Android系统实现功能：记录可用 RAM 空间,可用 FLASH 空间,CPU 使用率,系统运行时间等信息，并且写出调用的具体做法，请写出完整代码

以下是一个简单的 Android 应用程序，用于获取设备的 RAM 空间、Flash 空间、CPU 使用率和系统运行时间等信息。

import android.app.ActivityManager;
import android.content.Context;
import android.os.Bundle;
import android.os.Environment;
import android.os.StatFs;
import android.os.SystemClock;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // 获取 RAM 空间
        ActivityManager.MemoryInfo memoryInfo = new ActivityManager.MemoryInfo();
        ActivityManager activityManager = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);
        activityManager.getMemoryInfo(memoryInfo);
        long availableRam = memoryInfo.availMem / (1024 * 1024); // 单位：MB

        Log.d(TAG, "可用 RAM 空间：" + availableRam + "MB");

        // 获取 Flash 空间
        File path = Environment.getDataDirectory();
        StatFs stat = new StatFs(path.getPath());
        long blockSize = stat.getBlockSize();
        long availableBlocks = stat.getAvailableBlocks();
        long availableFlash = (availableBlocks * blockSize) / (1024 * 1024); // 单位：MB

        Log.d(TAG, "可用 Flash 空间：" + availableFlash + "MB");

        // 获取 CPU 使用率
        float cpuUsage = getCpuUsage();

        Log.d(TAG, "CPU 使用率：" + cpuUsage + "%");

        // 获取系统运行时间
        long uptime = SystemClock.elapsedRealtime() / 1000; // 单位：秒

        Log.d(TAG, "系统运行时间：" + uptime + "秒");
    }

    private static final String CPU_STAT_PATH = "/proc/stat";
    private static final String CPU_STAT_PATTERN = "cpu\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)";

    private static long lastCpuTime = 0;
    private static long lastCpuIdleTime = 0;

    /**
     * 获取 CPU 使用率
     *
     * @return 返回 CPU 使用率，范围在 0 到 100 之间
     */
    private float getCpuUsage() {
        String stat = "";
        try (BufferedReader reader = new BufferedReader(new FileReader(CPU_STAT_PATH))) {
            stat = reader.readLine();
        } catch (IOException e) {
            Log.e(TAG, "读取 CPU 统计信息失败", e);
        }

        Pattern pattern = Pattern.compile(CPU_STAT_PATTERN);
        Matcher matcher = pattern.matcher(stat);
        if (!matcher.matches()) {
            Log.e(TAG, "无法匹配 CPU 统计信息：" + stat);
            return 0.0f;
        }

        long userTime = Long.parseLong(matcher.group(1));
        long niceTime = Long.parseLong(matcher.group(2));
        long systemTime = Long.parseLong(matcher.group(3));
        long idleTime = Long.parseLong(matcher.group(4));
        long iowaitTime = Long.parseLong(matcher.group(5));
        long irqTime = Long.parseLong(matcher.group(6));
        long softirqTime = Long.parseLong(matcher.group(7));

        long totalCpuTime = userTime + niceTime + systemTime + idleTime + iowaitTime + irqTime + softirqTime;
        long cpuTime = totalCpuTime - idleTime;

        if (lastCpuTime == 0 || lastCpuIdleTime == 0) {
            lastCpuTime = totalCpuTime;
            lastCpuIdleTime = idleTime;
            return 0.0f;
        }

        float cpuUsage = (cpuTime - lastCpuTime) * 100.0f / (totalCpuTime - lastCpuIdleTime);
        lastCpuTime = cpuTime;
        lastCpuIdleTime = idleTime;

        return cpuUsage;
    }
}

该应用程序使用 `ActivityManager`、`Environment` 和 `StatFs` 等 Android API 来获取设备的 RAM 空间和 Flash 空间。它还读取 `/proc/stat` 文件以获取 CPU 使用率，计算系统运行时间使用的是 `SystemClock.elapsedRealtime()` 函数。以上是实现该功能的主要代码。