By default, when the close button on a frame is clicked, the frame hides itself. This example shows how to exit the application when the frame is closed: 
    // Create a frame
    JFrame frame = new JFrame();
    
    // Get default close operation
    int op = frame.getDefaultCloseOperation(); // HIDE_ON_CLOSE
    
    // Set to exit on close
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

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