1. Error description

Exception in thread "main" java.lang.IllegalArgumentException: adding a window to a container
	at java.awt.Container.checkNotAWindow(Container.java:490)
	at java.awt.Container.addImpl(Container.java:1091)
	at java.awt.Container.add(Container.java:1005)
	at javax.swing.JFrame.addImpl(JFrame.java:567)
	at java.awt.Container.add(Container.java:417)
	at com.you.cmdp.frame.CheckBox.(CheckBox.java:42)
	at com.you.cmdp.frame.CheckBox.main(CheckBox.java:62)

2. The reason for the error

public CheckBox()
	{
		frame.setBounds(100, 100, 400, 300);
		frame.setFont(font);
		frame.setForeground(Color.WHITE);
		frame.setBackground(Color.BLACK);
		add(frame);
		
		cbOne.setText("Section 1");
		cbTwo.setText("Section 2");
		cbThree.setText("Section 3");
		cbFour.setText("Section 4");
		
		panel.add(cbOne);
		panel.add(cbTwo);
		panel.add(cbThree);
		panel.add(cbFour);
		
		frame.add(panel);
	}

In the constructor, JFrame is inherited, but add(frame) will not be added again

3. Solution

public CheckBox()
	{
		frame.setBounds(100, 100, 400, 300);
		frame.setFont(font);
		frame.setForeground(Color.WHITE);
		frame.setBackground(Color.BLACK);
		//add(frame);
		
		cbOne.setText("Section 1");
		cbTwo.setText("Section 2");
		cbThree.setText("Section 3");
		cbFour.setText("Section 4");
		
		panel.add(cbOne);
		panel.add(cbTwo);
		panel.add(cbThree);
		panel.add(cbFour);
		
		frame.add(panel);
	}

Read More:

• [Solved] JPA sett in parameter error: Java.lang.illegalargumentexception
• [Solved] Java.lang.ClassCastException: [Ljava.lang.Long； cannot be cast to java.util.List
• [Solved] ERROR SparkContext: Error initializing SparkContext. java.lang.IllegalArgumentException: System memo
• [Solved] Hibernate Error: java.lang.StackOverflowError at java.lang.Integer.toString(Integer.java:402）
• [Solved] nacos Startup Error: nested exception is java.lang.RuntimeException: java.lang.RuntimeException: [db-load-error
• Java uses class array to report error Exception in thread “main” java.lang.NullPointerException solution
• [Solved] Failed to convert value of type ‘java.lang.String‘ to required type ‘java.util.Date‘；
• [Solved] JAVA OpenCV Startup Error: java.lang.UnsatisfiedLinkError
• [Solved] java Internal error in the mapping processor java.lang.NullPointerException
• [Solved] java Internal error in the mapping processor java.lang.NullPointerException
• [Solved] java: Internal error in the mapping processor: java.lang.NullPointerException
• [Solved] JAVA Project Import jstl Error: java.lang.NoClassDefFoundError: javax/servlet/jsp/tagext/TagLibraryValidator
• JAVA error: java.lang.OutOfMemoryError:GC overhead limit exceeded
• [Solved] JAVA fx Error: java.lang.instrument ASSERTION FAILED ***: “!errorOutstanding“ with message transform
• [Solved] Hbase-shell 2.x Error: Unhandled Java exception: java.lang.IncompatibleClassChangeError: Found class jline.Terminal…
• [Solved] Java 9 reflection error: java.lang.reflect.InaccessibleObjectException
• [Solved] IDEA springboot Startup Error: java.lang.UnsatisfiedLinkError: no tcnative-1 in java.library.path
• java: java.lang.IllegalAccessError: class lombok.javac.apt.LombokProcessor (in unnamed module @0x590
• [Solved] Failed to start bean ‘eurekaAutoServiceRegistration‘; nested exception is java.lang.NullPointerExce
• Caused by: java.lang.IllegalStateException (How to Fix)