为什么程序中有退出的代码java还要抛出异常呢？

[ekisstherain]

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
public class FindMaxRepeatString
{
/*print the string
*the parameter explain is the declaring words,
*and the string is for printing
*/
public static void printString(String explain,String str)
{
System.out.print(explain);
System.out.println(str);
}

//the function is output integer
public static void printString(String explain,int Int)
{
System.out.print(explain);
System.out.println(Int);
}
//the main function
public static void main(String args[])
{
BufferedReader buf=new BufferedReader(new InputStreamReader(System.in));
String str = null;//define a str for save the input string
String sub=null; //safe a sub string from the str
System.out.println("Input a string :");
try
{
str=buf.readLine();
}
catch(IOException e)
{
System.err.println("Input error:"+e.getMessage());
}

//print the string which you input
printString("the str you input is:",str);
//当str=null时，退出程序
if(str==null)
System.exit(0);

int position=0; //record the start point of the sub string
int maxCount=0; //Save the max equal count
//Save the length of the sub string which is repeat max in string
int maxLen=1;
sub=str.substring(0,0);
int i=1;
try
{
// TODO: handle exception
for(int k=0;k<str.length()-1;k++) //k表示从第几位开始比较
{
for(i=1;i<=str.length()/2&&(k+i)<str.length();i++)
{
sub=str.substring(k, k+i);
System.out.println("the sub is :"+sub);
int count=0;
for(int j=i+k;sub.length()<=str.length()-j;j+=sub.length())
{
String s=str.substring(j,j+i);
System.out.println("the s is :"+s);
if(sub.compareTo(s)==0)
count++;
else
break;
}
if(maxCount<count||(count>0&&maxCount==count&&maxLen<sub.length()))
{
maxCount=count;
position=k;
System.out.println("position is :"+position);
maxLen=sub.length();
}
}
}
}
catch(NullPointerException e)
{
System.err.println("Main: Null point error:"+e.getMessage());
}
//这句代码抛出异常
sub=str.substring(position, position+maxLen);
printString("the start of the sub in the string is:", position);
printString("the length of the sub is:", maxLen);
printString("the compare most count is:", maxCount);
printString("The sub string repeat most is:", sub);
}
}

我就是不明白为什么
我还成了这样:
if(str!=null)
sub=str.substring(position, position+maxLen);
它还是要抛出异常，为什么呢？？？
另外：我用str.trim();为什么不能去掉空格呢？？？
还用过了str.replaceAll(" ","");
都没用啊???这又是为什么啊
谁可以帮忙解释下
谢谢啦...

[ekisstherain]

设置成代码形式：

import java.io.BufferedReader; 
import java.io.InputStreamReader; 
import java.io.IOException; 
public class FindMaxRepeatString 
{ 
/*print the string 
*the parameter explain is the declaring words, 
*and the string is for printing 
*/ 
public static void printString(String explain,String str) 
{ 
System.out.print(explain); 
System.out.println(str); 
} 

//the function is output integer 
public static void printString(String explain,int Int) 
{ 
System.out.print(explain); 
System.out.println(Int); 
} 
//the main function 
public static void main(String args[]) 
{ 
BufferedReader buf=new BufferedReader(new InputStreamReader(System.in)); 
String str = null;//define a str for save the input string 
String sub=null; //safe a sub string from the str 
System.out.println("Input a string :"); 
try 
{ 
str=buf.readLine(); 
} 
catch(IOException e) 
{ 
System.err.println("Input error:"+e.getMessage()); 
} 

//print the string which you input 
printString("the str you input is:",str); 
                  //当str=null时，退出程序 
if(str==null) 
System.exit(0); 

