question:String and StringBuffer

[Neha Sawant]

hi,
what is the output?
1)public class RefTest {
public static void main(String [] args) {
String a = "first";
StringBuffer b = new StringBuffer("second"); manipulate(a,b);
System.out.println("a = " + a + ", b = " + b );
}
static void manipulate(String x, StringBuffer y) { String temp = x;
x = y.toString();
y.append(":xtra");
y = new StringBuffer(temp);
}
}
2)public class TestBuffer {
public void myBuf(StringBuffer s, StringBuffer s1) {
s.append(" how are you");
s = s1;
}
public static void main(String args[]) {
TestBuffer tb = new TestBuffer();
StringBuffer s = new StringBuffer("Hello");
StringBuffer s1 = new StringBuffer("doing");
tb.myBuf(s, s1);
System.out.print(s);
}
}

[Roopa Bagur]

1. a = first, b = second:xtra
2. Hello how are you (is the output)

Originally posted by Neha Sawant:
hi,
what is the output?
1)public class RefTest {
public static void main(String [] args) {
String a = "first";
StringBuffer b = new StringBuffer("second"); manipulate(a,b);
System.out.println("a = " + a + ", b = " + b );
}
static void manipulate(String x, StringBuffer y) { String temp = x;
x = y.toString();
y.append(":xtra");
y = new StringBuffer(temp);
}
}
2)public class TestBuffer {
public void myBuf(StringBuffer s, StringBuffer s1) {
s.append(" how are you");
s = s1;
}
public static void main(String args[]) {
TestBuffer tb = new TestBuffer();
StringBuffer s = new StringBuffer("Hello");
StringBuffer s1 = new StringBuffer("doing");
tb.myBuf(s, s1);
System.out.print(s);
}
}

[Neha Sawant]

hi roopa,
thanx for prompt reply.

what significance does
y = new StringBuffer(temp); in question 1
and
s=s1 in question 2 have

[Valentin Crettaz]

this is to demonstrate that all arguments are passed by value. primitive value are copied and object references also !!! Since the reference is copied that means that you can't change the reference the caller provided as argument, but you can manipulate the referenced object though !
thus s=s1 won't change the reference s in the main method, the reference is only changed in the method manipulate but that's all.
HIH
------------------
Valentin Crettaz
Sun Certified Programmer for Java 2 Platform