Java loop not creating string correctly

Question

I'm using a for loop to append an "m" on to a string array, then passing each string to a DDE connection to download a stock quote.

    String[] symbols = {"AUDUSD", "EURUSD", "GBPUSD", "USDJPY"};

    String ibfxSym[] = new String[symbols.length];

    for(int i = 0; i<symbols.length;i++) {
        ibfxSym[i] = symbols[i] + "m";

    }
            // start DDE
    for (int i = 0; i < connections.length; i++) {
        try {
            connections[i].getQuote(ibfxSym[i]);
        } catch (Exception e) {
            System.out.println("error");
        }

That does not work, but if I pass in:

String[] ibfxSym = {"AUDUSDm", "EURUSDm", "GBPUSDm", "USDJPYm"};

instead of the loop it works just fine. I've tried printing each string as it is created in the loop, and they look the same. Is there some weird formatting the loop is adding that I can't see? I even tried:

ibfxSym[i] = String.valueOf(ibfxSym[i].trim());

to see if there was maybe a carriage return or something being appended that I couldn't see. Any ideas about what's going wrong here? Thanks.

are you saying that after the loop, the ibfxSym[] array doesn't contain what you thought it would? There shouldn't be any carriage returns being appended, and the code seems correct, except for the getQuote(ibfxSym[i]) - is the number of connections the same as the array size? — Kylar
– Kylar, Commented Jan 13, 2011 at 19:00
Are you sure connections.length is the same as ibfxSym.length? — Jeremy
– Jeremy, Commented Jan 13, 2011 at 19:00
What do you see when you debug your program line by line? BTW: why do you discard any exception thrown, it may contain helpful information. — Peter Lawrey
– Peter Lawrey, Commented Jan 13, 2011 at 19:03

Jeremy · Accepted Answer · 2011-01-13 19:17:03Z

2

You're not reading from the same array that you're modifying...

    ibfxSym[i] = symbols[i] + "m";

for (int i = 0; i < connections.length; i++) {
    try {
        connections[i].getQuote(ibfxSym[i]);

In other words, you are assuming that i, being derived from iterating over connections, is also a valid index for ibfxSym.

edited Jan 13, 2011 at 19:17

Jeremy

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answered Jan 13, 2011 at 18:58

Falmarri

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5 Comments

Kylar Over a year ago

What? He's assigning to ibfxSym and calling getQuote on it as well.

Jeremy Over a year ago

@Kylar: The point @Falmarri is making is that the OP is creating ibfxSym and then iterating over it with an index derived from iterating over connections, which isn't safe unless you know they are the same length or if the former is smaller.

Kylar Over a year ago

Ahh, that's not what he said. He's implying that he's printing from a different array, not a different index counter. I see what you're saying though.

Justin Ardini Over a year ago

The wording of this answer really confused me as well.

Falmarri Over a year ago

Actually @Kylar is right, I misread the code. But now the answer is that he didn't give us enough information.

CodegistCRest · Accepted Answer · 2011-01-13 19:03:34Z

2

Your loop is working just fine, the connection loop instead would work only if your connections array maps your ibfxSym array though..

answered Jan 13, 2011 at 19:03

CodegistCRest

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Comments

davogotland · Accepted Answer · 2011-01-13 19:01:52Z

1

if

connections.length

is bigger than

ibfxSym.length

or in this case 4, you should get an array index out of bounds exception i think.

answered Jan 13, 2011 at 19:01

davogotland

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Comments

Rcunn87 · Accepted Answer · 2011-01-13 18:59:48Z

0

Have you tried to do this:

for(int i = 0; i<symbols.length;i++) {
    ibfxSym[i] = new String(symbols[i] + "m");

}

answered Jan 13, 2011 at 18:59

Rcunn87

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4 Comments

Jeremy Over a year ago

Calling a String constructor directly is redundant here.

Peter Lawrey Over a year ago

Using + creates a new String, having a new new String shouldn't make much difference.

Kylar Over a year ago

This happens under the hood already (sorta.. a stringbuffer actually gets used in both situations.)

Rcunn87 Over a year ago

I thought so, but wasn't sure when it came to arrays.

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