Reverse each individual word of "Hello World" string with Java

Know your libraries ;-)

import org.apache.commons.lang.StringUtils;

String reverseWords(String sentence) {
    return StringUtils.reverseDelimited(StringUtils.reverse(sentence), ' ');
}

This should do the trick. This will iterate through each word in the source string, reverse it using StringBuilder's built-in reverse() method, and output the reversed word.

String source = "Hello World";

for (String part : source.split(" ")) {
    System.out.print(new StringBuilder(part).reverse().toString());
    System.out.print(" ");
}

Output:

olleH dlroW 

Notes: Commenters have correctly pointed out a few things that I thought I should mention here. This example will append an extra space to the end of the result. It also assumes your words are separated by a single space each and your sentence contains no punctuation.