println(Object) calls toString() on the argument; this String is then displayed. See the Javadocs for java.lang.Object.toString() (which your class inherits, because it doesn't override this method) for a detailed explanation.
It implicitly invokes the toString() method for anything supplied to it as parameter ( whether primitive or object references ), here the current object reference . Since your class does not provide implementation of public String toString(Object o) method , it will inherit implemenattion from its parent class i.e. Object class, and will invoke it here.
Why it give trial42@107077e? If your class does not override the implementation of toString() method inherited by your class from the Object class ( grand dady of all classes ) then you will get class name here trial42 followed by hashCode() for the object. For details regarding these methods i would suggest you to refer to API documentation for Object class