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Finding length
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Join Date: Feb 2006
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Hi,
I'm creating a palindrome program. So far, I got that part. Now, I need to find out if the length of the integer (string) is less than 5 digits. If the length is less than 5, then don't proceed with the program. Please give your suggestions. Basically, what I'm doing is converting the Int to String and then finding the length. Thanks!
I tried the following:
if ( s.length() >= 5 ) {
// Proceed
}
and got this:
Exception in thread "main" java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at _uesJavaRun.main(_uesJavaRun.java:29)
Caused by: java.lang.StringIndexOutOfBoundsException: String index out of range: 4
at java.lang.String.charAt(String.java:558)
at palindrome.main(palindrome.java:26)
... 5 more
This is my code so far:
I'm creating a palindrome program. So far, I got that part. Now, I need to find out if the length of the integer (string) is less than 5 digits. If the length is less than 5, then don't proceed with the program. Please give your suggestions. Basically, what I'm doing is converting the Int to String and then finding the length. Thanks!
I tried the following:
if ( s.length() >= 5 ) {
// Proceed
}
and got this:
Exception in thread "main" java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at _uesJavaRun.main(_uesJavaRun.java:29)
Caused by: java.lang.StringIndexOutOfBoundsException: String index out of range: 4
at java.lang.String.charAt(String.java:558)
at palindrome.main(palindrome.java:26)
... 5 more
This is my code so far:
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import java.util.Scanner;
public class palindrome
{
public static void main (String args[])
{
Scanner input = new Scanner (System.in );
int number;
String len, size;
System.out.print( "Enter a 5-digit integer: " );
number = input.nextInt();
len = number + "";
// print error message if the length is less than 5 digits
System.out.println ("Your input is not a 5-digit long. Try again.");
}
}
try this
since a five digit number will be at least 10000 or -10000
probably a little quicker than converting to string and evaluating
its length as well.
Java Syntax (Toggle Plain Text)
if (Math.abs(number / 10) < 1000) { error message }
since a five digit number will be at least 10000 or -10000
probably a little quicker than converting to string and evaluating
its length as well.
Java Programmer and Sun Systems Administrator
----------------------------------------------
Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it.
--Brian Kernighan
----------------------------------------------
Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it.
--Brian Kernighan
I don't have that scanner thing. I use these two classes to handle input from the command line.
Pedantic.java
TextIO.java
[edit] sorry I didn't realise you were using integers instead of strings[/edit]
Pedantic.java
Java Syntax (Toggle Plain Text)
public class Pedantic { public static void main (String args[]) { //Scanner input = new Scanner (System.in ); String input; System.out.println("Please enter a five-digit integer"); input = TextIO.getWord(); if(input.length()>=5) { System.out.println("woot woot tis ok"); } else System.out.println ("Your input is not a 5-digit long. Try again."); } }
TextIO.java
Java Syntax (Toggle Plain Text)
/* The file defines a class TextIO, which provides a simple interface to Java's standard console input and output. This class defines several static methhods for reading and writing values of various type. This class will only work with standard, interactive applications. When it is used in such an application, System.out and System.in should not be used directly, since the TextIO class thinks it has exclusive control of System.out and System.in. (Actually, using System.out will probably not cause any problems, but don't use System.in.) To use this class in your program, simply include the compiled class file TextIO.class in the same directory with the class file for your main program. (If you are using a development environment such as CodeWarrior or Visual J++, you can include the source file, TextIO.java in your project.) You can then use all the public static methods from the TextIO class in your program. (In your programs, the names of the methods must be prefaced with "TextIO." For example, you should use the name TextIO.getln() rather than simply getln().) (This class is for use with my on-line introductory java textbook, which is available at http://math.hws.edu/eck/cs124/notes/index.html.) Written by: David Eck Department of Mathematics and Computer Science Hobart and William Smith Colleges Geneva, NY 14456 Email: eck@hws.edu WWW: http://math.hws.edu/eck/ July 16, 1998 Modified February, 2000; getChar() now skips blanks and CR's, and getAnyChar() can be used to read the next char even if it's a blank or CR. */ import java.io.