Java String declaration [duplicate]

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

4 Answers

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.

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.

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

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.