title: How can I know whether an instance of a class already exists in memory?
body: <p>How can I know whether an instance of a class already exists in memory?</p>
  
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  <p>My problem is that don't want read method if exist instance of Class 
  this is my code</p>
  
  <pre><code>private void jButton (java.awt.event.ActionEvent evt) {
      PNLSpcMaster pnlSpc = new PNLSpcMaster();
      jtabbedPanel.addTab("reg",pnlSpc);
  }
  </code></pre>
  
  <p>I want check instance of <code>PNLSpcMaster</code> of course I can check by static boolean but I think this way is better.</p>