int position=0; //record the start point of the sub string 
int maxCount=0; //Save the max equal count 
//Save the length of the sub string which is repeat max in string 
int maxLen=1; 
sub=str.substring(0,0); 
int i=1; 
try 
{ 
// TODO: handle exception 
for(int k=0;k <str.length()-1;k++) //k表示从第几位开始比较 
{ 
for(i=1;i <=str.length()/2&&(k+i) <str.length();i++) 
{ 
sub=str.substring(k, k+i); 
System.out.println("the sub is :"+sub); 
int count=0; 
for(int j=i+k;sub.length() <=str.length()-j;j+=sub.length()) 
{ 
String s=str.substring(j,j+i); 
System.out.println("the s is :"+s); 
if(sub.compareTo(s)==0) 
count++; 
else 
break; 
} 
if(maxCount <count||(count>0&&maxCount==count&&maxLen <sub.length())) 
{ 
maxCount=count; 
position=k; 
System.out.println("position is :"+position); 
maxLen=sub.length(); 
} 
} 
} 
} 
catch(NullPointerException e) 
{ 
System.err.println("Main: Null point error:"+e.getMessage()); 
} 
                  //这句代码抛出异常 
sub=str.substring(position, position+maxLen); 
printString("the start of the sub in the string is:", position); 
printString("the length of the sub is:", maxLen); 
printString("the compare most count is:", maxCount); 
printString("The sub string repeat most is:", sub); 
} 
} 

[ekisstherain]

import java.io.BufferedReader; 
import java.io.InputStreamReader; 
import java.io.IOException; 
public class FindMaxRepeatString 
{ 
/*print the string 
*the parameter explain is the declaring words, 
*and the string is for printing 
*/ 
public static void printString(String explain,String str) 
{ 
System.out.print(explain); 
System.out.println(str); 
} 

//the function is output integer 
public static void printString(String explain,int Int) 
{ 
System.out.print(explain); 
System.out.println(Int); 
} 
//the main function 
public static void main(String args[]) 
{ 
BufferedReader buf=new BufferedReader(new InputStreamReader(System.in)); 
String str = null;//define a str for save the input string 
String sub=null; //safe a sub string from the str 
System.out.println("Input a string :"); 
try 
{ 
str=buf.readLine(); 
} 
catch(IOException e) 
{ 
System.err.println("Input error:"+e.getMessage()); 
} 

//print the string which you input 
printString("the str you input is:",str); 
                  //当str=null时，退出程序 
if(str==null) 
System.exit(0); 

int position=0; //record the start point of the sub string 
int maxCount=0; //Save the max equal count 
//Save the length of the sub string which is repeat max in string 
int maxLen=1; 
sub=str.substring(0,0); 
int i=1; 
try 
{ 
// TODO: handle exception 
for(int k=0;k <str.length()-1;k++) //k表示从第几位开始比较 
{ 
for(i=1;i <=str.length()/2&&(k+i) <str.length();i++) 
{ 
sub=str.substring(k, k+i); 
System.out.println("the sub is :"+sub); 
int count=0; 
for(int j=i+k;sub.length() <=str.length()-j;j+=sub.length()) 
{ 
String s=str.substring(j,j+i); 
System.out.println("the s is :"+s); 
if(sub.compareTo(s)==0) 
count++; 
else 
break; 
} 
if(maxCount <count||(count>0&&maxCount==count&&maxLen <sub.length())) 
{ 
maxCount=count; 
position=k; 
System.out.println("position is :"+position); 
maxLen=sub.length(); 
} 
} 
} 
} 
catch(NullPointerException e) 
{ 
System.err.println("Main: Null point error:"+e.getMessage()); 
} 
                  //这句代码抛出异常 
sub=str.substring(position, position+maxLen); 
printString("the start of the sub in the string is:", position); 
printString("the length of the sub is:", maxLen); 
printString("the compare most count is:", maxCount); 
printString("The sub string repeat most is:", sub); 
} 
} 

[ekisstherain]

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
public class FindMaxRepeatString
{
/*print the string
*the parameter explain is the declaring words,
*and the string is for printing
*/
public static void printString(String explain,String str)
{
System.out.print(explain);
System.out.println(str);
}

//the function is output integer
public static void printString(String explain,int Int)
{
System.out.print(explain);
System.out.println(Int);
}
//the main function
public static void main(String args[])
{
BufferedReader buf=new BufferedReader(new InputStreamReader(System.in));
String str = null;//define a str for save the input string
String sub=null; //safe a sub string from the str
System.out.println("Input a string :");
try
{
str=buf.readLine();
}
catch(IOException e)
{
System.err.println("Input error:"+e.getMessage());
}

