How to replace specific characters in a String wit

问题:

Given a

String text = "RHKKA";

How to efficiently replace all 'R' with 'H', all 'H' with 'E', all 'K' with 'L' and all 'A' with 'O'?

String text would be HELLO then.

回答1:

You can create a Map of Character as key and value, then loop over character by character like so :

String text = "RHKKA";
Map<Character, Character> map = new HashMap<>();
map.put('R', 'H');
map.put('H', 'E');
map.put('K', 'L');
map.put('A', 'O');
char[] chars = text.toCharArray();
for (int i = 0; i < chars.length; i++) {
    chars[i] = map.get(chars[i]);
}
String result = String.valueOf(chars);
System.out.println(result.toString());//HELLO

---

Java8+ possible solution

Or if you are using Java8+ you can use :

String result = text.chars()
        .mapToObj(c -> String.valueOf(map.get((char) c)))
        .collect(Collectors.joining());//HELLO

---

Java9+ possible solution

Another possible solution if to use Matcher::replaceAll like so :

String text = "RHKKA";
Map<Character, Character> map = Map.of('R', 'H', 'H', 'E', 'K', 'L', 'A', 'O');
text = Pattern.compile(".").matcher(text)
        .replaceAll(c -> String.valueOf(map.get(c.group().charAt(0))));//HELLO

---

You can read more about Map.of

回答2:

There is no such function in standard Java but you can look at Apache Commons StringUtils.replaceChars which replaces group with another group in one go, effectively doing the same as Unix tr command:

StringUtils.replaceChars("RHKKA", "RHKA", "HELE") = "HELLO".

回答3:

I think your best bet is to create a new String or StringBuilder by replacing all characters in the original one with the correct ones.
Something like:

String text = "RHKKA";
StringBuilder newString = new StringBuilder(text.length());

for (int i = 0; i < text.length(); i++) {
     char newChar = text.charAt(i);
     if (text.charAt(i) == 'R')
         newChar = 'H';
     else if (text.charAt(i) == 'H')
         newChar = 'E';
     else if (text.charAt(i) == 'K')
         newChar = 'L';
     else if (text.charAt(i) == 'A')
         newChar = 'O';
     newString.append(newChar);
}
System.out.println(newString); //prints HELLO

回答4:

Here is an alternative way based on the character replacement:

String text = "RHKKA";

String before = "RHKA";       // before mapping
String after  = "HELO";       // after mapping

String output = Arrays.stream(text.split(""))                   // Split by characters
    .map(i -> String.valueOf(after.charAt(before.indexOf(i))))  // Replace each letter
    .collect(Collectors.joining(""));                           // Collect to String

System.out.println(output);   // HELLO

By the way, I am sure you meant to replace A with O.. not E as you have in the description.