With StringBuffer

import java.util.*;
public class Project1 {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        System.out.print("Input n: ");
        int number = scan.nextInt();
        int n =number;
        int m =1;
        int ArrayCount =0;
        StringBuffer line= new StringBuffer("");
        //String line = new String("");
        String lineFirst="";
        String lineReplace="";
        String [] reverse = new String [number];
        if(number==1){
            System.out.println("1");
        }else
        for(int i =1;i<=(2*number)-1;i++){ //Generate first and last line
            lineFirst+=number;
        }
        line.append(lineFirst); // make line = linefirst
        System.out.println(line); //print first line
            for(int i =1;i<=number-1;i++){
                for(int j =m;j<line.length()-1;j++){ //Generate replace words
                    lineReplace += n-1;
                }
            line = line.replace(i,line.length()-i,lineReplace);  //Replace words in substring
            System.out.println(line);
            reverse[ArrayCount] = line.toString(); //Add to array for reverse
            ArrayCount++;
            lineReplace="";
            n--;
            m+=2;
            }
        for(int k=ArrayCount-2;k>=0;k--){  //Reverse line
            System.out.println(reverse[k]);
        }
        System.out.println(lineFirst); //print last line
    }

}