Task: Linux CPU utilization
C: #include<stdlib.h>
#include<string.h>
#include<unistd.h>
#include<stdio.h>

int main(int argC,char* argV[])
{
	char str[100];
	const char d[2] = " ";
	char* token;
	int i = 0,times,lag;
	long int sum = 0, idle, lastSum = 0,lastIdle = 0;
	long double idleFraction;
	
	if(argC!=3)
		printf("Usage : %s <number of times /proc/stat should be polled followed by delay in seconds.>",argV[0]);
	
	else{
		times = atoi(argV[1]);
		lag = atoi(argV[2]);
		
		while(times>0){
			FILE* fp = fopen("/proc/stat","r");
	                i = 0;
			fgets(str,100,fp);
			fclose(fp);
			token = strtok(str,d);
	                sum = 0;
			while(token!=NULL){
				token = strtok(NULL,d);
				if(token!=NULL){
					sum += atoi(token);
			
				if(i==3)
					idle = atoi(token);
		
				i++;
			        }
		        }
	                idleFraction = 100 - (idle-lastIdle)*100.0/(sum-lastSum);
		        printf("Busy for : %lf %% of the time.", idleFraction);
	
		        lastIdle = idle;
		        lastSum = sum;
	
		
		        times--;
		        sleep(lag);
		}	
	}
	return 0;
}

Java: import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.text.NumberFormat;
import java.time.Duration;
import java.util.Timer;
import java.util.TimerTask;


public class Main {

    public static void main(String[] args) throws FileNotFoundException {
        
        final var period = Duration.ofSeconds(1);
        new Timer().schedule(new CpuUtilizationTask(), 0, period.toMillis());
    }

    
    static class CpuUtilizationTask extends TimerTask {

        private final String STAT_FILE_HEADER = "cpu  ";
        private final NumberFormat percentFormatter;
        private final RandomAccessFile statPointer;
        long previousIdleTime = 0, previousTotalTime = 0;

        public CpuUtilizationTask() throws FileNotFoundException {
            this.percentFormatter = NumberFormat.getPercentInstance();
            percentFormatter.setMaximumFractionDigits(2);
            var statFile = new File("/proc/stat");
            
            this.statPointer = new RandomAccessFile(statFile, "r");
        }

        @Override
        public void run() {

            try {
                var values = statPointer.readLine()
                        .substring(STAT_FILE_HEADER.length())
                        .split(" ");

                
                var idleTime = Long.parseUnsignedLong(values[3]);
                var totalTime = 0L;
                for (String value : values) {
                    totalTime += Long.parseUnsignedLong(value);
                }

                var idleTimeDelta = idleTime - previousIdleTime;
                var totalTimeDelta = totalTime - previousTotalTime;
                var utilization = 1 - ((double) idleTimeDelta) / totalTimeDelta;

                
                System.out.println(percentFormatter.format(utilization));

                previousIdleTime = idleTime;
                previousTotalTime = totalTime;

                
                statPointer.seek(0);
            } catch (IOException ioException) {
                ioException.printStackTrace();
            }
        }

    }
}