How to Shuffle char From Array of Strings?

> i am trying to make game guess the word but I cant shuffle char from
> array of string

 String names_ofcolor[] = {"red", "green", "blue"};

 int random = (int) (Math.random() * names_ofcolor.length);

    for (int j = 0; j < names_ofcolor[random].length(); j++) {


         Button btn = new Button(this);

        btn.setId(j);
        btn.setBackgroundColor(Color.WHITE);
        btn.setTextSize(16);
        linearlayout.addView(btn);
        btn.setText("" + names_ofcolor[random].charAt(j));

    }

Create a List of indices from 0 to names_ofcolor[random].length() - 1 and shuffle it using Collections::shuffle. Then, you can use the shuffled indices to set the label of the button.

String names_ofcolor[] = { "red", "green", "blue" };

int random = (int) (Math.random() * names_ofcolor.length);
List<Integer> indices = new ArrayList<Integer>();
for (int i = 0; i < names_ofcolor[random].length(); i++) {
	indices.add(i);
}
Collections.shuffle(indices);
for (int j = 0; j < names_ofcolor[random].length(); j++) {    
	Button btn = new Button(this);    
	btn.setId(j);
	btn.setBackgroundColor(Color.WHITE);
	btn.setTextSize(16);
	linearlayout.addView(btn);
	btn.setText("" + names_ofcolor[random].charAt(indices.get(j)));
}

A quick demo:

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Main {
	public static void main(String[] args) {
		String names_ofcolor[] = { "red", "green", "blue" };

		int random = (int) (Math.random() * names_ofcolor.length);
		List<Integer> indices = new ArrayList<Integer>();
		for (int i = 0; i < names_ofcolor[random].length(); i++) {
			indices.add(i);
		}
		Collections.shuffle(indices);
		for (int j = 0; j < names_ofcolor[random].length(); j++) {
			String label = "" + names_ofcolor[random].charAt(indices.get(j));
			System.out.print(label);
		}
	}
}

A sample run:

regne

Another sample run:

erd

Another sample run:

elbu