System

• The System class holds a collection of Static methods and variables.

• The standard input, output, and error output of the Java run time are stored in the in, out, and err variables.

• The methods defined by the System are as follows where most of them throws SecurityException if the operation is not permitted by the manager.

currentTimeMillis( )

• This is the method of System class which returns the time taken for executing a various parts of program in milliseconds.

// Timing program execution.
public class Elapsed 
{
 public static void main(String args[]) 
 {
 long start, end;
 System.out.println("Timing a for loop from 0 to 100,000,000");
 // time a for loop from 0 to 100,000,000
 start = System.currentTimeMillis(); // get starting time

   System.out.println("start time is::"+start);
   for(long i=0; i < 100000000L; i++) ;
 end = System.currentTimeMillis();   // get ending time


   System.out.println("End time is::"+end);
   System.out.println("Elapsed time: " + (end-start));
 }
}

Output:

Timing a for loop from 0 to 100,000,000
start time is::1496659694927
End time is::1496659694988
Elapsed time: 61

• We can use nanoTime() method to get the time in nanoseconds which is depends on the system that allows or not.

// Timing in nanoseconds program execution.
public class Elapsed 
{
 public static void main(String args[]) 
 {
 long start, end;
 System.out.println("Timing a for loop from 0 to 100,000,000");
 // time a for loop from 0 to 100,000,000
 start = System.nanoTime(); // get starting time

   System.out.println("start time is::"+start);
   for(long i=0; i < 100000000L; i++) ;
 end = System.nanoTime();   // get ending time


   System.out.println("End time is::"+end);
   System.out.println("Elapsed time: " + (end-start));
 }
}

Output:

Timing a for loop from 0 to 100,000,000
start time is::21822483561178078
End time is::21822483621049032
Elapsed time: 59870954

// Using arraycopy().
public class ACDemo 
{
 static byte a[] = { 65, 66, 67, 68, 69, 70, 71, 72, 73, 74 };
 static byte b[] = { 77, 77, 77, 77, 77, 77, 77, 77, 77, 77 };

  public static void main(String args[]) 
 {

 System.out.println("a = " + new String(a));
 System.out.println("b = " + new String(b));
 System.arraycopy(a, 0, b, 0, a.length);
 System.out.println("a = " + new String(a));
 System.out.println("b = " + new String(b));
 System.arraycopy(a, 0, a, 1, a.length - 1);
 System.arraycopy(b, 1, b, 0, b.length - 1);
 System.out.println("a = " + new String(a));
 System.out.println("b = " + new String(b));
 }

}

Output:

a = ABCDEFGHIJ
b = MMMMMMMMMM
a = ABCDEFGHIJ
b = ABCDEFGHIJ
a = AABCDEFGHI
b = BCDEFGHIJJ

Environment Properties

• The following are the properties which are available in all cases.

• We can obtain the value of these properties by calling System.getProperty( ) method.

public class SystemDemo {

   public static void main(String[] args) {

      // prints the name of the system property
      System.out.println(System.getProperty("user.dir"));

      // prints the name of the Operating System
      System.out.println(System.getProperty("os.name"));

      // prints Java Runtime Version
      System.out.println(System.getProperty("java.runtime.version" ));
   }
}

Output:

/web/com/1496661268_134943

Linux

1.8.0_65-b17