How to change CPU frequency via Java code (Or ADB commands via Java code)?

I was able to successfully execute these commands via ADB and was able to change CPU frequency.

adb root
adb shell
cd /sys/devices/system/cpu
echo userspace > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
echo 1152000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
echo 1152000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq

I wanna execute these via Java code, so I tried this approach:

Process suProcess = Runtime.getRuntime().exec("su");
DataOutputStream os = new DataOutputStream(suProcess.getOutputStream());
os.writeBytes("adb shell" + "\n");
os.flush();

but it gives exception on first line. java.io.Exception: Error running exec(). Command: [su] Working directory: null Environment: null

I'm executing these commands in system app, with custom ROM, android 5.0

Can you tell me how to execute these commands in java code? Or do I need to create a bash file to execute these commands?

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