class TestFrame extends JFrame {
private JPanel buttonPanel; private static int FRAME_WIDTH = 350;
private static int FRAME_HEIGHT = 500;
/**
*
*/
private static final long serialVersionUID = 1L; public TestFrame() {
setTitle("First Swing Test");
setSize(FRAME_WIDTH, FRAME_HEIGHT); /**
* 你写了一个 buttonPanel 变量,但是却没有给它赋值,所以出现了空指针的问题。 下面我给它进行了赋值,问题就解决了。
*/
buttonPanel = new JPanel();
add(buttonPanel);
makeButton("yellow", Color.YELLOW);
makeButton("pink", Color.PINK);
makeButton("red", Color.RED); } public void makeButton(String name, final Color backgroundColor) {
JButton button = new JButton(name);
buttonPanel.add(button); button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
buttonPanel.setBackground(backgroundColor);
}
});
}}
private JPanel buttonPanel; private static int FRAME_WIDTH = 350;
private static int FRAME_HEIGHT = 500;
/**
*
*/
private static final long serialVersionUID = 1L; public TestFrame() {
setTitle("First Swing Test");
setSize(FRAME_WIDTH, FRAME_HEIGHT); /**
* 你写了一个 buttonPanel 变量,但是却没有给它赋值,所以出现了空指针的问题。 下面我给它进行了赋值,问题就解决了。
*/
buttonPanel = new JPanel();
add(buttonPanel);
makeButton("yellow", Color.YELLOW);
makeButton("pink", Color.PINK);
makeButton("red", Color.RED); } public void makeButton(String name, final Color backgroundColor) {
JButton button = new JButton(name);
buttonPanel.add(button); button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
buttonPanel.setBackground(backgroundColor);
}
});
}}
解决方案 »
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