*; public class TextIO { // *************************** I/O Methods ********************************* // Methods for writing the primitive types, plus type String, // to the console, with no extra spaces. // // Note that the real-number data types, float // and double, a rounded version is output that will // use at most 10 or 11 characters. If you want to // output a real number with full accuracy, use // "TextIO.put(String.valueOf(x))", for example. public static void put(int x) { put(x,0); } // Note: also handles byte and short! public static void put(long x) { put(x,0); } public static void put(double x) { put(x,0); } // Also handles float. public static void put(char x) { put(x,0); } public static void put(boolean x) { put(x,0); } public static void put(String x) { put(x,0); } // Methods for writing the primitive types, plus type String, // to the console,followed by a carriage return, with // no extra spaces. public static void putln(int x) { put(x,0); newLine(); } // Note: also handles byte and short! public static void putln(long x) { put(x,0); newLine(); } public static void putln(double x) { put(x,0); newLine(); } // Also handles float. public static void putln(char x) { put(x,0); newLine(); } public static void putln(boolean x) { put(x,0); newLine(); } public static void putln(String x) { put(x,0); newLine(); } // Methods for writing the primitive types, plus type String, // to the console, with a minimum field width of w, // and followed by a carriage return. // If output value is less than w characters, it is padded // with extra spaces in front of the value. public static void putln(int x, int w) { put(x,w); newLine(); } // Note: also handles byte and short! public static void putln(long x, int w) { put(x,w); newLine(); } public static void putln(double x, int w) { put(x,w); newLine(); } // Also handles float. public static void putln(char x, int w) { put(x,w); newLine(); } public static void putln(boolean x, int w) { put(x,w); newLine(); } public static void putln(String x, int w) { put(x,w); newLine(); } // Method for outputting a carriage return public static void putln() { newLine(); } // Methods for writing the primitive types, plus type String, // to the console, with minimum field width w. public static void put(int x, int w) { dumpString(String.valueOf(x), w); } // Note: also handles byte and short! public static void put(long x, int w) { dumpString(String.valueOf(x), w); } public static void put(double x, int w) { dumpString(realToString(x), w); } // Also handles float. public static void put(char x, int w) { dumpString(String.valueOf(x), w); } public static void put(boolean x, int w) { dumpString(String.valueOf(x), w); } public static void put(String x, int w) { dumpString(x, w); } // Methods for reading in the primitive types, plus "words" and "lines". // The "getln..." methods discard any extra input, up to and including // the next carriage return. // A "word" read by getlnWord() is any sequence of non-blank characters. // A "line" read by getlnString() or getln() is everything up to next CR; // the carriage return is not part of the returned value, but it is // read and discarded. // Note that all input methods except getAnyChar(), peek(), the ones for lines // skip past any blanks and carriage returns to find a non-blank value. // getln() can return an empty string; getChar() and getlnChar() can // return a space or a linefeed ('\n') character. // peek() allows you to look at the next character in input, without // removing it from the input stream. (Note that using this // routine might force the user to enter a line, in order to // check what the next character is.) // Acceptable boolean values are the "words": true, false, t, f, yes, // no, y, n, 0, or 1; uppercase letters are OK. // None of these can produce an error; if an error is found in input, // the user is forced to re-enter. // Available input routines are: // // getByte() getlnByte() getShort() getlnShort() // getInt() getlnInt() getLong() getlnLong() // getFloat() getlnFloat() getDouble() getlnDouble() // getChar() getlnChar() peek() getAnyChar() // getWord() getlnWord() getln() getString() getlnString() // // (getlnString is the same as getln and is onlyprovided for consistency.) public static byte getlnByte() { byte x=getByte(); emptyBuffer(); return x; } public static short getlnShort() { short