Sudoku solve method using backtracking

Hello all. I am trying to get this program to work using backtracking and now I am at a standstill. I have created the methods checkCol, checkRow, and checkBox and I believe they are correct. I have started writing a solve method and that is where I am stuck. I am not to sure how to implement check methods in solve. Any insight would be great just to get me going. TIA

Code:

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import java.io.*;
import java.util.*;

public class Sudoku {
 
  public static char[][] matrix;
  public static int counter = 0;
  public static String matrixView;
 
 
  public static void main(String[] args) throws FileNotFoundException {
   
    System.out.print("Please enter file name: ");
    Scanner in = new Scanner(System.in);
    String fileName = in.next();
    matrixCreate(fileName);
   
  }
 
  public static void matrixCreate(String fileName) throws FileNotFoundException {
   
    File getFile = new File(fileName);
    Scanner sc = new Scanner(getFile);
    matrixView = "";
   
    while (sc.hasNextLine()){
      matrixView = sc.nextLine();
      counter++;
      System.out.println(matrixView);
    }
   
    sc.close();
   
    matrix = new char[counter] [matrixView.length()];
   
    sc = new Scanner(getFile);
    char getCol;
    for (int rows = 0; rows < counter-1; rows++){
      matrixView = sc.nextLine();
      for (int cols = 0; cols < matrixView.length()-1; cols++){
        getCol = matrixView.charAt(cols);
        matrix[rows] [cols] = getCol;
      }
    }
   
  }
 
  public static boolean checkRow(int r, int check){
   
    for(int x = 0; x <= 5; x++) {
      if(matrix[r][x] == check) return false;
    }
    return true;
   
  }
 
  public static boolean checkCol(int c, int check) {
   
    for(int x = 0; x <=5; x++) {
      if(matrix[x][c] == check) return false;
    }
    return true;
   
  }
 
  public static boolean checkBox(int check, int r, int c) {
   
    for(int x = 2*(r/2); x < 2*(r/2) + 1; x++) {
      for(int y = 3*(c/3); y > 3*(c/3) + 1; y++) {
        if(matrix[x][y] == check) return false;
      }
    }
    return true;
   
  }
 
  public static boolean solve(int r, int c) {
   
    boolean bool = false;
    int a = 0;
   
    // checks boundaries
    if (r < 0 || r > 5 || c < 0 || c > 5) return false;
    if (matrix[r][c] != '0') return true;
    if (matrix[r][c] == 'X') return false;
   
    // record
    matrix[r][c] = 'X';
   
    // navigates through puzzle
    do {
      a++;
      switch(a){
        case 1: bool = solve(r,c+1);
        break;
        case 2: bool = solve(r+1,c);
        break;
        case 3: bool = solve(r-1,c);
        break;
        case 4: bool = solve(r,c-1);
        break;
      }
      if(bool) return true;
    }
   
    while (!bool && a < 4);
    // unrecord
    matrix[r][c] = '0';
    return false;
  }
     
 
 
}

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well ive changed up my code quite a bit and i believe I am getting somewhere. When I call the solve method in main however, it just prints out a bunch of zeros and doesnt solve anything. Anybody see anything?

Code:

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  public static boolean solve(int r, int c) {
    boolean bool = false;
   
    int a = 0; //used for backtracking purposes
    if (r > 5){
      return true;
    }
    else {
      while(matrix[r][c] != 0) {
     
        if(++c > 5) {
     
      c = 0;
    r++;
   
    if(r > 5) return true;
        }
      }
   
   
    for (int check = 1; check < 7; check++)
    {
      if(checkRow(r,check) && checkCol(c,check) && checkBox(check,r,c)){
        matrix[r][c] = check;
        System.out.println(matrixView);
       
        if(c < 5) {
          if (solve(r,c+1)){
            return true;
          }
          else {
            solve(r+1,0);
            a++;
            return true;
           
           
          }
        }
        matrix[r][c] = 0;
      }
    }
    return !bool;
  }
}

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