创建工具类如下：

package com.example.hxd.gittest;

import android.app.Activity;

import java.util.ArrayList;
import java.util.List;

/**
 * 统一退出程序的操作
 */
class ActivitySetting {
    //创建集合存储打开的Activity
    static List<Activity> activityList = new ArrayList<>();

    //添加打开的Activity到集合
    static void addActivity(Activity activity) {
        activityList.add(activity);
    }

    //移除集合内部的Activity
    static void removeActivity(Activity activity) {
        activityList.remove(activity);
    }

    //关闭所有的Activity
    static void finishAllActivity() {
        for (Activity activity : activityList) {
            if (!activity.isFinishing()) {
                activity.finish();
                //杀死当前应用进程
                android.os.Process.killProcess(android.os.Process.myPid());
            }
        }
    }
}

在BaseActivity内部添加如下代码：

package com.example.hxd.gittest;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class BaseActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_base);
        //添加当前操作的Activity到集合内部
        ActivitySetting.addActivity(this);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        //移除无用的Activity
        ActivitySetting.removeActivity(this);
    }
}

具体Activity内部代码如下：

  btnSecond.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //点击按钮退出程序，杀死进程
                ActivitySetting.finishAllActivity();
            }
        });