how to assign to String[] from StringBuffer in a loop?
Hi all,
publicclass Test{
public String[] getSJ()
{
String[]jg;
String[]jig;
String[]tg;
String[]result;
Date startTime;
StringBuffer buf =new StringBuffer();
int i;
int j;
int k = -1;
jg ={"g1","g2"};
for( i=0; i < jg.length; i++ )
{
jig ={"1","2","3"};
for( j=0; i < jig.length; j++, k++ )
{
buf.append( jg[i] ).append(":" );
buf.append( jig[j] ).append(":" );
buf.append( Date() );
result[k] = buf.toString();
buf =null;
}
}
}
}
I want to add to result string array by assigning from buf which is StringBuffer in a loop. But what happens after buf = null?
Will the added String be gone?
Or should I just do:
buf = "";
and continue with the loop and the string objects will be preserved? But isn't result just an array of references?
Many thanks,
[1796 byte] By [
navrsalea] at [2007-10-2 6:04:48]
for( j=0; i < jig.length; j++, k++ )
{
buf.append( jg[i] ).append( ":" );
buf.append( jig[j] ).append( ":" );
buf.append( Date() );
result[k] = buf.toString();
buf = new StringBuffer();
}
however, result looks null to me so result[k] will throw NullPointerException unless i've missed something.
String[]tg;//?Date startTime;//?buf.append( Date() );//?
Not quite sure what you are trying to do, but a few mistakes do stand out
In your second loop, you have the condition i<jig.length.
Shouldn't that be j?
buf.append(Date())
Maybe you mean new Date()?
Maybe you want to format a date with a SimpleDateFormat?
- buf = null
If you want to clear the buffer try
buf.setLength(0)
or
buf = new StringBuffer();
You have already copied the value out of the string buffer into a String that is safely stored in the array. That String won't be lost.
Strings are immutable, so once they have a value, they don't change.
Which is the reason that StringBuffers exist - so you have a String you can modify.>
I am not sure I understand correctly. Here is a test program (in real program I call APIs from a library which returns String[] for jg and for jig, i.e they are changing in the loop in runtime.
I tried to put together test program:
import java.util.*;
public class Test {
public void Test() {
}
public String[] getSJ()
{
String[] jg = {"g1", "g2"};
String[] jig = {"1", "2", "3"};
String[]result = new String[50];
StringBuffer buf = new StringBuffer();
int i;
int j;
int k = 0;
for( i=0; i < jg.length; i++ )
{
for( j=0; i < jig.length; j++, k++ )
{
buf.append( jg[i] )
.append( ":" )
.append( jig[j] )
.append( ":" )
.append( new Date() );
result[k] = buf.toString();
buf = null;
}
}
return result;
}
public static void main( String[] args ) {
Testt = new Test();
String[] res = t.getSJ();
for( int i=0; i<res.length; i++ ) {
System.out.println( res[i] );
}
}
}
but when I run it fails in this statement:
buf.append( jg[i] )
.append( ":" )
.append( jig[j] )
.append( ":" )
.append( new Date() );
Exception in thread main
java.lang.NullPointerException
java.lang.String[] Test.getSJ()
Test.java:24
void Test.main(java.lang.String[])
Test.java:38
Wierd!?
And if I change to:
buf.setLength(0);
then it fails with this error:
Exception in thread main
java.lang.ArrayIndexOutOfBoundsException: 3
java.lang.String[] Test.getSJ()
Test.java:24
void Test.main(java.lang.String[])
Test.java:38
Also, I would like not to have to allocate like in:
String[]result = new String[50];
because I do not know how many different Strings in array will be returned by API. Is it possible to dynamically adjust
String[] result
somehow?
Many thanks,>
I just saw evnafets remark regarding loop variable! Now it works, but I'd still like to know if it is possible to dynamically adjust result and not preallocate the size:
g1:1:Fri Nov 25 00:05:44 EST 2005
g1:2:Fri Nov 25 00:05:44 EST 2005
g1:3:Fri Nov 25 00:05:44 EST 2005
g2:1:Fri Nov 25 00:05:44 EST 2005
g2:2:Fri Nov 25 00:05:44 EST 2005
g2:3:Fri Nov 25 00:05:44 EST 2005
null
null
null
null
null
null
Thanks!
in this loop:
for( j=0; i < jig.length; j++, k++ ) {
buf.append( jg[i] )
.append( ":" )
.append( jig[j] )
.append( ":" )
.append( new Date() );
result[k] = buf.toString();
buf = null;
}
you set buf to null at the end of the first iteration. It will throw a NPE
on the second iteration when you try to call append.
> I'd still like to know if it is> possible to dynamically adjust result and not> preallocate the size:You could use one of these[url] http://java.sun.com/j2se/1.4.2/docs/api/java/util/Collection.html[/url]