//print the string which you input
printString("the str you input is:",str);
//当str=null时，退出程序
if(str==null)
System.exit(0);

int position=0; //record the start point of the sub string
int maxCount=0; //Save the max equal count
//Save the length of the sub string which is repeat max in string
int maxLen=1;
sub=str.substring(0,0);
int i=1;
try
{
// TODO: handle exception
for(int k=0;k <str.length()-1;k++) //k表示从第几位开始比较
{
for(i=1;i <=str.length()/2&&(k+i) <str.length();i++)
{
sub=str.substring(k, k+i);
System.out.println("the sub is :"+sub);
int count=0;
for(int j=i+k;sub.length() <=str.length()-j;j+=sub.length())
{
String s=str.substring(j,j+i);
System.out.println("the s is :"+s);
if(sub.compareTo(s)==0)
count++;
else
break;
}
if(maxCount <count||(count>0&&maxCount==count&&maxLen <sub.length()))
{
maxCount=count;
position=k;
System.out.println("position is :"+position);
maxLen=sub.length();
}
}
}
}
catch(NullPointerException e)
{
System.err.println("Main: Null point error:"+e.getMessage());
}
//这句代码抛出异常
sub=str.substring(position, position+maxLen);
printString("the start of the sub in the string is:", position);
printString("the length of the sub is:", maxLen);
printString("the compare most count is:", maxCount);
printString("The sub string repeat most is:", sub);
}
}

[「已注销」]

不好意思,刚刚中午休息...
对于你第二的问题,想要消除所有的空格 对吧？
我这里有一个方法,就是用空字符去替代空格
代码如下
str=str.replace(" ","");
你把这句话加在 printString("the str you input is:",str); 这句前就行了

可能还有其他方法,那就你自己再去琢磨琢磨

[「已注销」]

你说你用过replaceAll 但不行 我想你一定是太粗心了 这个方法返回值是String类型的结果 而不是直接作用在字符串上 下次小心噢！ 呵呵

[「已注销」]

你说你用过replaceAll 但不行 我想你一定是太粗心了 这个方法返回值是String类型的结果 而不是直接作用在字符串上 下次小心噢！ 呵呵

[ekisstherain]

呵呵， 不好意思啦，我就是那么粗心啦
答案 就是
str=str.replaceAll(" ","");
这个是把所有的空格都去掉
我还试了一下str=str.trim();
这个只能去掉开头和最后的空格，中间的去不了
比如" a b c "
用了trim后变成"a b c"
就这样了

谢谢各位细心帮忙啦...
分数不多，将就着分啦^_^

[「已注销」]

完全不明白你想要实现什么效果

[tangjun685]

我来顶

[「已注销」]

判断改为 if (null == str || "".equals(str))
你可以调试跟一下程序 就会发现当回车的时候 str="" 而不是NULL

[火龙果被占用了]

把代码格式缩进整理好是对看帖者的一种尊重，也能很好地解决问题！

[BearKin]

[Quote=引用 8 楼 bao110908 的回复:]
把代码格式缩进整理好是对看帖者的一种尊重，也能很好地解决问题！
[/Quote]

缩进不缩进不重要 代码这么长 发出来吓唬我们啊..

[youjianbo_han_87]

说一下，到底要实现什么功能，在做什么的时候出错了，楼主这么长的代码，我真的没有很多时间去看啊。

[阿奇XS]

linux+oracle+j2ee 群：87923477

[ekisstherain]

代码的功能就是从控制台输入str串，找出串中最大的重复子串，就这样，但是当str=null时，就是说我什么也没有输入来找子串，这样的情况会抛出异常，为什么呢？？？
另外，我想去掉str串中的空格，怎么用才能去str串中的所有空格呢???
就两个问题，代码是有点长，不过对于我的问题不用看明白应该可以的啦，现在应该明白了吧。。。。

[pipi1314yatou]

这么专业啊

[ekisstherain]

[Quote=引用 7 楼 haibo0321 的回复:]
判断改为 if (null == str || "".equals(str))
你可以调试跟一下程序 就会发现当回车的时候 str="" 而不是NULL
[/Quote]

你的解答正确，现在就是怎么去掉空格的问题了
谢谢你啦

[ekisstherain]

[Quote=引用 13 楼 pipi1314yatou 的回复:]
这么专业啊
[/Quote]

???