放置JscrollBar后未显示swing Java JTextArea

Question

我是Jframes的新手，我想设计一个带有文本框和两个按钮的窗口。除了滚动条部分，我可以让它工作。 我已经编写了下面的代码来启用文本区域的滚动条

private JTextArea outputPane;
outputPane = new JTextArea();
outputPane.setColumns(20);
outputPane.setRows(5);
outputPane.setFont(new Font("Monospaced", Font.PLAIN, 18));
outputPane.setBounds(12, 13, 408, 189);
contentPane.add(outputPane);

JScrollPane scrollPane = new JScrollPane(outputPane);
jScrollPane1.setBounds(399, 13, 21, 189);
scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);

现在的问题是，我在窗口上得到一个禁用的滚动条，但我看不到我的文本区域

请帮我解决这个问题。我甚至尝试过使用WindowsBuilder，但我想不出来

详细的解释与更正的代码将不胜感激，因为我仍然在学习阶段

提前谢谢

Answer 1

首先看一下Laying Out Components Within a Container和How to Use Scroll Panes和How to Use Text Areas可能不会有什么害处

Now the problem is I am getting a disabled scrollbar on the window but I cannot see my Text Area.

可能的问题是，您看到的是JTextArea，“禁用”滚动条只是因为您使用的是scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS，它将始终显示滚动条，即使没有什么可滚动的，所以它可能看起来是空的

import java.awt.BorderLayout;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        // Swing is not thread safe, so need to get started in the
        // Event Dispatching Thread before we do anything
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    // I simply hate the default look and feel                      
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                // Always better to create an instance of a window
                // to display you content then to extend from one  
                // directly...
                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    // Our main UI, I do it this way so I'm not locked into a single
    // use case and can decide how I want to use the view
    public class TestPane extends JPanel {

        public TestPane() {
            // The default layout is a FlowLayout, so we want to change
            // this will allow the main component to occupy the whole
            // available space
            setLayout(new BorderLayout());
            // Providing "sizing" hints, 10 rows, 20 columns, this is
            // platform independent, so it will size accordingly
            JTextArea ta = new JTextArea(10, 20);
            JScrollPane sp = new JScrollPane(ta);
            add(sp);
        }

    }

}