difference between string and string new

1- String objects pool issue

String object is immutable; thats mean when you say

String s = "Mohammed";
s += "El-Adawi";

on runtime this means that a new String "Mohammed El-adawi" is created
and assigned to reference s
and String "Mohammed" now is eligable for gc

why sun have to do that ?, because String literals
(any thing between " " is reccognized by compiler as String literal)
are put by compiler in String pool, then if compilar found the same literal again for example

String s = "abc";
String m = "abc"; // compiler now found the same String literal

compiler will have one copy of "abc" and will assign both s,m to the same String literal, (at run time one object constructed and asigned to s,m)

if m change the String, s will point to the wrong thing, thats why String is immutable.

2- answer to your question

String s = "Marcus"; // One String object is built and assigned to s.

String s2 = new String("Marcus");
/* now compiler found "Marcus" in the pool
so it will not create a new object
new operator creates new object contains 
Marcus at runtime
*/


String s3 = new String("Mohammed Not Marcus");
// compiler adds "Mohammed Not Marcus" to String pool but with no 
// reference assignment, and String object created and assigned to S3 // at runtime 

3- Another thing

String s1 = "abc";
String s2 = "abc"; 
System.out.println(s1 == s2); // true

but

String s1 = "abc";
String s2 = new String ("abc");
System.out.println(s1 == s2); // false 

I hope that is helpfull

visit link
nice explanation with figure that will clear doubts :)
Topic : 2.1 String Literal vs. String Object
http://www3.ntu.edu.sg/home/ehchua/programming/java/J3d_String.html[^]
Happy Coding!
:)

http://www.dotnetspider.com/forum/34649-difference-between-String-string-data-type-c.aspx[^]

Strings are reference type so they refer to the memory location rather than creating a copy.
when we use new operator it will allocate a new memory location from the heap rather than refering to an exsisting location of same String
Here is an example

public class TestString{
public static void main(String[] args){
String a = "Java";
String b = new String(a);
String c = "Java";
System.out.print((a == b)+",");
System.out.print((a == c));
}
}

This will give output as : false,true

Here in first line as "Java" String is not there in pool, a new instance of String with value Java will get created. In second line, we called new, so again a new instance will get created attached to reference b. In third line as "Java" string is already present in the pool, no new instance will be created but String c will make reference to "Java" string already present.
This is also called 'Object Pooling' to enhance pooling.