Java String declaration [duplicate]

Question

What is the difference between String str = new String("SOME") and String str="SOME" Does these declarations gives performance variation.

Answer 1

String str = new String("SOME") 

always create a new object on the heap

String str="SOME"  

uses the String pool

Try this small example:

        String s1 = new String("hello");         String s2 = "hello";         String s3 = "hello";          System.err.println(s1 == s2);         System.err.println(s2 == s3); 

To avoid creating unnecesary objects on the heap use the second form.

Answer 2

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.

Answer 3

String s1 = "Welcome"; // Does not create a new instance  
String s2 = new String("Welcome"); // Creates two objects and one reference variable