What is the difference between String str1 = "hello"; and String str2 = new String ("hello"); in java?

What is the difference between String str1 = "hello"; and String str2 = new String ("hello"); in java?

I know the str2 is a object, but what about str1?

I mean for example:

if both of them are object, but why

if(str1.toString() == str2.toString())

does not result a true boolean?