After __toString() no code is working in php - php

Question

In following code after __toString() the php code is not working why ?
class Student{
private $name;
private $roll_no;
function __construct($name,$roll_no){
$this->name = $name;
$this->roll_no = $roll_no;
}
public function display(){
echo "Name :".$this->name;
echo "<br> Roll No :".$this->roll_no."<br><br>";
}
function __toString(){
$this->display();
}
}
$std1 = new Student("Bob" , 1);
echo $std1;
$std2 = new Student("John" , 2);
echo $std2;
$std3 = new Student("Tony" , 3);
echo $std3;
$std4 = new Student("Teena" , 4);
echo $std4;
The out put in browser is bellow : Name :Bob
Roll No :1 Rest of the lines are not working;

Answer 1

Try this
class Student{
private $name;
private $roll_no;
function __construct($name,$roll_no){
$this->name = $name;
$this->roll_no = $roll_no;
}
public function display(){
return "Name :".$this->name."<br> Roll No :".$this->roll_no."<br><br>";
}
function __toString(){
return $this->display();
}
}
$std1 = new Student("Bob" , 1);
echo $std1;
$std2 = new Student("John" , 2);
echo $std2;
$std3 = new Student("Tony" , 3);
echo $std3;
$std4 = new Student("Teena" , 4);
echo $std4;

Answer 2

Method __toString should return String not call output function. In Your code you done something like echo echo, because inside method display echo is called again. Change __toString to:
return $this->display();
and display method to:
return "Name :".$this->name."<br> Roll No :".$this->roll_no."<br><br>";
This solution fixes Your errors, but You should change display method name to something more matching its current behavior like getString().
Looking at naming conversion ( display method name ) most logical would be such approach:
class Student{
private $name;
private $roll_no;
function __construct($name,$roll_no){
$this->name = $name;
$this->roll_no = $roll_no;
}
public function display(){
echo $this; //conversion to string and echo
}
function __toString(){
return "Name :".$this->name."<br> Roll No :".$this->roll_no."<br><br>";
}
}
So I use inside display method conversion to String by __toString. Current usage would be:
$std1=new Student("Bob" , 1);
$std1.display();
//or the same:
echo $std1; //the same thing like $std1.display();