Timer

import android.os.CountDownTimer;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {
    Counter crt;
    TextView tvCtr;
    Button btn;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn = (Button) findViewById(R.id.start);
        tvCtr =  (TextView) findViewById(R.id.tvCtr);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //10000 = 10 seconds
                crt=new Counter(10001,1);
                crt.start();
            }
        });
    }

    public class Counter extends CountDownTimer {

        Counter(long mSeconds,long range){
            super(mSeconds,range);
        }
        @Override
        public void onTick(long millisUntilFinished) {
            tvCtr.setText(String.valueOf(millisUntilFinished/1000));
        }

        @Override
        public void onFinish() {
            tvCtr.setText("Done");
        }
    }
}