Button button = (Button)findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Toast.makeText(this, "Button clicked", Toast.LENGTH_LONG).show();
    }
});

Button button = (Button)findViewById(R.id.button);
button.setOnClickListener(v -> Toast.makeText(this, "Button clicked", Toast.LENGTH_LONG).show());