使用intent跳转的时候点一下就关闭了，不知道怎么回事，请教一下大神们

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.dell.myapplication">

<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".SecondActivity">

</activity>
</application>

</manifest>


mainactivity的代码：
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

Button btn=this.findViewById(R.id.button);
btn.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v) {
//Toast.makeText(MainActivity.this, "你点击了按钮", Toast.LENGTH_SHORT).show();
Intent intent = new Intent();
intent.setClass(MainActivity.this,SecondActivity.class );
startActivity(intent);
finish();
}
});

}