removed duplicate constants

Author: SangeethaDivya

itext/itext.io/itext/io/util/ImageHandlerUtil.cs

@@ -48,10 +48,6 @@ public sealed class ImageHandlerUtil {
         public const String GS_ENVIRONMENT_VARIABLE_IS_NOT_SPECIFIED = "Ghostscript command is not specified. Set the "
              + GHOSTSCRIPT_ENVIRONMENT_VARIABLE + " environment variable to a CLI command that can run the Ghostscript application. See BUILDING.MD in the root of the repository for more details.";
 
-        private const String GHOSTSCRIPT_FAILED = "GhostScript failed for <filename>.";
-
-        private const String CANNOT_OPEN_OUTPUT_DIRECTORY = "Cannot open output directory for <filename>.";
-
         private const String GHOSTSCRIPT_PARAMS = " -dSAFER -dNOPAUSE -dBATCH -sDEVICE=png16m -r150 <pageNumberParam> -sOutputFile='<outputfile>' '<inputfile>'";
 
         private const String COMPARE_PARAMS = " '<image1>' '<image2>' '<difference>'";
@@ -108,14 +104,14 @@ public void RunGhostScriptImageGeneration(String pdf, String outDir, String imag
                 throw new ImageHandlerUtil.ImageHandlerExecutionException(this, GS_ENVIRONMENT_VARIABLE_IS_NOT_SPECIFIED);
             }
             if (!FileUtil.DirectoryExists(outDir)) {
-                throw new ImageHandlerUtil.ImageHandlerExecutionException(this, CANNOT_OPEN_OUTPUT_DIRECTORY.Replace("<filename>"
+                throw new ImageHandlerUtil.ImageHandlerExecutionException(this, iText.IO.Exceptions.IoExceptionMessageConstant.CANNOT_OPEN_OUTPUT_DIRECTORY.Replace("<filename>"
                     , pdf));
             }
             pageNumber = (pageNumber == null) ? "" : "-sPageList=<pagelist>".Replace("<pagelist>", pageNumber);
             String currGsParams = GHOSTSCRIPT_PARAMS.Replace("<pageNumberParam>", pageNumber).Replace("<outputfile>", 
                 outDir + image).Replace("<inputfile>", pdf);
             if (!SystemUtil.RunProcessAndWait(gsExec, currGsParams)) {
-                throw new ImageHandlerUtil.ImageHandlerExecutionException(this, GHOSTSCRIPT_FAILED.Replace("<filename>", pdf
+                throw new ImageHandlerUtil.ImageHandlerExecutionException(this, iText.IO.Exceptions.IoExceptionMessageConstant.GHOSTSCRIPT_FAILED.Replace("<filename>", pdf
                     ));
             }
         }

itext/itext.kernel/itext/kernel/pdf/PdfReader.cs

@@ -1780,7 +1780,7 @@ public virtual int Get(long offset) {
 
             public virtual int Get(long offset, byte[] bytes, int off, int len) {
                 if (buffer == null) {
-                    throw new InvalidOperationException("Already closed");
+                    throw new InvalidOperationException(iText.IO.Exceptions.IoExceptionMessageConstant.ALREADY_CLOSED);
                 }
                 if (offset >= buffer.Size()) {
                     return -1;

itext/itext.styledxmlparser/itext/styledxmlparser/exceptions/StyledXMLParserException.cs

@@ -41,9 +41,6 @@ public class StyledXMLParserException : ITextException {
         /// <summary>Message in case the font provider doesn't know about any fonts.</summary>
         public const String FontProviderContainsZeroFonts = "Font Provider contains zero fonts. At least one font shall be present";
 
-        /// <summary>The Constant UnsupportedEncodingException.</summary>
-        public const String UnsupportedEncodingException = "Unsupported encoding exception.";
-
         /// <summary>
         /// Creates a new
         /// <see cref="StyledXMLParserException"/>

itext/itext.styledxmlparser/itext/styledxmlparser/resolver/resource/UriEncodeUtil.cs

@@ -116,7 +116,7 @@ public static String Encode(String s, String enc)
             BinaryWriter charArrayWriter = new BinaryWriter(new MemoryStream());
             if (enc == null)
             {
-                throw new StyledXMLParserException(StyledXMLParserException.UnsupportedEncodingException);
+                throw new StyledXMLParserException(IO.Exceptions.IoExceptionMessageConstant.UNSUPPORTED_ENCODING_EXCEPTION);
             }
             charset = EncodingUtil.GetEncoding(enc);
             int i = 0;