CODEWITHSUNDEEP
javaincrementstringbuffer
Ajay Lamba
Ajay Lamba

Reputation: 13

Can somebody explain below code related to StringBuffer in java?

StringBuffer sb=new StringBuffer("A");

Now to increment the letter A I have written below code-

if (sb.charAt(0)=='A') {
    sb.setCharAt(0, 'B');
} else {
    sb.setCharAt(0, 'C');
}

But somewhere I read that this can be done with below code as well (and it worked!)

sb.setCharAt(0, (char)(sb.charAt(0) + 1));

Can somebody explain the above code?

Upvotes: 0

Views: 261

Answers (4)

Pshemo
Pshemo

Reputation: 124275

When you do char + int char is interpreted as int which represents index of used char in Unicode Table.

So when you execute sb.charAt(0) + 1 it is same as 'A' + 1 and is evaluated as 65 + 1 which equals 66 (and character indexed with that value in Unicode Table is B).

Now since setCharAt expects as second argument char you must (cast) that int to char which gives you back 'B' and sb.setCharAt(0, ..) simply sets up that character at position 0 of in your StringBuffer.

Upvotes: 1

Vucko
Vucko

Reputation: 7479

This works because of the implicit conversion. As you probably know, every character has it's ASCII number representation. For example, letter 'A' is number 64. When you write

sb.setCharAt(0, (char) (sb.charAt(0) + 1));

It automatically converts (implicitly) the character to integer because it needs to add 1 to it. So your result becomes 64+1 = 65. After this, you explicitly call a typecast operator (char) to convert the integer number of 65 to char it represents, and it's B.

Upvotes: 0

Oliver Dain
Oliver Dain

Reputation: 9963

sb.charAt(0) is going to retrieve the first character. So sb.charAt(0) + 1 will add 1 to the first character (turning an A into a B, a B into a C, etc.). So, lets suppose the first character is an A. Then sb.charAt(0) + 1 == 'B' so your method is sb.setCharAt(0, 'B'), etc.

Upvotes: 0

Elliott Frisch
Elliott Frisch

Reputation: 201507

If the first character is an A change the first character to a B. Otherwise, set the first character to a C. Your modified version

sb.setCharAt(0, (char) (sb.charAt(0) + 1));

would only work the same way for input of A and B respectively (because it increments the first character in the StringBuffer).

Upvotes: 0

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