confused with String Equality

[geeta vemula]

I got these from

http://www.angelfire.com/or/abhilash/quiz/quiz4.html

1. Read this piece of code carefully

if("String".replace('g','G') == "String".replace('g','G'))
System.out.println("Equal");
else
System.out.println("Not Equal");

Answers

the code will compile an print "Equal".
the code will compile an print "Not Equal".
the code will cause a compiler error
Ans b


2. Read this piece of code carefully

if("String".replace('T','t') == "String")
System.out.println("Equal");
else
System.out.println("Not Equal");

Answers

the code will compile an print "Equal".
the code will compile an print "Not Equal".
the code will cause a compiler error
Ans a

3. Read this piece of code carefully

if("String".replace('t','t') == "String")
System.out.println("Equal");
else
System.out.println("Not Equal");

Answers

the code will compile an print "Equal".
the code will compile an print "Not Equal".
the code will cause a compiler error
Ans a

When it gives equal and when not? very much confused with this. Kindly help me.

Thanks
Geeta Vemula

[James Tharakan]

The replace method returns a new string object IF AND ONLY IF there is any change in the actually string.

Look at the replace method implementation.

public String replace(char oldChar, char newChar) {
if (oldChar != newChar) {
    int len = count;
    int i = -1;
    char[] val = value; /* avoid getfield opcode */
    int off = offset;   /* avoid getfield opcode */
 
    while (++i < len) {
if (val[off + i] == oldChar) {
    break;
}
    }
    if (i < len) {
char buf[] = new char[len];
for (int j = 0 ; j < i ; j++) {
    buf[j] = val[off+j];
}
while (i < len) {
    char c = val[off + i];
    buf[i] = (c == oldChar) ? newChar : c;
    i++;
}
return [B]new[/B] String(0, len, buf);
    }
}
return [B]this[/B];
    }

[ December 31, 2008: Message edited by: James Tharakan ]

[Vinod Kumar Kommineni]

Hi Geetha according to what James had posted I feel that in 2nd and 3rd code blocks there is no change in the String
2nd -because T is not present in String at all,
3rd- since old and new variable are equal.

But any comparison of String's with == is not encouraged instead if you use string1.equals(string2) it will give true results.