Need help making program more efficient

[cid]

Alright well I have a version of this program which creates a box for inputs >2 The width is supposed to be the integer input, and so is the height. Please tell me if there are any unneccessary lines which I can edit/remove to make the program more concise. Also, the space between the top line and bottom line cannot be asterisks. It must be spaces. Specifically my professor said we needed only three "for loops" but I have four. How can I lose one and keep the program working correctly? We are in the beginning of the class and the furthest we have gotten is for loops.

import java.io.*;
import java.util.*;
class boxes {
public static void main(String[] args) {
String s1 = "";
String s2 = "";
String s4 = "";
int a = 0;
Scanner sc = new Scanner(System.in);
InputStreamReader input = new InputStreamReader(System.in);
BufferedReader reader = new BufferedReader(input);

try {

System.out.println ("Enter a number.");

//start of first line
a = sc.nextInt();
for (int x=0; x<a; x++){
s1 = (s1 + '*');
}
if (a<=2){
System.out.println ("Invalid entry");
System.exit(0);
}
}
System.out.println (s1);
//end of first line







//start of middle portion
for (int x=0; x<a-2; x++){
s2 = (s2 + ' ');

}
String s3 = ('*'+s2+'*');

for (int x=0;x<a-2;x++){
System.out.println (s3);
}
//end of middle portion










//start of last line
for (int x=0; x<a; x++){
s4 = (s4 + '*');
}
System.out.println (s4);
//end of last line

//end of program
}

catch (Exception e){}

}}

[alacn]

edit

encapsulate the a = sc.nextInt(); in a do while loop to check if they entering a number larger than 2

Firstly only declare 2 string variable, one for the top row and one for the middle row, you dont need one for the third because its gonna contain the same data has the first. name them something like String row1; String gap.

then do a do-while loop on the part where you ask to enter a number and then you assign the number. the do while loop will ensure the number is bigger than 2 and if it is not then it will keep repeating the question. Also put a try-catch statment inside the do part of the loop where you write sc.nextInt; and in the catch part write sc.nextLine(), you do the sc.nextLine() otherwise when the code repeats the do-loop it will just keep asking the question in and endless loop.

then after that do one for-statment and thats where you put the asterix in the row1 variable and a space in the gap variable. so you'll end up with like 5 asterixs and 5 spaces.

then you simple System print out the row1 variable
then print out the gap variable in another for loop so that it prints a certain amount of times to make the box the right size
then print out the row1 variable again

you will find that the gap variable will be too large by 2 spaces, so you need to use substring method on it as your printing it off. so research substring

[Fubarable]

Recommendation 1 unrelated to your question:
Never do this:

catch (Exception e){}

except in very specific circumstances when you know what you're doing. Else, if your program throws an exception, you'll never know what caused the exception and why.

Recommendation 2 unrelated to your question:
Please use code tags and decent formatting when posting to this forum. Doing this will make your code much easier to read and will make it much easier for others to help you, and this will likely get you faster and better help. I've taken the liberty of adding code tags to your code, but this unfortunately doesn't help make it more readable as your indentation and code formatting, to be blunt, is terrible.

Recommendation 3 unrelated to your question:
Try to use variable names that make sense, that are "auto-commenting". In other words, instead of

int a;
String s1;
String s2;
String s3:
String s4;

use something like

int sideLength;
String boxTop;
String boxInnerSide;
String boxSide;
String boxBottom;

Recommendation 4 related to your question:
You know that s1 and s4 (boxTop and boxBottom) are exactly the same, right?

[JosAH]

Never use Strings to 'build' them; that is awfully expensive; it doesn't matter much for a box of size, say, 5x6 but for long Strings your method is killing performance and memory. Use a StringBuilder (or StringBuffer) instead; I'd do it like this;

int N, M; // size of the box >= 3
StringBuilder sb= new StringBuilder();
for (int i= 1; i <= N; i++) {
   for (int j= 1; j <= M; j++)
      if ((i == 1) || (i == N) || (j == 1) || (j == M)) // on the side of the box?
         sb.append('*');
      else
         sb.append(' ');
   sb.append('\n');
}
System.out.print(sb.toString());

kind regards,

Jos

[cid]

thanks for the help all and i will try to make my code easier to understand in the future