אנדרויד 1

public class MainActivity extends AppCompatActivity {

    private TextView tv1;
    private Button btn1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        tv1 = (TextView) findViewById(R.id.txt1);
        btn1 = (Button) findViewById(R.id.b1);

        
        btn1.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v){

                Toast.makeText(getApplicationContext(),"jadek",Toast.LENGTH_SHORT).show();
            }
        });

    }
}