About String

[vara prasad]

what is the difference between these two statements

String str="prasad";
String str = new str("prasad");

[jefff willis]

The String class represents character strings. All string literals in Java programs, such as "prasad", are implemented as instances of this class.

Strings are constant; their values cannot be changed after they are created. String buffers support mutable strings. Because String objects are immutable they can be shared. For example:

String str = "prasad";

This creats a string literal, sets it's contents to "prasad" and pases the reference to that literal back to your variable [str].

This however:

String str = new str("prasad");

creates a string literal and sets contents to "prasad" (just like above). But a new string is created and the reference to that literal is passed to it. THEN that new string's referenc is passed to your variable [str].

Since TWO string literals are created in the second example, use the first one in your programs.

[Ernest Friedman-Hill]

Originally posted by jefff willis:

This however:

String str = new str("prasad");

creates...

Actually, of course, this line doesn't even compile. It would be

String str = new String("prasad");

But I think everybody here knows that and this was just a typo.

[George Franciscus]

The explaination lies in understanding the difference between the comparison of an object reference and an object value. This little program explains it in code. Java will set name1 and name2 to the same object reference. Therefore, the first "if" statement evaluates to true, because the "==" is testing that the *references* are the same. However, name3 creates a brand new object with its own object reference. Therefore, the second "if" statement fails because the *references* are different. The third "if" statement evaluates to true because that statement is checking the contents of the String variables, not the references.

The output is as follows...

same
NOT same
equals

Here's the program ...

public class TestString {
 
public static void main(String[] args) {
   new TestString().m();
}
 
public void m() {
   String name1 = "prasad";
   String name2 = "prasad";
   String name3 = new String("prasad"); 
 
   if (name1 == name2) {
      System.out.println("same");
   } else {
      System.out.println("NOT same");
     }

   if (name1 == name3) {
      System.out.println("same");
   } else {
      System.out.println("NOT same");
   }

   if ((name1.equals(name2)) && (name1.equals(name3)))  {
      System.out.println("equals");
   } else {
     System.out.println("not equals");
   }
 }
}

[added code tags - Ilja]
[ January 29, 2005: Message edited by: Ilja Preuss ]