CODEWITHSUNDEEP
javastring
Daniel Horowitz
Daniel Horowitz

Reputation: 33

String Manipulation java

So I have used this site a good deal, but I can't find an answer... How can I manipulate specific chars/strings from a larger string. I'm trying to use string.substring(pos,amount) but when I try and use it in loops I get a string Index Error. for instance- How could I remove 'e' at [4] from string "abcdefg" or just capitalize "cde"? Sorry for lack of formal code in my question, it's mainly a conceptual thing. Thank you.

Thanks for the suggestions I was trying to answer this question: Write a program that takes as input a string of only letters and displays the string with every third letter capitalized starting with the second letter, and all other letters lower-case.

With this code:

public class Test {
    public static void main(String[] arguments){
        Scanner fish = new Scanner(System.in);      
        String a = fish.nextLine();
        int len=a.length();
        for (int i = 1; i < len; i += 3){
            String z = a.substring(i, 1);
            String q = a.substring(i + 1);
            a = z.toUpperCase() + q;
        }
        System.out.println(a);
    }
}

Upvotes: 3

Views: 14881

Answers (5)

Penfold
Penfold

Reputation: 619

How could I remove 'e' at [4] from string "abcdefg"

As Ameya already said, if you're dealing with String objects then you can't really "remove" the e, because the String is fixed. What you have to do instead is build a new String object containing all the bits except the e:

String input = "abcdefg";
String output = input.substring(0, 4) + input.substring(5);
//                     "abcd"         +       "fg"

or just capitalize "cde"?

Again, you can take the bit before, add the upper case of "cde", and then add the rest:

String output = input.substring(0, 2) + input.substring(2, 5).toUpperCase()
                + input.substring(5);
//            = "ab" + "CDE" + "fg"

Write a program that takes as input a string of only letters and displays the string with every third letter capitalized starting with the second letter, and all other letters lower-case.

In this case you need to loop over the characters, so it's better to use a StringBuilder rather than adding the Strings together (for performance reasons). Here's an example of adding each character one by one, and for every third character converting it to upper case:

StringBuilder sb = new StringBuilder();
for (int i=0; i<input.length(); i++)
{
    char c = input.charAt(i);
    if (i%3 == 1) {
        c = Character.toUpperCase(c);  // every third character upper case
    }
    else {
        c = Character.toLowerCase(c);
    }
    sb.append(c);
}
String output = sb.toString(); // aBcdEfg

Upvotes: 0

user1267905
user1267905

Reputation:

If you know what you want to remove, say the letter "e", but you do not where it is in the string, you can use

stringName.indexOf("e");

It will return an integer of the index of the first occurrence of the string "e" within stringName. You will then have to create a new string that takes in substrings of your original string. You will have to specify the beginning and end indexes for your substrings based on the the returned integer from indexOf().

If you are using indexOf() to find a string that is longer than one character, for example indexOf("ef"), you will also need to take into account the length of this string.

Upvotes: 0

Jon Egeland
Jon Egeland

Reputation: 12623

replaceAll() could be a good option here, as per the Java API:

Replaces each substring of this string that matches the given regular expression with the given replacement.

This seems to do what you want, since you could do something like:

str.replace('e', ''); // remove 'e' from the string, or
str.replaceAll("cde", "CDE");

The problem most people have with replaceAll() is that the first parameter is not a literal String, it is regex that gets interpreted and used as a pattern to be matched against.

This is just a quick example, but using replace() and replaceAll() effectively does what you want. Granted it isn't by any means the most efficient or easiest to write.

Upvotes: 0

Ameya
Ameya

Reputation: 627

String itself is an immutable class, hence you cannot make modifications to it. When you make modifications a new object is returned back... But that is not always the best way (in terms of performance) to manipulate Strings especially when you have a large String.

Java has some other classes like StringBuffer and StringBuilder which exposes many more String manipulation operations. Following is a snippet :

`public String manipulateStr(String sourceStr) {
    StringBuffer sb = new StringBuffer(sourceStr);
    sb.delete(5,7); // Delete characters between index 5-7
    sb.insert(10, "<inserted str>"); // Insert a new String
    return sb.toString();
}`

Hope the above helps.

Upvotes: 4

corsiKa
corsiKa

Reputation: 82599

There is no easy way to do what you're looking for, unfortunately. Substring is not meant for replacements. For example, some languages allow you to do this:

str.substring(2,3).toUpperCase();

Java doesn't work that way. If you're looking for things like that, you're going to be best off writing a small function library that takes strings and coordinates and does the work manually. It's not baked into the String class. Look at what all is already baked into the String class! It doesn't need more functionality that only a small subset of users would use.

Upvotes: 0

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