import java.util.Scanner;
public class CountLetters {

public static void main(String[] args) {
Scanner in=new Scanner(System.in);
System.out.print("请出入你要得字符串:");
String str=in.nextLine();
String[] letters = {"a","e","i","o","u"};
System.out.println(getCountLetters(str,letters));
}
public static int getCountLetters(String countStr,String[] letters){
int returnNum=0;
for(int i=0;i<countStr.length();i++){
for(int j=0;j<letters.length;j++){
if(letters[j].equalsIgnoreCase(countStr.substring(i,i+1))){
returnNum++;
}
}
}
return returnNum;
}

帮我注释一下这个程序，还有帮我解释下System.out.println(getCountLetters(str,letters));
这句话是什么意思啊。。getcountletters是什么，请详细说明，谢谢啦