Java Insert randomly into String

Question

How do i insert a random variable into a string? I created a a variable that gets me a random position in the string that i want to put a char in, but I do not know how to use that random value in order to put that char in that certain position. Here is the code I did to get the random variable-

r=0+Math.random()*intTop;

I know this gives me a double, which is why i will cast it later. intTop is the length of the string that i will put the char in. I did this substring and it does not work,-

stringTop=stringTop.substring((int)r,lastBot);

lastBot is the char variable that i want to insert at position r of the string. Please help I am truly stuck.

stringTop.substring(0, r) + lastBot + stringTop.substring(r) ? — Patashu
– Patashu, Commented Mar 8, 2013 at 1:05

aseldawy · Accepted Answer · 2013-03-08 01:08:51Z

3

Java Strings are immutable which means you cannot modify a String in place. Rather, you should create a new string. You can accomplish this by splitting the original string into two parts and inserting the new character in between. Something like this,

stringTop.substring(0, r) + lastBot + stringTop.substring(r);

Hope this helps you

answered Mar 8, 2013 at 1:08

aseldawy

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3 Comments

user2146662 Over a year ago

For the last part, would I add Top.substring(lengthofstring +1) instead of Top.substring(r)? r is the random part of the string that the character gets added to.

James Over a year ago

@user2146662 - what aseldawy wrote is correct. stringTop.substring(r) returns the substring starting at position r and going to the end of the string. Well, correct assuming you want to insert a character (make the string one character longer). If you wanted to replace the character, you'd say r + 1 instead of r, instead.

user2146662 Over a year ago

I did this - stringTop=stringTop + stringTop.substring(0,(int) r) + lastBot + stringTop.substring((int)r+ 1); and it gives me an error D:

Evgeniy Dorofeev · Accepted Answer · 2013-03-08 02:24:28Z

0

to put a char in a certain position of a string

    char[] chars = str.toCharArray();
    chars[r] = c;
    str = new String(chars);

or

        StringBuilder sb = new StringBuilder(str);
    sb.setCharAt(r, c);
    str = sb.toString();

edited Mar 8, 2013 at 2:24

answered Mar 8, 2013 at 1:47

Evgeniy Dorofeev

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2 Comments

user2146662 Over a year ago

Do i need to import anything for this?

Evgeniy Dorofeev Over a year ago

nothing, all is in java.lang. r - is your random index, str - string, c - character to set

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