gistfile1.java

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!");
            }
        });