Detect last iteration in for-each loop in Java

Question

There's a program I'm working on which deals with sentences, words and punctuations. It removes excess spaces from the sentences.

This is my code:

import java.util.*;
class Prog10
{
    static void main()
    {
        Scanner sc=new Scanner(System.in);
        System.out.print("Enter a sentence:");
        String out="";        
        for(String i:sc.nextLine().split("[\\s]"))
            out+=i+(<last-iteration-condition>?"":" ");  //Using regex to clean excess spaces
        System.out.print(out);
    }
}

I'm wanting to detect the last iteration without any new additions to code except for the boolean condition. No as an answer would also suffice.

It wouldn't: it must be at least 30 character long. But No is the correct answer. — Maurice Perry
– Maurice Perry, Commented Feb 20, 2018 at 7:18
Thanks, that was quick. By 30 characters long, are you referring to the additional code required? — Utkarsh Verma
– Utkarsh Verma, Commented Feb 20, 2018 at 7:21

Andy Turner · Accepted Answer · 2018-02-20 07:35:38Z

1

There is no way to determine if it is the last iteration of the loop, directly.

If you know the length of the array/Iterable that you are iterating, you can count the number of iterations, and do something when you know it is the last one, but this somewhat defeats the point of the enhanced for loop.

It is pretty easy to determine if it is the first iteration of the loop, however:

boolean isFirstIteration = true;
for (String i : someIterable) {
  // Do stuff.

  isFirstIteration = false;
}

You can use this in your case, by appending the space first:

String delim = "";
for(String i:sc.nextLine().split("[\\s]")) {
  out += delim + i;      
  delim = " ";
}

The delim variable is initially the empty string, so you don't insert anything on the first iteration. However, it is then set to a space, so a space is inserted on every subsequent iteration, then your i string.

Mind you, String.join(" ", sc.nextLine().split(...)) would be easier.

edited Feb 20, 2018 at 7:35

answered Feb 20, 2018 at 7:24

Andy Turner

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4 Comments

Utkarsh Verma Over a year ago

That does add a bit of code, for example, the extra braces and a new String variable which I wanted to avoid but I think I'll have to use this method.

Andy Turner Over a year ago

@Utkarsh if you're worried about adding one variable, you should really adopt a more efficient method of concatenating strings.

Utkarsh Verma Over a year ago

Thanks, I will look into it :smile:.

kutschkem Over a year ago

+1 getting used to checking for the first instead of the last iteration is very helpful when you start to code declaratively, for example concatenate strings in SQL.

Utkarsh Verma · Accepted Answer · 2018-02-20 07:54:38Z

0

This is what I've come up with:

String out="";
for(String i:sc.nextLine().split("[\\s]"))        
    out+=(out.isEmpty()?"":" ")+i;  
System.out.print(out);

answered Feb 20, 2018 at 7:54

Utkarsh Verma

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Comments

Ferrybig · Accepted Answer · 2018-02-20 09:00:22Z

0

Instead of re-inventing the wheel, you should use a StringJoiner to join the strings together.

StringJoiner out = new StringJoiner(" ");        
for(String i:sc.nextLine().split("[\\s]"))
    out.add(i);
System.out.print(out.toString());

answered Feb 20, 2018 at 9:00

Ferrybig

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1 Comment

Utkarsh Verma Over a year ago

Nice suggestion!

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