drjava - Compile error: Incompatible operand types java.lang.String and char -

import java.io.*; import hsa.console; import java.awt.*;       public static void main(string[] args) throws ioexception {         c = new console();          string sentence;         string encrypt = "";         string vowels = "aeiouaeiou";         final string punctaution = ".,;?!\"\\/\' -";         stringbuffer removepunctation = new stringbuffer();         stringbuffer thirdletters = new stringbuffer();          char tempchar;          //open output file          printwriter output;         output = new printwriter(new filewriter("output.txt"));          c.println("please enter sentence encrypt");         sentence = c.readline();           (int = 0; < sentence.length(); i++) {             tempchar = sentence.charat(i);              if (punctaution.indexof(tempchar) == -1) {                 encrypt = encrypt + tempchar;             }         }         if (encrypt == 'a') {             sentence.replace('a', '!');         } else if (encrypt == 'i') {             sentence.replace('i', '#');         } else if (encrypt == 'e') {             sentence.replace('e', '@');         } else if (encrypt == 'o') {             sentence.replace('o', '$');         } else if (encrypt == 'u') {             sentence.replace('u', '%');         }         c.println(encrypt.tostring().touppercase());          output.println(encrypt.tostring().touppercase());     } 

i'm trying remove punctuation , spaces, , change vowels aeiou !@#$%, i'm getting error. trying output vowels replaced sentence @ bottom , reverse them.

to test strings equality, use string.equals(). example, "a".equals(encrypt) tests if string encrypt capital letter a.

notice that, above, preferable put constant string first (instead of encrypt.equals("a")) avoid possibility of null pointer exception.

if want case-insensitive matching, there's string.equalsignorecase().

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and regarding task @ hand (e.g., remove/replace occurrences of something), might consider using regular expressions instead.

for example, replace capital letter ! use like:

encrypt.replaceall("a", "!") 

or, if you'll using same regular expression pattern on , on again or want flexibility make case-insensitive patterns, then:

pattern = pattern.compile("a", pattern.case_insensitive); ... a.matcher(encrypt).replaceall("!");