agusbrand

final TextView firstTextView = (TextView) findViewById(R.id.textView);
final Button firstButton = (Button) findViewById(R.id.firstButton);

// ACA escribir View.OnClickListener(){   Y APRETAR CTRL+i
        firstButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                firstTextView.setText("You clicked!");
            }
        });

agusbrand

myButton.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {
        SimpleDateFormat formatter = new SimpleDateFormat("h:mm:ss a");
        String strWhen = formatter.format(new Date());               
        TextView myTextview = (TextView) 
            findViewById(R.id.TextViewToShow);
        myTextview.setText("Clicked at " +  strWhen);
    }
});