problem with activity crashing when a function is called

this is my first time on this forum, so forgive me if my question seems odd. I'll try to be as thorough as possible. I am creating a translation program. this program has a menu activity, translate activity, addword activity. The three activities are linked together via intents and they are added in the manifest file. In the translate activity I want to create a method for translating. After I press the translate button, the program crashes.

public class VertaalActivity extends Activity {
private Button vertaal;
private Button terug;
private EditText ET_NL;
private EditText ET_EN;
private ArrayList<String>nlWoorden = new ArrayList<String>();
private ArrayList<String>enWoorden = new ArrayList<String>();

public void Vertaal(){

    String woord = ET_NL.getText().toString();

        if(nlWoorden.contains(woord)){
            int i = nlWoorden.in开发者_如何学编程dexOf(woord);
            ET_EN.setText(enWoorden.get(i));
        }else{
            ET_EN.setText("Woord niet gevonden");
        }

}

public void ArrayVullen(){
    nlWoorden.add("auto");
    nlWoorden.add("bord");
    nlWoorden.add("trein");
    nlWoorden.add("spel");
    nlWoorden.add("scherm");
    nlWoorden.add("toetsenbord");
    nlWoorden.add("foto");
    enWoorden.add("car");
    enWoorden.add("plate");
    enWoorden.add("train");
    enWoorden.add("game");
    enWoorden.add("screen");
    enWoorden.add("keyboard");
    enWoorden.add("picture");
}

public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    setContentView(R.layout.vertalerlayout);
    terug = (Button)findViewById(R.id.terug);
    vertaal = (Button)findViewById(R.id.vertalen);

    ArrayVullen();

    vertaal.setOnClickListener(new OnClickListener() {

        public void onClick(View v) {
            Vertaal();

            /*
             * Tested the toast and the toast shows the text 
             * 
            Context context = getApplicationContext();
            CharSequence text = "Hello toast!";
            int duration = Toast.LENGTH_SHORT;

            Toast toast = Toast.makeText(context, text, duration);
            toast.show();
            */
        }

    });

    terug.setOnClickListener(new OnClickListener() {

        public void onClick(View v) {
            Intent intent = new Intent(VertaalActivity.this,MenuActivity.class);
            startActivity(intent);

        }
    });

}

}

I can't see that you get the EditTexts from your XML (like you do with the buttons). Before using ET_NL you need to do something like this:

ET_NL = (EditText)findViewById(R.id.etnl); // Or whatever id you've declared in your layout XML

Same thing goes for the ET_EN variable. Otherwise the will be null in your Vertaal() method, causing the app to crash.

Try this code before using the editText field

ET_NL= (EditText)findViewById(R.id.edittext1);
ET_EN = (EditText)findViewById(R.id.edittext2);