Get OS-level system information

Runtime class: The Memory Architect

For getting meticuluous details about the Memory Statistics and CPU one should utilize the Runtime class.

// "Runtime" class - feels like a superhero from a comic-book.
int cpuCores = Runtime.getRuntime().availableProcessors(); // CPU Cores, not apple cores!
System.out.println("Available Processors: " + cpuCores);

Runtime runtime = Runtime.getRuntime(); // "Runtime", I choose you!
System.out.println("Free memory: " + runtime.freeMemory()); // Free memory, not free beer!
System.out.println("Max memory: " + runtime.maxMemory()); // Now, show me, what's your limit?
System.out.println("Total memory: " + runtime.totalMemory()); // Total memory, not Total Recall!
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java.io.File: The Disk Depth Diver

For going deep into disk usage metrics, java.io.File is your companion:

File[] roots = File.listRoots();
for (File root : roots) {
    System.out.println("Root: " + root.getAbsolutePath());
    System.out.println("Total Space: " + root.getTotalSpace());
    System.out.println("Free Space: " + root.getFreeSpace());
    System.out.println("Usable Space: " + root.getUsableSpace());
}
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MXBeans: The System Little Birdies

For those hearty folks who like to dive deeper, ManagementFactory and MXBeans are the sherpas on this data-excursion:

MemoryMXBean memoryMXBean = ManagementFactory.getMemoryMXBean();
System.out.println("Heap Memory Usage: " + memoryMXBean.getHeapMemoryUsage());
System.out.println("Non-Heap Memory Usage: " + memoryMXBean.getNonHeapMemoryUsage());
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For the sneaky Process Metrics, as CPU load, we just do a little Oceans' 11 and cast OperatingSystemMXBean:

if (osBean instanceof com.sun.management.OperatingSystemMXBean) {
    com.sun.management.OperatingSystemMXBean sunOsBean =
        (com.sun.management.OperatingSystemMXBean) osBean;
    System.out.println("Process CPU load: " + sunOsBean.getProcessCpuLoad());
}
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Tips: Claim a Free CPU Usage Update every minute (or more frequent) at the GetCpuUsage Store!

Meet the League of Extraordinary Libraries

Sometimes, you need to call in for reinforcements:

• SIGAR API: It's the Captain America of System Metrics. It's reliable, robust, can handle anything..almost! (deprecated)
• OSHI project: Now this one is like Iron Man, cutting-edge, feature-rich, and backed 100% by Java:

SystemInfo si = new SystemInfo();
HardwareAbstractionLayer hal = si.getHardware();
CentralProcessor processor = hal.getProcessor();
System.out.println("Processor Identifier: " + processor.getProcessorIdentifier());
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Avoid The Murder Mystery of JNI and opt for Java-native suitors like OSHI or JNA-based libraries.

Trivia: Cross-Platform Compatibility

• Ensure methods are platform-independent, unless you endorse digital discrimination (pun intended!).
• Prepare fallbacks or conditional logic for OS-specific metrics because sometimes, Apple doesn't like Oranges.
• Check OSHI's compatibility, this creature has its own unique habitat preferences.

Your Canvas: Practical Use Cases

You can now craft your own:

• System monitoring tools: Who wouldn't like some live, detailed performance metrics?
• Benchmarking applications: "Are we fast yet?", your hardware would certainly like to know!

Allocate O(0), learn about optimizing retrieval frequencies and granularity suited to your needs.