String s1 = "Welcome"; // Does not create a new instance
String s2 = new String("Welcome"); // Creates two objects and one reference variable
There is a small difference between both.
Second declaration assignates the reference associated to the constant SOMEto the variable str
First declaration creates a new String having for value the value of the constant SOME and assignates its reference to the variable str.
In the first case, a second String has been created having the same value that SOME which implies more inititialization time. As a consequence, you should avoid it. Furthermore, at compile time, all constants SOMEare transformed into the same instance, which uses far less memory.
As a consequence, always prefer second syntax.
First one will create new String object in heap and str will refer it. In addition literal will also be placed in String pool. It means 2 objects will be created and 1 reference variable.
Second option will create String literal in pool only and str will refer it. So only 1 Object will be created and 1 reference. This option will use the instance from String pool always rather than creating new one each time it is executed.
Source: Stackoverflow.com