Java: Number of specific character reports

I've made a program to count the number of each letters in a phrase

What I want the resulting text to return is

Enter a phrase

"Cow goes to the market"

There are 1 C('s), 3 O('s), 1 W('s), 1 G('s), 3 E('s), 1 S('s), 3 T('s).. /* you get the gist */ in your phrase.

I want the results to be concatenated into a string instead of just a multi-lined report.

import java.util.*;

public class charCount 
{
  public static void main(String[] args)
  {
   Scanner keyboard = new Scanner (System.in);
    //Prompt for user entry
    System.out.println("Enter a phrase: ");
    String letterN = keyboard.nextLine();

    charCount(letterN);
  }


public static int charCount(String letterN)
{ //variable initializations 

    int a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z;
    a = b = c = d = e = f = g = h = i = j = k = l = m = n = o = p = q = r = s = t = u = v = w = x = y = z = 0;

    int total = 0;
    total += 1;

//for loop 
for(int countN = 0; countN < letterN.length(); countN++) {
    switch(letterN.charAt(countN)) {
     case 'a':
        a++;
        break;
     case 'b':
        b++;
        break;
     case 'c':
    c++;
    break;
     case 'd':
    d++;
    break;
     case 'e':
    e++;
    break;
     case 'f':
    f++;
    break;
     case 'g':
        g++;
        break;
     case 'h':
        h++;
        break;
     case 'i':
    i++;
    break;
     case 'j':
    j++;
    break;
     case 'k':
    k++;
    break;
     case 'l':
    l++;
    break;
     case 'm':
        m++;
        break;
     case 'n':
        n++;
        break;
     case 'o':
    o++;
    break;
     case 'p':
    p++;
    break;
     case 'q':
    q++;
    break;
     case 'r':
    r++;
    break;
     case 's':
    s++;
    break;
     case 't':
    t++;
    break;
     case 'u':
    u++;
    break;
     case 'v':
    v++;
    break;
     case 'w':
    w++;
    break;
     case 'x':
    x++;
    break;
     case 'y':
    y++;
    break;
     case 'z':
    z++;
    break;

    }

}

    //Console logs
    System.out.println("Below are the individual character counts for your string");
    System.out.println("A: " + a);
    System.out.println("B: " + b);
    System.out.println("C: " + c);
    System.out.println("D: " + d);
    System.out.println("E: " + e);
    System.out.println("F: " + f);
    System.out.println("G: " + g);
    System.out.println("H: " + h);
    System.out.println("I: " + i);
    System.out.println("J: " + j);
    System.out.println("K: " + k);
    System.out.println("L: " + l);
    System.out.println("M: " + m);
    System.out.println("N: " + n);
    System.out.println("O: " + o);
    System.out.println("P: " + p);
    System.out.println("Q: " + q);
    System.out.println("R: " + r);
    System.out.println("S: " + s);
    System.out.println("T: " + t);
    System.out.println("U: " + u);
    System.out.println("V: " + v);
    System.out.println("W: " + w); 
    System.out.println("X: " + x);
    System.out.println("Y: " + y);
    System.out.println("Z: " + z);

    return total;    
  }  
}

My problem is, I can of course concatenate a System.out.println(); with the int vars but it simply prints the number of letters. I don't know ahead of time what people will type so I need my program to detect if the letter = true and thus returns the character and number inside the report.

I've looked for solutions and cannot find a thing. I can't wrap my mind around this yet and frankly I have no idea how to word this inquiry.

Thank you guys ahead of time