Trying to make array element appear only once

So i'm trying to do this : when you click the image the text in the center changes to a random element from the array but i want every element that appears once to not appear again... I tried doing it like this but it didn't work please help me here!!

package com.example.bibiwars.skills;


import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;


import java.util.Random;


public class MainActivity extends ActionBarActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


            ImageView img = (ImageView) findViewById(R.id.logo);
            img.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            //ToastMessage to test the click ::::::
            Toast.makeText(MainActivity.this, "Clicked!!",Toast.LENGTH_SHORT).show();


            TextView text = (TextView) findViewById(R.id.text);
            String[] Array = {"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"};
            int rnd = new Random().nextInt(Array.length);
            while (Array[rnd].equals("0"))
               {rnd = new Random().nextInt(Array.length);}
            text.setText(Array[rnd]);
            Array[rnd] = "0";
        }

    });
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}



}