replacing particular characters in a string with...

[Justin Fox]

ok say you have the string:

"((R))(SR)()()S"

I need to replace all the "S" and "R"'s with "()"

how do I go about doing this?

with out using String.replaceAll

cause I just couldn't get that darn method to work


Thanks,
Justin

[marc weber]

Originally posted by Justin Fox:
...with out using String.replaceAll

cause I just couldn't get that darn method to work...

I think it would be easier to figure out how that darn method works before trying to write your own algorithm. What have you tried? And what seems to be the problem?

[Keith Lynn]

Keep in mind that Strings are immutable, and calling methods on them won't change them.

[Justin Fox]

nevermind, lol

I used String.replaceAll(substring a, string b);

I have two recursive methods that needed to call it,

and only had it in one...

so say i had this string at current outcome..

(S)RRR())S)

the actual outcome was (())RRR())())
because i only had the converting method in the S() function..


I figured it out...

here is the code:

    
 
public class Exp{
 
/*Two private variables, one to hold the
**original length of the expression you 
**wanted to find, and the other to count
**the different expressions.
*/
 
private int original;
private int count;
 
public Exp(int length)
{original = length;
count = 0;
S("S", length);

}
 
 
public void S(String a, int L)
   { 
      
if(L == 0)
{
String A = withoutSR(a);
if(A.length() == original)
{
Print(a);

}
}

        else
    
      {
      RULE1(a, L);
      RULE2(a, L);
}
  

 
   }
 
 
public void R(String a, int L)
{
if(L == 0)
{
String A = withoutSR(a);
if(A.length() == original)
Print(a);

}
else
{
      RULE3(a, L);
      RULE4(a, L);
}
}
 
// S ---> SR
public void RULE1(String a, int L)
   {
      String two = a.replaceFirst("S","SR");
 
      S(two, L-1);
   }
 
// S ---> R
public void RULE2(String a, int L)
   {
      String one = a.replaceFirst("S","R");
      R(one, L-1);
   }
 
// R ---> (S)
public void RULE3(String a, int L)
   {
      String one = a.replaceFirst("R","(S)");
      S(one, L-1);
   }
 
// R ---> ()
public void RULE4(String a, int L)
   {
      String one = a.replaceFirst("R","()");
      R(one, L-1);
   }
 
/*
**method use to find what the leftmost Nonterminal
**is..
*/
public String leftmost(String a)
{
if(a.lastIndexOf("S") < a.lastIndexOf("R"))
{
return "S";
}
else
return "R";
}
 
public void Print(String a)
{
System.out.println(a);
count++;
}
 
/*
**Method used to convert all remaining
**NonTerminals to "()"
*/
 
public String withoutSR(String a)
{
int count = 0;
 
 
 
boolean first = true;
 
while(count < 2)
{
if(first)
{a = a.replaceAll("R","()"); first = false;}
else
a = a.replaceAll("R","()");

count ++;
}
return a;
 
}
 
/*
**Just returns the global variable
**count
*/
public int getCount()
{return count;}

 
}
 

    
 
/* *********
 
Justin Fox 
COSC 3320
Dr. Koh
Program 1
 
********* */
 
public class Running{
 
public static void main(String[]args)
{
Thread t = new Thread();
 
//**********************************************************************************
 
System.out.println("Getting all possible expressions for length 8...");
try{
t.sleep(5000);}
catch(InterruptedException e){}
 
Exp a = new Exp(8);
 
System.out.println("There were "+a.getCount()+" expressions for length 8");
 
//**********************************************************************************
//**********************************************************************************
 
System.out.println("Getting all possible expressions for length 10...");
try{
t.sleep(5000);}
catch(InterruptedException e){}
 
Exp b = new Exp(10);
 
System.out.println("There were "+b.getCount()+" expressions for length 10");
 
//**********************************************************************************
//**********************************************************************************
 
System.out.println("Getting all possible expressions for length 12...");
try{
t.sleep(5000);}
catch(InterruptedException e){}
 
Exp c = new Exp(12);
 
System.out.println("There were "+c.getCount()+" expressions for length 12");
 
//**********************************************************************************
//**********************************************************************************
 
System.out.println("Getting all possible expressions for length 14...");
try{
t.sleep(5000);}
catch(InterruptedException e){}
 
Exp d = new Exp(14);
 
System.out.println("There were "+d.getCount()+" expressions for length 14");
 
//**********************************************************************************

}
 
}

Justin
[ September 23, 2006: Message edited by: Justin Fox ]

[Justin Fox]

ok i modified the above Exp class to print to a file, but
for some reason i keep getting this error:

    
 
