next to previes in java

1st activity of java
public class MainActivity extends AppCompatActivity {
     Button bnext;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

bnext =(Button) findViewById(R.id.b1);
        bnext.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent a =new Intent(MainActivity.this,second.class);
                startActivity(a);
                finish();
            }
        });

    }
}


2nd activity for reverse

public class second extends AppCompatActivity {
Button back;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);

        back=(Button) findViewById(R.id.b2);
      back.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View v) {
              Intent b= new Intent(second.this,MainActivity.class);
              startActivity(b);
              finish();
          }
      });
}

}