public class Test3 {    public static void main(String[] args) {        String s1 = "I am";        String s2 = " a student";        String s3;        String s4;        s3 = s1 + s2;        s4 = s3.substring(7, 8);        //System.out.println(s3);//连接两个字符串        //System.out.println(s4);//求出第7个字符        //System.out.println(s3.indexOf("am"));//找出“am”在该字符串中的位置        //System.out.println(s3.toUpperCase());//把所有字符都变成大写字符        int a = 0,b = 0,c = 0;        for(int i = 0; i < s3.length(); i++){            //48-57代表0-9            if(s3.charAt(i) <= 57 & s3.charAt(i) >= 48){                a++;            }            //65-90代表A-Z,97-122代表a-z            if(s3.charAt(i) <= 90& s3.charAt(i)>=65|s3.charAt(i) <=122&s3.charAt(i) >=97){                b++;            }            if(s3.charAt(i) == ‘ ‘){                c++;            }                    }        System.out.println(a);        System.out.println(b);        System.out.println(c);    }}