How to append string dynamically? [duplicate]

Question

Hi my requirement is to produce following string:

qid<> 0 And qid<> 1 And qid<> 2 And qid<> 3 And qid<> 4 And qid<> 5 And qid<> 6 And qid<> 7 And qid<> 8 And qid<> 9

So I did like this:

import java.util.*; import java.lang.*; import java.io.*; /* Name of the class has to be "Main" only if the class is public. */ class Ideone { public static void main (String[] args) throws java.lang.Exception { // your code goes here String deleteQids="qid<> "; String deleteqidString1=""; for(int i=0;i<10;i++) { deleteqidString1+=deleteQids+i +" And "; } System.out.println(deleteqidString1); } }

http://ideone.com/dpFfxF

But at the end And appears.

Can anybody please tell me how to get rid of this?

Add a condition to check if current iteration is last, and add "And" only if conditions is false. — shree.pat18
– shree.pat18, Commented Jun 12, 2014 at 7:35
Note that C# has a handy string.Join method that you can add " and " inbetween each element of a list and this answer gives ideas for doing the same in java: stackoverflow.com/questions/187676/… — weston
– weston, Commented Jun 12, 2014 at 7:40

Mureinik · Accepted Answer · 2014-06-12 07:35:18Z

You could just handle the first occurrence explicitly:

String deleteqidString1 = deleteQids+i; for(int i=1; i < 10; i++) { deleteqidString1 += " And " + deleteQids + i; }

EDIT:
As noted in the comments, a StringBuilder is the right tool for dynamically building tools. (This doesn't effect the logic of the solution, though):

StringBuilder deleteqidString1 = new StringBuilder(deleteQids).append(i); for(int i=1; i < 10; i++) { deleteqidString1.append(" And ").append(deleteQids).append(i); }

My only criticism of this approach is it assumes that there is at least one "qid"
@MadProgrammer yup, agreed. The OP seems to assume this limitation, so I went along. The solution could easily be improved to check handle the case of 0 "qid"s.

MadProgrammer · Accepted Answer · 2014-06-12 07:35:36Z

You could simply use String#substring to remove the last " And " from the String, but a more efficent method would to use a StringBuilder and "prefix" " And " to it when the index is greater than 0, for example

String deleteQids = "qid<> "; StringBuilder sb = new StringBuilder(128); for (int i = 0; i < 10; i++) { if (i > 0) { sb.append(" And "); } sb.append(deleteQids).append(i); } System.out.println(sb.toString());

Which ends up printing something like...

qid<> 0 And qid<> 1 And qid<> 2 And qid<> 3 And qid<> 4 And qid<> 5 And qid<> 6 And qid<> 7 And qid<> 8 And qid<> 9

What is the reason to apply an initial capacity to the StringBuilder? Is it faster if you know that the specified size will be used anyway?
@brimborium Yes, like ArrayList, StringBuilder uses a char array internally, so when it reaches it's limit, the array needs to be resized, initialising the initial capacity reduces the potential overhead of this operation

Kasper Ziemianek · Accepted Answer · 2014-06-12 07:42:09Z

If you operates much on strings always use StringBuilder because it's more efficient.

 int qids = -1; StringBuilder sb = new StringBuilder(); if(qids>=0) { for(int i=0;i<qids-1;i++) { sb.append("qid<> "); sb.append(i); sb.append(" And "); } sb.append("qid<> "); sb.append(qids); } System.out.println(sb.toString());

Nirav Prajapati · Accepted Answer · 2014-06-12 07:44:12Z

if your iteration is fixed upto 10 then

than try this one it may help this is not optimum way to do this but still you can get what you want

if iteration is fixed to 10

import java.util.*; import java.lang.*; import java.io.*; /* Name of the class has to be "Main" only if the class is public. */ class Ideone { public static void main (String[] args) throws java.lang.Exception { // your code goes here String deleteQids="qid<> ";String deleteqidString1=""; for(int i=0;i<10;i++) { if(i==9) { deleteqidString1+=deleteQids+i ; } else { deleteqidString1+=deleteQids+i +" And "; } } System.out.println(deleteqidString1); } }

sujithvm · Accepted Answer · 2014-06-12 09:31:33Z

The code snippet given below does the job. It adds 'And' for every iteration except for the last one ie. when i equals 9.

String deleteQids="qid<> "; String deleteqidString1=""; for(int i=0;i<10;i++) { deleteqidString1 += deleteQids + i ; if (i < 9) deleteqidString1 += " And "; }

Please point the OP what you have done, and explain what your code is doing.

PKlumpp · Accepted Answer · 2014-06-12 07:35:10Z

You better use a StringBuilder for this. And then, you have to find a system to know where to put your "And".

Here is some hint:

An "And" comes after an Integer. (But not after the last one)
An "And" is followed by a "qid<>"

Combine these conditions, and you can build your String.

jwenting · Accepted Answer · 2014-06-12 07:36:10Z

Either change your logic to not append that "And" if you're in the last iteration of the loop, or after you are done looping modify the String to remove it.
Those are basically your 2 options, which you'd choose would depend on personal preference and the exact application logic.
In this simple case I'd elect the first, in a more realistic scenario where the String is constructed using a StringBuilder and an Iterator over some Collection the second option is often easier to implement and certainly easier to read.

So something along the lines of

deletequidString1 += deleteQuids+1; if (i < 10) deleteQuidString1 += " And ";

would be your best bet here.

premji · Accepted Answer · 2014-06-12 07:55:02Z

Use this code

 String deleteQids="qid<> "; String deleteqidString1=""; for(int i=0;i<10;i++) { if(i!=9) { deleteqidString1+=deleteQids+i +" And "; } else { deleteqidString1+=deleteQids+i +""; } } System.out.println(deleteqidString1); }

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