C:\Documents and Settings\lamar\Desktop>java Running
Getting all possible expressions for length 8...
()()()()
Exception in thread "main" java.lang.NullPointerException
        at Exp.Print(Exp.java:122)
        at Exp.R(Exp.java:63)
        at Exp.RULE4(Exp.java:101)
        at Exp.R(Exp.java:71)
        at Exp.RULE4(Exp.java:101)
        at Exp.R(Exp.java:71)
        at Exp.RULE4(Exp.java:101)
        at Exp.R(Exp.java:71)
        at Exp.RULE4(Exp.java:101)
        at Exp.R(Exp.java:71)
        at Exp.RULE2(Exp.java:87)
        at Exp.S(Exp.java:48)
        at Exp.RULE1(Exp.java:80)
        at Exp.S(Exp.java:47)
        at Exp.RULE1(Exp.java:80)
        at Exp.S(Exp.java:47)
        at Exp.RULE1(Exp.java:80)
        at Exp.S(Exp.java:47)
        at Exp.<init>(Exp.java:21)
        at Running.main(Running.java:23)

here is the modified code...

    
 
import java.io.*;
 

public class Exp{
 
/*Two private variables, one to hold the
**original length of the expression you
**wanted to find, and the other to count
**the different expressions.
*/
 
private int original;
private int count;
PrintWriter writer = null;
 
public Exp(int length)
{ 
 
original = length;
count = 0;
S("S", length);
 
try
{
writer = new PrintWriter(new BufferedWriter(new FileWriter("newfile.txt")));
}
catch(IOException e){}
 
}
 

public void S(String a, int L)
{
 
if(L == 0)
{
String A = withoutSR(a);
if(A.length() == original)
{
Print(A);
 
}
}
 
else
 
{
RULE1(a, L);
RULE2(a, L);
}
 

 
}
 

public void R(String a, int L)
{
if(L == 0)
{
String A = withoutSR(a);
if(A.length() == original)
{
Print(A);
 
}
 
}
else
{
RULE3(a, L);
RULE4(a, L);
}
}
 
// S ---> SR
public void RULE1(String a, int L)
{
String two = a.replaceFirst("S","SR");
 
S(two, L-1);
}
 
// S ---> R
public void RULE2(String a, int L)
{
String one = a.replaceFirst("S","R");
R(one, L-1);
}
 
// R ---> (S)
public void RULE3(String a, int L)
{
String one = a.replaceFirst("R","(S)");
S(one, L-1);
}
 
// R ---> ()
public void RULE4(String a, int L)
{
String one = a.replaceFirst("R","()");
R(one, L-1);
}
 
/*
**method use to find what the leftmost Nonterminal
**is..
*/
public String leftmost(String a)
{
if(a.lastIndexOf("S") < a.lastIndexOf("R"))
{
return "S";
}
else
return "R";
}
 
public void Print(String a)
{
System.out.println(a);
count++;
//******************************************
//******************************************
     writer.println(a);
//******************************************
//******************************************
}
 
/*
**Method used to convert all remaining
**NonTerminals to "()"
*/
 
public String withoutSR(String a)
{
int count = 0;
 

 
boolean first = true;
 
while(count < 2)
{
if(first)
{a = a.replaceAll("R","()"); first = false;}
else
a = a.replaceAll("R","()");
 
count ++;
}
return a;
 
}
 
/*
**Just returns the global variable
**count
*/
public int getCount()
{return count;}
 

}
 

 

Please help me,

Justin

[Keith Lynn]

It's possible that an exception occurred where you created the PrintWriter.

If you put an SOP in the catch block, it may tell you what the problem is.

try
{
writer = new PrintWriter(new BufferedWriter(new FileWriter("newfile.txt")));
}
catch(IOException e){}
 
}

[Jody Brown]

On a more general note, it is a very bad practice to just swallow exceptions in this manner. Never ever do it or debugging the sort of errors you are seeing will be a serious headache. A System.out.println should be used at the very least, but preferably a e.printStackTrace() in the absence of a more complete logging framework.

[Garrett Rowe]

In the constructor for your Exp class you call S(String, int) before you instantiate your PrintWriter. At some point either the S() method or one of the RULE_X_() methods calls the PRINT() method and that tries to call a println() with the null PrintWriter.

[Justin Fox]

ok i realize i instatiated a null print writer...

but in the constructor i made it a non-null value..

so i shouldn't have a prob. using it... right?

i mean, this wasn't a part of the assignment, i just hate using

linux to make a script file...

so i was gonna output the "output" to a file and just print that up

Justin

[Garrett Rowe]

Originally posted by Justin Fox:
ok i realize i instatiated a null print writer...

but in the constructor i made it a non-null value..

so i shouldn't have a prob. using it... right?

The only problem is you're trying to use it before you instantiate it. Just try moving the creation of the PrintWriter to before you call the S() method.
[ September 26, 2006: Message edited by: Garrett Rowe ]

[Justin Fox]

lol geez, i cant believe i didn't catch that...

thanks,


Justin