TextView myText;
        String appName;
        String helloWord;
        String txt;
        myText = findViewById (R.id.mytext);
         appName = getResources().getString(R.string.app_name);
         helloWord = getResources().getString(R.string.helloWord);
         txt = myText.getText().toString();
          public void changeText(View v){
                if (txt.equals(helloWord)){
                    myText.setText(appName);
               }else if(txt.equals(appName)){
                    myText.setText(helloWord);
                }
            }

public void changeText(View v){
    txt = myText.getText().toString();
    if (txt.equals(helloWord)){
        myText.setText(appName);
    }else if(txt.equals(appName)){
        myText.setText(helloWord);
    }
}