String concat

[Thiru Thangavelu]

why concat is failing here?

public class Test {
public static void main(String args[]) {
 StringBuffer sb = new StringBuffer("abc");
 String s = new String("abc");
 sb.append("def");
 s.append("def");
 sb.insert(1, "zzz");
 s.concat(sb);
 s.trim();
}
}

[ June 12, 2002: Message edited by: Thiru Thangavelu ]

[Brian Lugo]

Did you compile and run the program?
If yes, what do you think is the answer?
Brian

[Thiru Thangavelu]

I think there is no method in String class as concat(StringBuffer). That's why the error is. Isn't?

[geetha nagarajan]

String class has a concat method that takes only String as parameter.
So,only concat(String) will work.
It does not work with any other parameter.
Am i right?

[Swati Gupta]

Even the line s.append("def"); will error out as String class does not have append.

[Jie Zhou]

Even the line s.append("def"); will error out as String class does not have append.

Actually s.append("def") will not cause error.
The overloaded method
StringBuffer append(String str)
appends the string "def" to this string buffer.

[Thomas Paul]

Originally posted by Jie Zhou:

Actually s.append("def") will not cause error.
The overloaded method
StringBuffer append(String str)
appends the string "def" to this string buffer.

But s is a String and String does not have an append method, overloaded or not!

[Jie Zhou]

Thanks, Thomas.
I thought s is a StringBuffer variable, but it is a Stirng.

[Bonnie Beach-Morin]

Even if the programmer used

s.concat(sb.toString())

(and s.append("def) were removed), the code would not work as intended. The String class is immutable, so any call to the concat method returns a new String object and does not modify the original String object. The programmer would need to do something like

s = s.concat(sb.toString());

[Gautam Sewani]

The last reply was the only correct reply!