x=getShort(); emptyBuffer(); return x; } public static int getlnInt() { int x=getInt(); emptyBuffer(); return x; } public static long getlnLong() { long x=getLong(); emptyBuffer(); return x; } public static float getlnFloat() { float x=getFloat(); emptyBuffer(); return x; } public static double getlnDouble() { double x=getDouble(); emptyBuffer(); return x; } public static char getlnChar() { char x=getChar(); emptyBuffer(); return x; } public static boolean getlnBoolean() { boolean x=getBoolean(); emptyBuffer(); return x; } public static String getlnWord() { String x=getWord(); emptyBuffer(); return x; } public static String getlnString() { return getln(); } // same as getln() public static String getln() { StringBuffer s = new StringBuffer(100); char ch = readChar(); while (ch != '\n') { s.append(ch); ch = readChar(); } return s.toString(); } public static byte getByte() { return (byte)readInteger(-128L,127L); } public static short getShort() { return (short)readInteger(-32768L,32767L); } public static int getInt() { return (int)readInteger((long)Integer.MIN_VALUE, (long)Integer.MAX_VALUE); } public static long getLong() { return readInteger(Long.MIN_VALUE, Long.MAX_VALUE); } public static char getAnyChar(){ return readChar(); } public static char peek() { return lookChar(); } public static char getChar() { // skip spaces & cr's, then return next char char ch = lookChar(); while (ch == ' ' || ch == '\n') { readChar(); if (ch == '\n') dumpString("? ",0); ch = lookChar(); } return readChar(); } public static float getFloat() { float x = 0.0F; while (true) { String str = readRealString(); if (str.equals("")) { errorMessage("Illegal floating point input.", "Real number in the range " + Float.MIN_VALUE + " to " + Float.MAX_VALUE); } else { Float f = null; try { f = Float.valueOf(str); } catch (NumberFormatException e) { errorMessage("Illegal floating point input.", "Real number in the range " + Float.MIN_VALUE + " to " + Float.MAX_VALUE); continue; } if (f.isInfinite()) { errorMessage("Floating point input outside of legal range.", "Real number in the range " + Float.MIN_VALUE + " to " + Float.MAX_VALUE); continue; } x = f.floatValue(); break; } } return x; } public static double getDouble() { double x = 0.0; while (true) { String str = readRealString(); if (str.equals("")) { errorMessage("Illegal floating point input", "Real number in the range " + Double.MIN_VALUE + " to " + Double.MAX_VALUE); } else { Double f = null; try { f = Double.valueOf(str); } catch (NumberFormatException e) { errorMessage("Illegal floating point input", "Real number in the range " + Double.MIN_VALUE + " to " + Double.MAX_VALUE); continue; } if (f.isInfinite()) { errorMessage("Floating point input outside of legal range.", "Real number in the range " + Double.MIN_VALUE + " to " + Double.MAX_VALUE); continue; } x = f.doubleValue(); break; } } return x; } public static String getWord() { char ch = lookChar(); while (ch == ' ' || ch == '\n') { readChar(); if (ch == '\n') dumpString("? ",0); ch = lookChar(); } StringBuffer str = new StringBuffer(50); while (ch != ' ' && ch != '\n') { str.append(readChar()); ch = lookChar(); } return str.toString(); } public static boolean getBoolean() { boolean ans = false; while (true) { String s = getWord(); if ( s.equalsIgnoreCase("true") || s.equalsIgnoreCase("t") || s.equalsIgnoreCase("yes") || s.equalsIgnoreCase("y") || s.equals("1") ) { ans = true; break; } else if ( s.equalsIgnoreCase("false") || s.equalsIgnoreCase("f") || s.equalsIgnoreCase("no") || s.equalsIgnoreCase("n") || s.equals("0") ) { ans = false; break; } else errorMessage("Illegal boolean input value.", "one of: true, false, t, f, yes, no, y, n, 0, or 1"); } return ans; } // ***************** Everything beyond this point is private ******************* // ********************** Utility routines for input/output ******************** private static InputStream in = System.in; // rename standard input stream private static PrintStream out = System.out; // rename standard output stream private static String buffer = null; // one line read from input private static int pos = 0; // position of next char in input line that has // not yet been processed private static String readRealString() { // read chars from input following syntax of real numbers StringBuffer s=new StringBuffer(50); char ch=lookChar(); while (ch == ' ' || ch == '\n') { readChar(); if (ch == '\n') dumpString("? ",0); ch = lookChar(); } if (ch == '-' || ch == '+') { s.append(readChar()); ch = lookChar(); while (ch == ' ') { readChar(); ch = lookChar(); } } while (ch >= '0' && ch <= '9') { s.append(readChar()); ch = lookChar(); } if (ch == '.') { s.append(readChar()); ch = lookChar(); while (ch >= '0' && ch <= '9') { s.append(readChar()); ch = lookChar(); } } if (ch == 'E' || ch == 'e') { s.append(readChar()); ch = lookChar(); if (ch == '-' || ch == '+') { s.append(readChar()); ch = lookChar(); } while (ch >= '0' && ch <= '9') { s.append(readChar()); ch = lookChar(); } } return s.toString(); } private static long readInteger(long min, long max) { // read long integer, limited to specified range long x=0; while (true) { StringBuffer s=new StringBuffer(34); char ch=lookChar(); while (ch == ' ' || ch == '\n') { readChar(); if (ch == '\n'); dumpString("? ",0); ch = lookChar(); } if (ch == '-' || ch == '+') { s.append(readChar()); ch = lookChar(); while (ch == ' ') { readChar(); ch = lookChar(); } } while (ch >= '0' && ch <= '9') { s.append(readChar()); ch = lookChar(); } if (s.equals("")){ errorMessage("Illegal integer input.", "Integer in the range " + min + " to " + max); } else { String str = s.toString(); try { x = Long.parseLong(str); } catch (NumberFormatException e) { errorMessage("Illegal integer input.", "Integer in the range " + min + " to " + max); continue; } if (x < min || x > max) { errorMessage("Integer input outside of legal range.", "Integer in the range " + min + " to " + max); continue; } break; } } return x; } private static String realToString(double x) { // Goal is to get a reasonable representation of x in at most // 10 characters, or 11 characters if x is negative. if (Double.isNaN(x)) return "undefined"; if (Double.isInfinite(x)) if (x < 0) return "-INF"; else return "INF"; if (Math.abs(x) <= 5000000000.0 && Math.rint(x) == x) return String.valueOf( (long)x ); String s = String.valueOf(x); if (s.length() <= 10) return s; boolean neg = false; if (x < 0) { neg = true; x = -x; s = String.valueOf(x); } if (x >= 0.00005 && x <= 50000000 && (s.indexOf('E') == -1 && s.indexOf('e') == -1)) { // trim x to 10 chars max s = round(s,10); s = trimZeros(s); } else if (x > 1) { // construct exponential form with positive exponent long power = (long)Math.floor(Math.log(x)/Math.log(10)); String exp = "E" + power; int numlength = 10 - exp.length(); x = x / Math.pow(10,power); s = String.valueOf(x); s = round(s,numlength); s = trimZeros(s); s += exp; } else { // constuct exponential form long power = (long)Math.ceil(-Math.log(x)/Math.log(10)); String exp = "E-" + power; int numlength = 10 - exp.length(); x = x * Math.pow(10,power); s = String.valueOf(x); s = round(s,numlength); s = trimZeros(s); s += exp; } if (neg) return "-" + s; else return s; } private static String trimZeros(String num) { // used by realToString if (num.indexOf('.') >= 0 && num.charAt(num.length() - 1) == '0') { int i = num.length() - 1; while (num.charAt(i) == '0') i--; if (num.charAt(i) == '.') num = num.substring(0,i); else num = num.substring(0,i+1); } return num; } private static String round(String num, int length) { // used by realToString if (num.indexOf('.') < 0) return num; if (num.length() <= length) return num; if (num.charAt(length) >= '5' && num.charAt(length) != '.') { char[] temp = new char[length+1]; int ct = length; boolean rounding = true; for (int i = length-1; i >= 0; i--) { temp[ct] = num.charAt(i); if (rounding && temp[ct] != '.') { if (temp[ct] < '9') { temp[ct]++; rounding = false; } else temp[ct] = '0'; } ct--; } if (rounding) { temp[ct] = '1'; ct--; } // ct is -1 or 0 return new String(temp,ct+1,length-ct); } else return num.substring(0,length); } private static void dumpString(String str, int w) { // output string to console for (int i=str.length(); i<w; i++) out.print(' '); for (int i=0; i<str.length(); i++) if ((int)str.charAt(i) >= 0x20 && (int)str.charAt(i) != 0x7F) // no control chars or delete out.print(str.charAt(i)); else if (str.charAt(i) == '\n' || str.charAt(i) == '\r') newLine(); } private static void errorMessage(String message, String expecting) { // inform user of error and force user to re-enter. newLine(); dumpString(" *** Error in input: " + message + "\n", 0); dumpString(" *** Expecting: " + expecting + "\n", 0); dumpString(" *** Discarding Input: ", 0); if (lookChar() == '\n') dumpString("(end-of-line)\n\n",0); else { while (lookChar() != '\n') out.print(readChar()); dumpString("\n\n",0); } dumpString("Please re-enter: ", 0); readChar(); // discard the end-of-line character } private static char lookChar() { // return next character from input if (buffer == null || pos > buffer.length()) fillBuffer(); if (pos == buffer.length()) return '\n'; return buffer.charAt(pos); } private static char readChar() { // return and discard next character from input char ch = lookChar(); pos++; return ch; } private static void newLine() { // output a CR to console