JavaでJLabelに表示させるテキストを変更させようとしたときにエラーが発生する

解決したいこと

Java初心者です。
SwingでGUI開発をしています。ボタンのクリックイベントによって
JLabelに表示させるテキストを変更させようとしたときにエラーが発生しました。

発生している問題・エラー

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: Cannot invoke "javax.swing.JLabel.setText(String)" because "this.lblNewLabel" is null
	at testFotm.actionPerformed(testFotm.java:56)
	at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1967)
	at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2308)
	at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405)
	at java.desktop/javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262)
	at java.desktop/javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:279)
	at java.desktop/java.awt.Component.processMouseEvent(Component.java:6614)
	at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3342)
	at java.desktop/java.awt.Component.processEvent(Component.java:6379)
	at java.desktop/java.awt.Container.processEvent(Container.java:2263)
	at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:4990)
	at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2321)
	at java.desktop/java.awt.Component.dispatchEvent(Component.java:4822)
	at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4919)
	at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Container.java:4548)
	at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Container.java:4489)
	at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2307)
	at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2769)
	at java.desktop/java.awt.Component.dispatchEvent(Component.java:4822)
	at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:772)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:95)
	at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:745)
	at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:743)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
	at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:742)
	at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
	at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

該当するソースコード

java
1
2import java.awt.BorderLayout;
3import java.awt.EventQueue;
4
5import javax.swing.JFrame;
6import javax.swing.JPanel;
7import javax.swing.border.EmptyBorder;
8import javax.swing.JButton;
9import javax.swing.JLabel;
10import java.awt.Font;
11import javax.swing.SwingConstants;
12import java.awt.event.ActionListener;
13import java.awt.event.ActionEvent;
14
15public class testFotm extends JFrame implements ActionListener {
16	private JPanel contentPane;
17	private JButton btnNewButton;
18	private JLabel lblNewLabel;
19
20	/**
21	 * Launch the application.
22	 */
23	public static void main(String[] args) {
24		EventQueue.invokeLater(new Runnable() {
25			public void run() {
26				try {
27					testFotm frame = new testFotm();
28					frame.setVisible(true);
29				} catch (Exception e) {
30					e.printStackTrace();
31				}
32			}
33		});
34	}
35
36	/**
37	 * Create the frame.
38	 */
39	public testFotm() {
40		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
41		setBounds(100, 100, 450, 300);
42		contentPane = new JPanel();
43		contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
44		contentPane.setLayout(new BorderLayout(0, 0));
45		setContentPane(contentPane);
46		
47		JButton btnNewButton = new JButton("\u30AF\u30EA\u30C3\u30AF\u3057\u3066\u304F\u3060\u3055\u3044");
48		btnNewButton.addActionListener(this);
49		contentPane.add(btnNewButton, BorderLayout.SOUTH);
50		
51		JLabel lblNewLabel = new JLabel("\u30AF\u30EA\u30C3\u30AF\u3055\u308C\u305F\u3089\u6587\u5B57\u304C\u304B\u308F\u308A\u307E\u3059\uFF01");
52		lblNewLabel.setHorizontalAlignment(SwingConstants.CENTER);
53		lblNewLabel.setFont(new Font("UD デジタル 教科書体 NP-B", Font.PLAIN, 18));
54		contentPane.add(lblNewLabel, BorderLayout.CENTER);
55	}
56	public void actionPerformed(ActionEvent event) {
57		lblNewLabel.setText("クリックされました。");
58	}
59
60}
61