Return or Print StringBuilder? Java -

i bit confused stringbuilder. seems when print stringbuilder, there no need add .tostring() because automatically give me string representation. however, when return stringbuilder object, have add .tostring(). true? , why?

also, bit confused following code:

package com.tutorialspoint; import java.lang.*; public class stringbuilderdemo {     public static void main(string[] args) {          stringbuilder str = new stringbuilder("india ");         system.out.println("string = " + str);          // append character stringbuilder         str.append('!');         // convert string object , print         system.out.println("after append = " + str.tostring());          str = new stringbuilder("hi ");          system.out.println("string = " + str);         // append integer stringbuilder         str.append(123);         // convert string object , print         system.out.println("after append = " + str.tostring());     } } 

for different println, code use tostring , other times didn't. why? tried deleting tostring , results same. still necessary use tostring in println?

thanks helping newbie out!

when print object print stream, string representation of object printed, hence tostring invoked.

some classes override object#tostring, amongst stringbuilder does.

hence explicitly invoking tostring stringbuilder unnecessary.

on other hand, other objects don't override tostring. instance, arrays.

when print array, unless using utility such arrays.tostring, you're getting array's class type @ hash code, opposed human-readable representation of contents.