Question

How to convert a string lowercase characters to uppercase and uppercase to lowercase with Java

Answer 1

public class MyClass {
    public static String char_to_lowercase(String s, int idx) { 
        if (idx < 0 || idx > s.length()) return s;
          
        String tmp = "";
        for (int i = 0; i < s.length(); i++) {
            if (i == idx) {
                char ch = s.charAt(i);
                tmp += Character.toLowerCase(ch);
            }
            else
                tmp += s.charAt(i); 
        }
              
        return tmp;
    }
    public static String char_to_uppercase(String s, int idx) { 
       if (idx < 0 || idx > s.length()) return s;
          
        String tmp = "";
        for (int i = 0; i < s.length(); i++) {
            if (i == idx) {
                char ch = s.charAt(i);
                tmp += Character.toUpperCase(ch);
            }
            else
                tmp += s.charAt(i); 
        }
              
        return tmp;
    }
    public static String flip_characters(String s) { 
         int len = s.length(); 

         for (int i = 0; i < len; i++) { 
             if ((s.charAt(i)) >= 'A' && s.charAt(i) <= 'Z') 
                  s = char_to_lowercase(s, i);
            else {
                if ((s.charAt(i)) >= 'a' && s.charAt(i) <= 'z') 
                    s = char_to_uppercase(s, i);
            }
         } 
  
         return s;
    } 
    public static void main(String args[]) {
        String s = "jAVa pRograMMinG"; 

        s = flip_characters(s);
        
        System.out.println(s); 
    }
}
 
  
  
/*
run:
  
JavA PrOGRAmmINg
  
*/

 

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