如何摆脱那个讨厌的领先加号？

Question

I have a code that basically reads from a text file. There is a leading plus sign when it outputs because the answer is printed in a loop. How do I get rid of that singular leading plus sign? All I can think to do is to convert the ENTIRE THING to a string and then take out the first three indexes but that's way too complicated. Is there a simple way to just rearrange the logic and do it?

My code:

    /*
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 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package importtextfiles;

/**
 *
 * @author Hana
 */
import java.io.*;
import java.util.*;
public class InputNumData {
    public static void main(String args[]) throws IOException
    {
        Scanner sf = new Scanner(new File("C:\\Users\\Hana\\SkyDrive\\CompSci\\Programming\\importTextFiles\\meow.txt"));
        int maxIndx = -1; //so the first index is 0

        String text[] = new String[1000];

        while(sf.hasNext()){
            maxIndx++;
            text[maxIndx] = sf.nextLine();
            System.out.println(text[maxIndx]);
        }

        sf.close();

        String answer = "";
        int sum;

        for(int j=0; j<=maxIndx; j++){
            Scanner sc = new Scanner(text[j]);
            sum = 0;
            answer = "";

            while(sc.hasNext()){
                int i = sc.nextInt();
                answer = answer + " + " + i;
                sum = sum + i;
            }
            answer = answer + " = " + sum;
            System.out.println(answer);
        }
    }
}

My output:

run:
12 10 3 5
18 1 5 92 6 8
2 9 3 22 4 11 7
 + 12 + 10 + 3 + 5 = 30
 + 18 + 1 + 5 + 92 + 6 + 8 = 130
 + 2 + 9 + 3 + 22 + 4 + 11 + 7 = 58
BUILD SUCCESSFUL (total time: 0 seconds)

meow.txt:

12 10 3 5
18 1 5 92 6 8
2 9 3 22 4 11 7

Answer 1

Just change this line to

answer = answer.isBlank() ? i : answer + " + " + i;

For more details on how it works refer this .

Answer 2

Take your while loop, and fix the first value:

//Set up first value
int i = sc.nextInt();  //might want to check for hasNext() here 
answer = i;
sum = sum + i;

while(sc.hasNext())
{
   i = sc.nextInt();
   answer = answer + " + " + i;
   sum = sum + i;
}

Answer 3

First thing is not to use concatenation in a loop. Something like:

String result = ""
for (...) {
    result = result + "some additonal data";
}

Creates several intermediate string objects and that's bad practice. It should be replaced with:

StringBuilder sb = new StringBuilder();
for (...) {
    sb.append( "some additional data" );
}
result = sb.toString();

Which allows you to add strings without creating a new string object until you have finished appending.

Now that we are using a StringBuilder , you can have several solutions to the initial plus problem. The first, which would also work with the non-recommended string concatenation, is to keep a flag that tells you if this is the "first operand". Change your while loop to:

StringBuilder sb = new StringBuilder();
boolean firstOperand = true;

while(sc.hasNext()){
    int i = sc.nextInt();
    if ( firstOperand ) {
        firstOperand = false;
    } else {
        sb.append( " + " );
    }
    sb.append( i );
    sum = sum + i;
}
answer = sb.toString();

Another way, which is possible with a StringBuilder is to remove the extra " + " after you finish the loop. In this case, it's better to add the " + " after each operand, so that the extra one will be at the end. It's more efficient to delete from the end of a StringBuilder than from its beginning:

StringBuilder sb = new StringBuilder();

while(sc.hasNext()){
    int i = sc.nextInt();
    sb.append( i ).append( " + " );
    sum = sum + i;
}
if ( sb.length() > 0 ) {
    sb.setLength( sb.length() - 3 );
}
answer = sb.toString();