What is printed when you print an object in System.out.println() ?

Have you ever tried to print an object using System.out.println() ? 

 Most probably you must have tried printing a String or an Integer value which prints its value.

For example, let say for the following code

String s="Tom";System.out.println(s);

It will print "Tom".


or

int i=10;System.out.println(i);

will print 10.

But what will it print in following scenario.

Let say there is a class Circle with a int variable of radius.

class Circle

{

int radius;

Circle(int radius)

{

this.radius=radius;

}

}

Now let say you make an object of class Circle and print it.

Circle c= new Circle(10);

System.out.println(c);

What should I expect to get printed now? Radius of the Circle or any other thing.
When you run this code, it will print the following.

Circle@15db9742

Why this? What is that number after @ sign and why that name of class.

When any object is printed under System.out.println(), it prints its response of toString().

toString() method

java.lang.Object- Alpha class or super class for all the class that exist in Java have a method with following signature.

public String toString()

By default java.lang.Object is designed to return the following

NameofClass@Hexcode(hashCode) 

Hence the output,

Circle@15db9742

Then why is it printing it differently for String and Integer?

Simple!! They have overridden the toString() method.

Let say I want the output of Circle object when printed as "Radius=radiusValue", I will have to override the toString() method.

class Circle

{
int radius;

Circle(int radius)

{

this.radius=radius;

}
public String toString()

{

String x="Radius="+radius;

return x;

}
}

Now when you print the object of class Circle, output will be different.

Circle c=new Circle(24);

System.out.pritnln(c);

Output: Radius=24