9.3 输出一个字符串里面的空格，字母还有数字的数目。
public class Test {
public static void main(String[] args) throws IndexOutOfBoundsException {
String a = "I am a student whose age is 20";
shumu(a); //输出字符串空格和字母还有数字的数目。
}
static void shumu(String a) {
int shuzi = 0, zimu = 0, kongge = 0;
char[] c = new char[a.length()];
for (int i = 0; i < a.length(); i++) {
/*下面这句话是java自带的函数，意思是对于某一个字符串,取出某个位置的字符。@马克-to-win*/
c[i] = (char) a.codePointAt(i);
if (c[i] >= '0' && c[i] <= '9') {
shuzi++;
}
if ((c[i] >= 'A' && c[i] <= 'Z') || (c[i] >= 'a' && c[i] <= 'z')) {
zimu++;
}
if (c[i] == ' ') {
kongge++;
}
}

9.6 About string,"I am a teacher"，这个字符串中有多少个字，且分别把每个字打印出来。
/*本题的思路就是，当我有一个字符串，我需要一个一个字符的处理，当下一个字符是个空格的时候,我就知道前面已 经构成了一个完整的字，把它输出出来就好了。如果发现下一个字符不是一个空格的话，我就把这个字符，加到另一个字符串中，逐渐积累那个字符串成为一个完整 的字。*/
public class Test {
static int amount_space = 0; //此变量用来记录空格的数量。the variable named amount_space is used to count the number of the space.
static int flag_Pro = 0; //此变量用来记录现在处理到大字符串中哪一个字符了。this pointer is used to remember the position where we look over.
static String newstring = "I am a teacher";
public static void main(String[] args) {
String outputword = "";
for (int i = flag_Pro; i < newstring.length(); i++) {
if (newstring.substring(i, i + 1).equals(" ")) { //假如newstring.substring(i, i + 1)马克-to-win，取出的字符是个空格,就执行这段程序。
System.out.println(outputword);
outputword = "";
amount_space++;
flag_Pro++; // and next time we will start at a new position
} else {//newstring.substring(i, i + 1);如果不是一个空格，就加到outputword中。
outputword = outputword + newstring.substring(i, i + 1);
flag_Pro++;
}
}
System.out.println(outputword);
outputword = "";System.out.println("共有"+amount_space+"个空格");
System.out.println("共有"+(++amount_space)+"个字");
}
}

public class Sort {
public static void arrangeSequence(char[] strArr,int i){
char temp;
ArrayList list = new ArrayList<>();
if(strArr == null || i> strArr.length|| i<0){
return;
}
else if(i == strArr.length){
//将得到的组合存进ArrayList中
list.add(String.valueOf(strArr));
}
else{
for(int j=i;j
temp = strArr[j];
strArr[j] = strArr[i];
strArr[i] = temp;
//递归调用
arrangeSequence(strArr,i+1);
temp = strArr[j];
strArr[j] = strArr[i];
strArr[i] = temp;
}
}
for(int m=0;m
System.out.println(list.get(m));
}
}
public static void main(String[] args) {
System.out.println("请输入字符串：");
Scanner sc = new Scanner(System.in);
String str = sc.nextLine();
str = str.replaceAll(" ","");
char strArr[] = str.toCharArray();
Arrays.sort(strArr);
arrangeSequence(strArr,0);
}
}

输入:“123545rtyuiewwer21q3q2r2qrqrq23aewqt3qr35y2yhw”,输出:45rtyuiew
import java.io.*;
import java.util.*;
public class DZY22 {
private static String longerStr = "";
    private static int maxLonger = 0;
    public static void getLonger(String target) {
 if(target == null || target.length() == 0) {
            return;
        }
        // 结束递归标识
        boolean out = false;
        StringBuffer sb = new StringBuffer();
        for(int i=0; i<target.length();i++) {
        String chat = target.charAt(i) + "";
            if(!sb.toString().contains(chat)) {
                sb.append(chat);
                //判断是否已经遍历完整个字符串
                if(i == target.length() -1) {
                    longerStr = sb.toString();
                    maxLonger = sb.length();
                    out = true;
                    }
            } else {
            if(maxLonger < sb.length() ) {
                    longerStr = sb.toString();
                    maxLonger = sb.length();
                }
                // 每次递归去掉首字母
                target = target.substring(1);
                // 不可能获得更长的子字符串了
                if(maxLonger == target.length()) {
                    out = true;
                     }
                break;
            }
        }
        if(!out) {
            getLonger(target);
        }
    }
    public static void main(String[] args) {
getLonger("123545rtyuiewwer21q3q2r2qrqrq23aewqt3qr35y2yhw");
        System.out.println("无重复的最长子串为："+longerStr);
        System.out.println("这个子串的长度为："+longerStr.length());
   }
  }