How to check if jQuery is already loaded

// code to check if jquery is loaded already
/*
 * ------------------------------------------------------
 * First Method
 * ------------------------------------------------------
 */
try{
  var jQueryIsLoaded=jQuery;
  jQueryIsLoaded=true;
}
catch(err){
  var jQueryIsLoaded=false;
}

if(jQueryIsLoaded){
  // jQuery is loaded
}
else{
  // jQuery NOT loaded
}

/*
 * ------------------------------------------------------
 * Second Method
 * ------------------------------------------------------
 */
if (typeof jQuery == 'undefined') 
{  
    //it's not loaded so load it here
} else 
{
    //already loaded, do something here
}