欢迎界面

-----------------------------------------布局---------------------------------------------------

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@mipmap/jd"
    tools:context="test.bawei.jingdong.WelcomeActivity">
<TextView
    android:id="@+id/hand"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />
</android.support.constraint.ConstraintLayout>

--------------------------------------------------------WelcomeActivity-------------------------------

package test.bawei.jingdong;

import android.content.Intent;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

public class WelcomeActivity extends AppCompatActivity {
    private TextView textView;
    private final Handler handler = new Handler() {

        public void handleMessage(android.os.Message msg) {

            if (msg.what == 0) {
                //倒计时完毕进行跳转
                Intent intent = new Intent(WelcomeActivity.this,MainActivity.class);
                startActivity(intent);
                WelcomeActivity.this.finish();
            }
            textView.setText(msg.what+"S");
        }

        ;
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_welcome);
        //获取资源ID
        textView = (TextView) findViewById(R.id.hand);

        //创建一个线程
        new Thread() {
            public void run() {
                try {
                    for (int i = 3; i > 0; i--) {
                        sleep(1000);
                        i--;
                        handler.sendEmptyMessage(i);
                    }

                } catch (Exception e) {
                    e.printStackTrace();
                }
            }

            ;
        }.start();
    }
}