System.out.println(this)?

[Pui Shing Lee]

public class trial42 
{
static int total = 10;
 
public static void main (String args []) 
{
new trial42();
}

public trial42 () 
{
System.out.println("In test");
System.out.println(this);
int temp = this.total;
if (temp > 5) 
{
    System.out.println(temp);
}
}
}

I compile and run, the output is:
In test
trial42@107077e
10


My question is what does "System.out.println(this);" do? Why it give trial42@107077e?
[ July 25, 2005: Message edited by: Barry Gaunt ]

[Ernest Friedman-Hill]

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.

[Mohamed Shafi]

hi Pui Shing Lee,

this usually invokes the current reference object.so when u try to print using the line

System.out.println(this);

u r trying to print the object reference using toString(). check out the sample ...

class trial
{
public static void main(String args[])
{
trial obj=new trial();
System.out.println(obj);
}
}

u get output as trial@13e8d89

Hope this helps...


Regards,

Shafi.

[lalit upadheyay]

what does "System.out.println(this);" do?

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