out.println(); out.flush(); } private static boolean possibleLinefeedPending = false; private static void fillBuffer() { // Wait for user to type a line and press return, // and put the typed line into the buffer. StringBuffer b = new StringBuffer(); out.flush(); try { int ch = in.read(); if (ch == '\n' && possibleLinefeedPending) ch = in.read(); possibleLinefeedPending = false; while (ch != -1 && ch != '\n' && ch != '\r') { b.append((char)ch); ch = in.read(); } possibleLinefeedPending = (ch == '\r'); if (ch == -1) { System.out.println("\n*** Found an end-of-file while trying to read from standard input!"); System.out.println("*** Maybe your Java system doesn't implement standard input?"); System.out.println("*** Program will be terminated.\n"); throw new RuntimeException("End-of-file on standard input."); } } catch (IOException e) { System.out.println("Unexpected system error on input."); System.out.println("Terminating program."); System.exit(1); } buffer = b.toString(); pos = 0; } private static void emptyBuffer() { // discard the rest of the current line of input buffer = null; } } // end of class Console
[edit] sorry I didn't realise you were using integers instead of strings[/edit]
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Originally Posted by masijade
try this
Java Syntax (Toggle Plain Text)
if (Math.abs(number / 10) < 1000) { error message }
since a five digit number will be at least 10000 or -10000
probably a little quicker than converting to string and evaluating
its length as well.
Exception in thread "main" java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at _uesJavaRun.main(_uesJavaRun.java:29)
Caused by: java.lang.StringIndexOutOfBoundsException: String index out of range: 4
at java.lang.String.charAt(String.java:558)
at palindrome.main(palindrome.java:26)
... 5 more
What am I doing wrong?
Can you get this basic program to compile and execute properly?
If not you probably have your paths set up incorrectly. If this is the case check out the read_me files that came with whatever IDE you are using. Gotta Walk before you can run.
Java Syntax (Toggle Plain Text)
class Salut{ public static void main(String[] args){ String greeting = "salut monde"; System.out.println(greeting); } }
If not you probably have your paths set up incorrectly. If this is the case check out the read_me files that came with whatever IDE you are using. Gotta Walk before you can run.
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Originally Posted by iamthwee
Can you get this basic program to compile and execute properly?
Java Syntax (Toggle Plain Text)
class Salut{ public static void main(String[] args){ String greeting = "salut monde"; System.out.println(greeting); } }
If not you probably have your paths set up incorrectly. If this is the case check out the read_me files that came with whatever IDE you are using. Gotta Walk before you can run.
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Originally Posted by webmasts
Yeah, it's working. Someone gave me a tip on using the % and / to compare the length. Any example? Thanks!
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Why are you worrying about finding the length when it's still an integer? Convert it to a string. You'll have to do so sooner or later until you decide to do it some hard way:
all the code you need.
Java Syntax (Toggle Plain Text)
StringBuffer sb = new StringBuffer(string); newstring = sb.reverse(); if (string.equals(newstring) ) { //palindrome }
all the code you need.
>all the code you need.
No I don't think so. I think the purpose of his assignment is to think of a way to check if an integer is a palindrome using the modulus and division operators.
I don't think he is even allowed to convert it to strings. He is just confused as to how to ascertain how many digits there are in a given integer... and is going down the string.length() avenue because he doesn't know any better.
Here's a hint to find out how many digits are in an integer:
>keep dividing the integer by ten until it gets to zero, each time incrementing a counter.
No I don't think so. I think the purpose of his assignment is to think of a way to check if an integer is a palindrome using the modulus and division operators.
I don't think he is even allowed to convert it to strings. He is just confused as to how to ascertain how many digits there are in a given integer... and is going down the string.length() avenue because he doesn't know any better.
Here's a hint to find out how many digits are in an integer:
>keep dividing the integer by ten until it gets to zero, each time incrementing a counter.
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