求字符串中最大重复字串长度程序

Question

我做的就是求一个字符串里面的最大重复字串的长度。比如“do not ask what your country can do for you,ask what you can do for your country” 这个字符串最大字串就是"can do for you"，长度是14，程序我已经做出来了，结果都没有问题。
如下MaxRepStr.java：
import java.util.*;
import java.io.*;
public class MaxRepStr{
public static void main(String[] args) throws IOException{
/*FileReader in=null;
in=new FileReader("D:\\javaEE\\workspace\\HelloTest\\bin\\test.txt");
int c;
List<String> strList=new ArrayList<String>();
while((c=in.read())!=-1){
strList.add(String.valueOf((char)c));
}
String str[]=new String[strList.size()];
for(int j=0,len=strList.size();j<len;j++){
str[j]=strList.get(j);
}*/
String str[]={"d","o"," ","n","o","t"," ","a","s","k"," ","w","h","a","t"," ","y","o","u","r"," ","c","o","u","n","t","r","y"," ","c","a","n"," ","d","o"," ","f","o","r"," ","y","o","u",",","a","s","k"," ","w","h","a","t"," ","y","o","u"," ","c","a","n"," ","d","o"," ","f","o","r"," ","y","o","u","r"," ","c","o","u","n","t","r","y"};
System.out.println();
Map<String,List<Integer>> m=new HashMap<String,List<Integer>>();
for(int i=0,len=str.length;i<len;i++){
if(str[i].equals(" ")) continue;
List<Integer> letter=m.get(str[i]);
if(letter==null){
letter=new ArrayList<Integer>();
letter.add(i);
m.put(str[i],letter);
}else{
letter.add(i);
}
}
System.out.println(m);
int maxCount=0;
int end=0;
for(int i=0,len=str.length;i<len;i++){
if(str[i].equals(" ")) continue;
List<Integer> posList=m.get(str[i]);
for(int posi=posList.indexOf(new Integer(i));posi<posList.size()-1;posi++){
int num=0;
int pos=posList.get(posi+1);
for(int j=i,p=pos;j<len&&p<len;){
if(str[j]==str[p]){
j++;
p++;
num++;
if(maxCount<num){
maxCount=num;
end=p-1;
}
}else break;
}
}
}
System.out.println(maxCount);
for(int i=end-maxCount+1;i<=end;i++){
System.out.print(str[i]);
}
}
}
这样运行结果无误。现在我想从下面文本文件test.txt中读取这个字符串，test.txt内容如下（就一行）：
do not ask what your country can do for you,ask what you can do for your country我改的其实就是注释里面的内容，把字符串从文本中读出来，然后转成这个数组（String str[]={"d","o"," ","n","o","t"," ","a","s","k"," ","w","h","a","t"," ","y","o","u","r"," ","c","o","u","n","t","r","y"," ","c","a","n"," ","d","o"," ","f","o","r"," ","y","o","u",",","a","s","k"," ","w","h","a","t"," ","y","o","u"," ","c","a","n"," ","d","o"," ","f","o","r"," ","y","o","u","r"," ","c","o","u","n","t","r","y"};），然后把之前定义的那个注释掉。得到的是一模一样的数组啊！别的地方都没变，就是结果不对，好郁闷，想好久也没想明白怎么回事，受不鸟了！求高手帮帮忙~~不胜感激。

Answer 1

楼主是想问为什么两种取得str[]的方式下运行结果不对吧是这句出了问题：
if(str[j]==str[p]){应该改成
if (str[j].equals(str[p])) {字符串之间比较，尽量避免用==，只有两个字符串引用指向内存中的同一个字符串对象，==才会返回true。
equals则只要两个字符串的内容相等就会返回true，哪怕他们是内存中的两个字符串对象。你的第一种方式的成功只是一个凑巧，因为如
String str[]={"d","o"," ","n","o","t"," ","a","s","k"," ","w","h","a","t"," ","y","o","u","r"," ","c","o","u","n","t","r","y"," ","c","a","n"," ","d","o"," ","f","o","r"," ","y","o","u",",","a","s","k"," ","w","h","a","t"," ","y","o","u"," ","c","a","n"," ","d","o"," ","f","o","r"," ","y","o","u","r"," ","c","o","u","n","t","r","y"};
这样的定义，每个字符串都在编译的时候放入常量池，而且为相同内容的字符串只创建了一个对象，这样导致==刚好没有问题。
方式二从文件读入，字符串对象在运行时由String.valueOf((char) c)创建，哪怕是相同内容的字符串，在内存中也是不同的对象，用==比较是不会相等的。

Answer 2

用字符数组String str[]={"d","o"," ...
改为 char[] c = {'d', 'o' ...
读取文件，用
String line = new BufferedReader(new FileInputStream(your_file)).readLine();
然后
char c = line.toCharArray();