Calling methods without an object

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Java

Hello everyone!

I'm new to java and java swing.

I'm learning java language and swing at the same time.

I have some code with JFrame like this:

import javax.swing.JFrame;
import javax.swing.JLabel;

public class mainFrame extends JFrame {
	private JLabel lb1;
	public mainFrame()
	{
		super("Title");
		setVisible(true);
		setSize(200, 150);	
		lb1 = new JLabel();
		lb1.setText("Hello world!");
		add(lb1);
	}
	public static void main(String args[])
	{
		mainFrame frm1 = new mainFrame();
	
	}	
}

The point is:
1. what is the meaning of using super(). Is that true if super() is used only in constructors?
2. Calling method setVisible(true) or setSize(200, 150) and add(lb1) without an instance (object) sounds very strange to me? I thought I must have been like someObject.setVisible()???

I think my explanation is clear enough!

Any help or suggesstion would be greatly appreciated!