Java: Number of vowel in a string

I was asked to write a class NumberOcc with these methods:

-method getNbOcc which takes as arguments a string str and a character 'c' and return the number of occurence of the character 'c'.

-method dspNbOcc which displays the value returned by getNbOcc

-method getNbVoy which returns the number of vowel inside a string str

-method dspNbVoy which displays the value returned by getNbVoy

The problem is the value returned by getNbVoy is wrong, example: for str=stackexchange it returns 34 vowels.

public class NumberOcc {
static int count1=0;
static int count2=0;
public static int getNbOcc(String str, char c) {
	for(int i=0;i<str.length();i++) {
		if (str.charAt(i)==c) 
				count1++;}
return count1;
    }
public static void dspNbOcc() {
	System.out.println(count1);
}
public static int getNbVoy(String str) {
	String vowel="aeiouy";
	
	for(int j=0;j<vowel.length();j++) { 
	
		count2+=getNbOcc(str,vowel.charAt(j));}
		return count2;
  }
public static void dspNbVoy() {
	System.out.println(count2);
}
}

TestClass

public class TestNumberOcc {

	public static void main(String[] args) {
    String str="stackexchange";
    NumberOcc.getNbOcc(str, 'e');
    NumberOcc.dspNbOcc();
    NumberOcc.getNbVoy(str);
    NumberOcc.dspNbVoy();
		
		

	}

}

Thanks for helping

Remove the static fields, pass the values to the methods. And use them to display the results. Like,

public static int getNbOcc(String str, char c) {
	int count = 0;
	for (int i = 0; i < str.length(); i++) {
		if (str.charAt(i) == c) {
			count++;
		}
	}
	return count;
}

public static void dspNbOcc(String str, char c) {
	System.out.println(getNbOcc(str, c));
}

public static int getNbVoy(String str) {
	int count = 0;
	char[] vowels = "aeiouy".toCharArray();
	for (char ch : vowels) {
		count += getNbOcc(str.toLowerCase(), ch);
	}
	return count;
}

public static void dspNbVoy(String str) {
	System.out.println(getNbVoy(str));
}

And then testing everything is as simple as

public static void main(String[] args) {
	String str = "stackexchange";
	NumberOcc.dspNbOcc(str, 'e');
	NumberOcc.dspNbVoy(str);
}

the issue is you're not initializing your count1 (nor count2, but that bug doesn't affect anything in this case) at the beginning of your count method... add this line to the beginning of your getNbOcc method before the loop:

public static int getNbOcc(String str, char c) {
    count1 = 0;  // add this line
    for(int i=0;i<str.length();i++) {

The solution is to apply what you did in your countLetterInString function to countVowelsInString. Just remember to use local variables. You will run into issues with static/global variables if the function is called more than once, but local variables will work the same way every time.

public static int countVowelsInString(String str) {
    String vowels = "aeiouy";

    // Move counter into the function
    int numVowels = 0;
    
    for(int j = 0;j<vowel.length();j++) {
        numVowels += getNbOcc(str, vowel.charAt(j));
    }
    return numVowels;
}