = new JLabel("");

        JLabel stdDevField = new JLabel("");

        public DisplayPanel() {
        super();
                setBackground(Color.white);
                setLayout(new GridLayout(6, 1));


        add(headerField);
        **//add(new JLabel("123")); this will work**

        }


        public void setFields(DataManager d)
        {
            dateField.setText(d.getStartDate() + " - " + d.getEndDate());
            meanField.setText("Mean: " + d.getMean());
            minField.setText("Min: " + d.getMin());
            maxField.setText("Max: " + d.getMax());
            stdDevField.setText("Std Dev: " + d.getStdev());
            this.add(new JLabel("123")); **//this doesn't work**
        }

Answer 1

为了使任何新添加的组件JPanel在可见之后显示,您需要调用revalidate()并且通常repaint().原因

add(new JLabel("123"));

在构造函数中工作,JPanel在添加到其容器时验证,通常是a JFrame.在inialization阶段添加标签更简单,因为您只需要调用JLabel#setText并且不需要revalidate/repaint调用.