请帮小弟我写个程序

//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();    }
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请教 char c1 : cs1 这是什么??? 好像以前没有见过啊!!!???
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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
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FOR EACH循环...1.5开始就有的,性能比较好
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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());
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1楼写的好，给分！！
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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();
	}
}