What is the use of printStackTrace() method in Jav

Question

I am going through a socket program. In it, printStackTrace is called on the IOException object in the catch block.
What does printStackTrace() actually do?

catch(IOException ioe)
{
    ioe.printStackTrace();
}

I am unaware of its purpose. What is it used for?

Answer 1

It's a method on Exception instances that prints the stack trace of the instance to System.err.

It's a very simple, but very useful tool for diagnosing an exceptions. It tells you what happened and where in the code this happened.

Here's an example of how it might be used in practice:

try {
    // ...
} catch (SomeException e) { 
    e.printStackTrace();
}

Answer 2

I was kind of curious about this too, so I just put together a little sample code where you can see what it is doing:

try {
    throw new NullPointerException();
}
catch (NullPointerException e) {
    System.out.println(e);
}

try {
    throw new IOException();
}
catch (IOException e) {
    e.printStackTrace();
}
System.exit(0);

Calling println(e):

java.lang.NullPointerException

Calling e.printStackTrace():

java.io.IOException
      at package.Test.main(Test.java:74)

Answer 3

printStackTrace is a method of the Throwable class. This method displays error message in the console; where we are getting the exception in the source code. These methods can be used with catch block and they describe:

1. Name of the exception.
2. Description of the exception.
3. Location of the exception in the source code.

The three methods which describe the exception on the console (in which printStackTrace is one of them) are:

1. printStackTrace()
2. toString()
3. getMessage()

Example:

public class BabluGope {
    public static void main(String[] args) {
        try {
            System.out.println(10/0);
         } catch (ArithmeticException e) {
             e.printStackTrace();   
             // System.err.println(e.toString());
             //System.err.println(e.getMessage());  
         }
    }
}