The magic __toString() method will be invoked automatically when the code enters the catch()statement and the custom exception message will be printed

PHP
Try catch comes under exception handeling concept where using this we control the runtime error and modify the message as we want.

// function created with exception throw
function checkdata($number){
	if($number > 10){
    	throw new Exception("Number is greater than 10");
    }
    return true;
}

// try block starts
try{
	checkdata(15);
  	echo "The number is below 10";
}
// catch block
catch(Exception $e){
	echo "Message :".$e->getMessage();
}

In above code if condition is not satisfied then it will throw exception and which gets caught by catch block and show the error message. 
Source

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