I don't know why this is fiving me an error, can someone please help

public class MyProgram
{
    public static void main(String[] args)
    {
        public static void main(String[] args)
    {
        System.out.println("Problem 1: " + isLetterA('a'));
        System.out.println("Problem 2: " + hasTwoA("computer"));
        System.out.println("Problem 3: " + isVowel('e'));
        System.out.println("Problem 4: " + numVowels("computers"));
        System.out.println("Problem 5: " + evenChars("computerScience", 'e', 's'));
        System.out.println("Problem 6: " + twoInARow("book", 'o'));
        System.out.println("Problem 7: " + capitalizeVowels("hello"));
        System.out.println("Problem 8: " + longestWord("hello how are you "));
        System.out.println("Problem 9: " + containsPrefix("abXYabc", 2));
    }//end main
    //1
    public static boolean isLetterA(char letter)
    {
        return letter == 'a';
    }//end 1
   
    //2 - change n do using char array
    public static boolean hasTwoA (String s)
    {
        int twoA = 0;
        boolean hasA = false;
        for (int i = 0; i < s.length(); i++)
        {
            if ((s.charAt(i)) == ('a'))
            {
                twoA++;
                if (twoA == 2)
                {
                    hasA = true;  
                }
            }
        }
        return hasA;
    }//end 2
   
    //3
    public static boolean isVowel(char letter)
    {
        if (letter == ('a') || letter == ('e') || letter == ('i') || letter == ('o') || letter == ('u') || letter == ('A') || letter == ('E') || letter == ('I') || letter == ('O') || letter == ('U'))
        {
            return true;
        }
        return false;
    }//end 3
   
    //4
    public static int numVowels(String s)
    {
        char[] chars = s.toCharArray();
        int numOfVowels = 0;
        for (int i = 0; i < chars.length; i++)
        {
            if (isVowel(chars[i]) == true)
            {
                numOfVowels++;
            }
        }
        return numOfVowels;
    }//end 4
   
    //5
    public static boolean evenChars(String s, char a, char b)
    {
        char[] chars = s.toCharArray();
        int numOfA = 0;
        int numOfB = 0;
        for (int i = 0; i < chars.length; i++)
        {
            if (s.charAt(i) == a)
            {
                numOfA++;
            }
            if (s.charAt(i) == b)
            {
                numOfB++;
            }
        }    
        return numOfA == numOfB;
    }//end 5
   
    //6
    public static boolean twoInARow(String s, char a)
    {
        char[] chars = s.toCharArray();
        boolean result = false;
        for (int i = 1; i < chars.length; i++)
        {
            if (s.charAt(i) == a)
            {
                if (s.charAt(i - 1) == a)
                {
                    result = true;
                    break;
                }
            }
        }
        return result;
    }//end 6
   
    //7
    public static String capitalizeVowels(String s)
    {
        char[] chars = s.toCharArray();
        String vowels = "";
        for (int i = 0; i < chars.length; i++)
        {
            if (isVowel(chars[i]) == true)
            {
                chars[i] = Character.toUpperCase(chars[i]);
            }
        }
        String answer = new String(chars);
        return answer;
    }//end 7
   
    //8
    public static String longestWord(String s)
    {
        String[] words = s.split(" ");
        int answer = 0;
        for (int i = 1; i < words.length; i++)
        {
            if (words[i].length() > words[answer].length())
            {
                answer = i;
            }
        }
        return words[answer];
    }
   
    //9
    public static boolean containsPrefix(String s, int n)
    {        
        boolean hasPrefix = false;
        String prefix = s.substring(0,n);
        String excludePrefix = s.substring(n);
        if (excludePrefix.indexOf(prefix) > -1)
        {
            hasPrefix = true;
        }
        return hasPrefix;
    }
}

MyProgram.java:5: error: illegal start of expression
        public static void main(String[] args)
        ^

MyProgram.java:5: error: illegal start of expression
        public static void main(String[] args)
               ^
MyProgram.java:5: error: ';' expected
        public static void main(String[] args)
                     ^
MyProgram.java:5: error: '.class' expected
        public static void main(String[] args)
                                         ^
MyProgram.java:5: error: ';' expected
        public static void main(String[] args)
                                             ^
MyProgram.java:18: error: illegal start of expression
    public static boolean isLetterA(char letter)
    ^
MyProgram.java:18: error: illegal start of expression
    public static boolean isLetterA(char letter)
           ^
MyProgram.java:18: error: ';' expected
    public static boolean isLetterA(char letter)
                 ^
MyProgram.java:18: error: '.class' expected
    public static boolean isLetterA(char letter)
                                         ^
MyProgram.java:18: error: ';' expected
    public static boolean isLetterA(char letter)
                                               ^
MyProgram.java:24: error: illegal start of expression
    public static boolean hasTwoA (String s)
    ^
MyProgram.java:24: error: illegal start of expression
    public static boolean hasTwoA (String s)
           ^
MyProgram.java:24: error: ';' expected
    public static boolean hasTwoA (String s)
                 ^
MyProgram.java:24: error: ')' expected
    public static boolean hasTwoA (String s)
                                         ^
MyProgram.java:24: error: illegal start of expression
    public static boolean hasTwoA (String s)
                                           ^
MyProgram.java:24: error: ';' expected
    public static boolean hasTwoA (String s)
                                            ^
16 errors