Help scrambling a word

I'm fairly new to Java and I need help scrambling a word. I made the following but for some reason the if statement inside the do loop isn't working.

Code:

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import java.util.Random;

class scramble {
        public static void main(String[] args) {
                String word,newword;
                int rndnum;
                Random randGen = new Random();
                word = "tiger";
                newword="";
                boolean letter[] = new boolean[word.length()];
                do {
                        rndnum = randGen.nextInt(word.length());
                        if (letter[rndnum] = false) {
                                newword = newword + word.charAt(rndnum);
                                letter[rndnum] = true;
                        }
                } while (newword.length() < word.length());
                System.out.println(newword);
        }       
}

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Anyone know why? I printed the status of letter[rndnum] and it's always returning false, so I'm not sure why the if isn't working.

"letter[rndnum] = false" This line sets the array element to false and of course it's a false condition, so the code within the if is never executed

Oh I see, it should be ==...