How to make alternate characters in a string to uppercase?

Question

I wrote the following code but similar characters are always in the same case. What's wrong in this code and How can this problem be solved??

private void genBTActionPerformed(java.awt.event.ActionEvent evt) {                                      
    String str = new String(strTF.getText());
    int n = str.length();
    char ch;
    int i;
    for(i = 0; i < n; i++) {
        if(i % 2 == 0) {
            ch = Character.toLowerCase(str.charAt(i));
            str = str.replace(str.charAt(i), ch);
        } else {
            ch = Character.toUpperCase(str.charAt(i));
            str = str.replace(str.charAt(i), ch);
        }
    }
    jumTF.setText(str);
}

`replace(oldChar, newChar)` returns a new string resulting from replacing all occurrences of oldChar in this string with newChar. What you want is to [replace a character at a specific location](http://stackoverflow.com/questions/6952363/java-replace-a-character-at-a-specific-index-in-a-string). — Reti43, Jan 28 '15 at 13:24
You should work out things like this in a command line app. before worrying about how to get them to work in a GUI. And on that note, 'changing case in a string' has nothing to do with either Swing or your IDE. — Andrew Thompson, Jan 28 '15 at 13:32

score 6 · Answer 1 · answered Jan 28 '15 at 13:26

Unlike what its name says, .replace() replaces characters/CharSequences in the whole input. The difference with .replaceAll() is that it takes literals as arguments and not regexes/regex replacements strings (and that it has an overload taking two chars as arguments). That is the second worst misnamed method of the String class after matches().

Moreover you create a new String on each character you replace, so you have n+1 strings for a n character long string. Do it like this instead:

final char[] chars = str.toCharArray();

final int len = chars.length;

char c;

for (int i = 0; i < len; i++) {
    c = chars[i];

    chars[i] = i % 2 == 0
        ? Character.toLowerCase(c)
        : Character.toUpperCase(c);
}

jumTF.setText(new String(chars));

score 0 · Accepted Answer · answered Jan 28 '15 at 13:56

In your program you were using replace() which replaces characters/CharSequences in the whole input what you need to do is

Put the string into an array.
Iterate over said array.

convert that array back into string

private void genBTActionPerformed(java.awt.event.ActionEvent evt) {

String str = new String(strTF.getText());
char [] chr= str.toCharArray();
int n = chr.length;
char ch;
int i;
for(i = 0; i < n; i++) {
    if(i % 2 == 0) {
        ch = Character.toLowerCase(chr[i]);
       chr[i]=ch;
    } else {
        ch = Character.toUpperCase(chr[i]);
     chr[i]=ch;
    }
}
jumTF.setText(new String(chr)); }

hope this will help you :)

score 0 · Answer 3 · answered Jan 28 '15 at 14:19

Since String are immutable in java , you can use StringBuilder or StringBuffer to solve this problem

StringBuilder str=new StringBuilder(inputString);

You can use your own logic just with slight change instead of using

str = str.replace(str.charAt(i), ch);//since  it replaces in whole string

Use

str.setCharAt(i,ch);

So your final Program looks like this :

for(i = 0; i < n; i++) {
        if(i % 2 == 0) {
            ch = Character.toLowerCase(str.charAt(i));
            str.setCharAt(i,ch);
        } else {
            ch = Character.toUpperCase(str.charAt(i));
            str.setCharAt(i,ch);
        }
    }

Suppose InputString is : stackoverflow then output is : sTaCkOvErFlOw

How to make alternate characters in a string to uppercase?

3 Answers3