Java- difference between String object and user defined objects

This is a simple java program. It contains a class "Student" and we are making its two objects stud,stud1. Similarly I have also made a String object "a" whose value is "Hello".

class Student{

  int age;

  public void setAge(int age){
    this.age=age;
  }

  public int getAge(){
    return age;
  }
}


class Hello{

  public static void main(String args[]){

    Student stud= new Student();
    Student stud1= new Student();
    stud.setAge(15);
    int i=stud.getAge();
    String a=new String("Hello");
    System.out.println(stud);
    System.out.println(stud1);
    System.out.println(a);
  }

}

As we know when we create a class object, it just holds a reference values for that object.That's why when I tried to print stud and stud1 I am getting two reference values.But since "a" is an object of class String we should expect a reference value instead of value "Hello".Why its happening?