Java SE (Java Platform, Standard Edition)

I have this code:

  public String readInputFile(String text) {
    JOptionPane.showMessageDialog(new JFrame(), text);
    // add stuff later here...
    return text;
  }

But when I run it from eclipse it never terminates (the red button never goes gray). But if I do:

  public String readInputFile(String text) {
    JFrame jFrame = new JFrame();
    JOptionPane.showMessageDialog(jFrame, text);
    // add stuff later here...
    jFrame.dispose();
    return text;
  }

it terminates nicely. But is it necessary to declare the JFrame as a local variable and call dispose to make this work?