请帮小弟我写个程序

请帮我写个程序
1。实现字符串“Dot saw I was Tod”的反转
2。找到两个字符串中所有共有的字符

[解决办法]

Java code

//问题1       public String reverse(String str) {        StringBuffer sb = new StringBuffer(str);        sb.reverse();        return sb.toString();    }//问题2    public String check(String str1,String str2) {                List<Character> list = new ArrayList<Character>();        char[] cs1 = str1.toCharArray();        char[] cs2 = str2.toCharArray();        for(char c1 : cs1) {            for(char c2 : cs2) {                if(c1 == c2) {                    list.add(c1);                    break;                }            }        }               //如果你的结果要求不能重复就用set过滤，不要求就返回list.toString();        Set set = new HashSet(list);        return set.toString();    }
[解决办法]
请教 char c1 : cs1 这是什么??? 好像以前没有见过啊!!!???
[解决办法]
请教   char   c1   :   cs1   这是什么???   好像以前没有见过啊!!!???
--从头遍历整个数组，1.5开始有的
[解决办法]
FOR EACH循环...1.5开始就有的,性能比较好
[解决办法]
1:
String str = "Dot   saw   I   was   Tod" ;
StringBuffer str2 =new StringBuffer(str);
  str2.reverse();
System.out.println(str2.toString());

2:
String str = "Dot   saw   I   was   Tod" ;
Char[] str2 = str.toCharArray();
int leng = str2.length;
Char str3 = new Char[leng];
for(int i = leng ; i >0 ; i --)
{
  str3[leng-i]=str2[i-1];
  }
  String str4 = new String(str3);
  System.out.println(str4);
  
3:
  String str = "Dot   saw   I   was   Tod" ;
  StringBuffer sb = new StringBuffer();
  for(int i = str.length()-1; i>=0;i--)
  {
 sb.append(str.CharAt(i));
 }
 System.out.println(sb.toString());
[解决办法]
1楼写的好，给分！！
[解决办法]
package test;

import java.util.ArrayList;
import java.util.List;

public class Test  
{
String s1 = "Dot   saw   I   was   Tod";

String s2 = "Do you know";

List list = new ArrayList();

public void wenTi_1() //问题1
{
System.out.println(new StringBuffer(s1).reverse());
}

public void wenTi_2() //问题2
{
for (int i = 0; i < s1.length(); i++)  
{
for (int j = 0; j < s2.length(); j++)  
{
if (s1.charAt(i) == s2.charAt(j) && s1.charAt(i) != ' ')  
{
list.add(s1.charAt(i));
}
}
}

int temp = 0;
for (int i = 0; i < list.size(); i++)
{
temp = 0;
for (int j = i + 1; j < list.size(); j++)  
{
if (list.get(i).equals(list.get(j)))
{
temp = 1;
}
}
if (temp == 0)  
{
System.out.print(list.get(i) + " ");
}
}
}

public static void main(String[] args)  
{
Test t = new Test();
t.wenTi_1();
t.wenTi_2();
}
}