Strings are immutable in Java, meaning their values cannot be changed once they are created. To efficiently manipulate strings, it is recommended to convert them to StringBuilder or StringBuffer objects. StringBuilder is preferable for its speed, while StringBuffer is thread-safe.
Here's an example of converting a string to a StringBuilder:
String input = "abcd";
StringBuilder sb = new StringBuilder(input);
Appending a value to the StringBuilder can be done using the append() method:
sb.append("zz")
To check the resulting string, you can convert the StringBuilder back to a string using toString() and compare it:
assert sb.toString().equals("abcdezz");
You can also retrieve the index location of a specific substring within the StringBuilder using the indexOf() method:
int index = sb.indexOf("zz");
assert index == 5;
If you need to replace a portion of the string with another value, you can use the replace() method:
sb.replace(1, 4, "foo");
assert sb.toString().equals("afooezz");
To reverse the string in the StringBuilder, you can use the reverse() method:
sb.reverse();
assert sb.toString().equals("zzeoofa");
Removing a substring from the StringBuilder can be achieved using the delete() method:
sb.delete(3, 6);
assert sb.toString().equals("zzea");
Alternatively, you can delete a specific character at a given index using deleteCharAt():
sb.deleteCharAt(1);
assert sb.toString().equals("zea");
To access a character at a specific index within the StringBuilder, you can use charAt():
char c = sb.charAt(1);
If you wish to modify a character at a specific index, you can use setCharAt():
sb.setCharAt(1, 'z');
You can obtain the ASCII value of a character by using the charAt() method and casting it to an int:
int asciiA = sb.charAt(0);
assert asciiA == 97;
int asciiA = 'A';
assert asciiA == 65;
Conversely, you can convert an ASCII value back to a character using a cast:
char c = (char) asciiA;
assert c == 'a';
int asciiZ = 'Z';
assert asciiZ == 90;