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我想通過FlowLayout向JFrame添加一個JPanel，但繼續得到這個異常：「線程中的異常」AWT-EventQueue-0「java.lang.IllegalArgumentException：非法組件位置」。我希望在不久的將來能夠實現帶有幾個按鈕的JPanel，所以請讓我知道我可以做些什麼來允許這樣做。我正在嘗試使用Flowlayout將Janel添加到JFrame中，但繼續發生異常。我做錯了什麼？
package textadv;
import java.awt.FlowLayout;
import java.awt.Button;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Label;
import java.awt.event.KeyEvent;
import javax.swing.AbstractButton;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class TextAdv {
private JFrame frame = new JFrame("Text Adventure");
private JPanel mainPanel = new JPanel(new FlowLayout(FlowLayout.LEFT));
private JButton b1 = new JButton("Left");
public TextAdv() {
mainPanel.setBackground(Color.RED);
int FRAME_WIDTH = 400;
int FRAME_HEIGHT = 400;
b1.setEnabled(true);
b1.setVisible(true);
b1.setPreferredSize(new Dimension(40, 40));
mainPanel.setVisible(true);
mainPanel.setPreferredSize(new Dimension (50, 50));
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
frame.setVisible(true);
mainPanel.add(b1, FlowLayout.CENTER);
frame.add(mainPanel);
}
public static void main(String[] args) {
java.awt.EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
TextAdv fS = new TextAdv();
}
});
}