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javaincrementstringbuffer

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?

Solution

  • 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.