Help scrambling a word

[MountainDew7]

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.

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);
	}	
}

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.

[ComputerJy]

"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

[MountainDew7]

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