title: Deleting and shrinking an ArrayList
body: <p>I'm new at Android and today I felt really motivated, so I started writing an app.</p>
  
  <p>But now I'm stuck... I have an ArrayList with Strings in it. With a random number generator I get a String from this list. 
  What I really want to do is avoiding repeating the Strings. I want to see an element only once.</p>
  
  <p>Can you guys please help me?</p>
  
  <p>Here is my MainActivity:</p>
  
  <pre><code>public class MainActivity extends AppCompatActivity {
  
  private TextView welcomeText;
  private TextView pokemons;
  private TextView whatToDo;
  private Button yesButton;
  private Button noButton;
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
  
      final String[] pokemonok = {
              "Pikachu",
              "Charizard",
              "Bulbasaur",
              "Charmander",
              "Squirtle",
              "Caterpie",
              "Metapod",
              "Weedle",
              "Rattata",
              "Onix"
      };
  
      final List&lt;String&gt; list = new ArrayList&lt;String&gt;(pokemonok.length);
      for (String s : pokemonok) {
          list.add(s);
      }
  
      welcomeText = (TextView) findViewById(R.id.welcomeText);
      pokemons = (TextView) findViewById(R.id.pokemons);
      whatToDo = (TextView) findViewById(R.id.whatToDo);
      //EditText answerText = (EditText) findViewById(R.id.answerText);
      yesButton = (Button) findViewById(R.id.yesButton);
      noButton = (Button) findViewById(R.id.noButton);
  
      final String[] def = {"[ " + list.get(0) + " ]"};
      pokemons.setText(def[0]);
  
      View.OnClickListener igen = new View.OnClickListener() {
          @Override
          public void onClick(View view) {
  
              Random r = new Random();
              int szam = r.nextInt(pokemonok.length);
  
              pokemons.setText(def[0] + "[ " + list.get(szam) + " ]");
              def[0] = def[0] + "[ " + list.get(szam) + " ]";
  
          }
      };
  
      yesButton.setOnClickListener(igen);
  
     }
  }
  </code></pre>