Java: VD về String

public class TVString {

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

    public static int count(String s1, String s2) {
        int n,d = 0;
        n = s1.indexOf(s2);
        while (n >= 0)
        {
            d++;
            n = s1.indexOf(s2,n + s2.length());
        }
        return d;
    }

    public static int countWords(String s)
    {
        int n,d = 0;
        if (s.length()>0) d = 1;
        n = s.indexOf(" ");
        while (n >= 0)
        {   d++;
            n = s.indexOf(" ",n+1); }
        return d;
    }

    public static String ten(String ht)
    {
        int n; String kq;
        ht = ht.trim();
        n = ht.lastIndexOf(" ");
        kq = ht.substring(n+1);
        return kq;
    }

    public static String ho(String ht)
    {
        int n; String kq;
        ht = ht.trim();
        n = ht.indexOf(" ");
        kq = ht.substring(0,n);
        return kq;
    }

    public static String dem(String ht){
        int m,n;
        String kq;
        ht = ht.trim();

        m = ht.indexOf(" ");
        n = ht.lastIndexOf(" ");
        kq = ht.substring(m+1, n);

        return kq;
    }


}