some lines compile some don't

below are snipets of my code. As you see I note that some lines compile some don't. what is wrong with the snippets that don't ? thanks



JMenuBar menuBar;//compiles must be right
 menuBar = new JMenuBar();// compiles must be right

JMenu menu = new JMenu("Menu Label");// compiles must be right
    menuBar.add(menu);// compiles must be right

 JMenuItem item = new JMenuItem("Item Label");// compiles must be right

 //frame.setJMenuBar(menuBar);//doesn't compile, what is wrong?  
//item.addActionListener(actionListener);//doesn't compile, what is wrong?

 menu.add(item); // compiles must be right

 // frame.setJMenuBar(menuBar);//doesn't compile, what is wrong?