The Java System class

Class System Overview

java.lang.System in class provides a number of static methods, you can get information or system-level operating system-related, in the API documentation System class, commonly used methods are:

• public static long currentTimeMillis (): returns the current time in milliseconds. In fact, currentTimeMillis method is to get the millisecond time difference between the current system and at 00:00 on January 1st, 1970 points

public  class SystemDemo {
     public  static  void main (String [] args) {
         // get the current time value in milliseconds 
        System.out.println (System.currentTimeMillis ()); // 1575800449598 
    } 
}

• public static void arraycopy (Object src, int srcPos, Object dest, int destPos, int length): copy the data specified in the array to another array. A copy operation of the array system-level, high performance. System.arraycopy method has five parameters, meaning respectively:

Package Demo05; 

Import java.util.Arrays; 

public  class SystemArrayCopy {
     public  static  void main (String [] args) {
          / * 

            the src - the source array. 
            srcPos - start position (start index) in the source array. 
            dest - the destination array. 
            destPos - starting position of the target data. 
            length - the number of array elements to be copied. 
        Exercise: 
            The first three in the src array elements are copied to three positions on the array dest 
                before copying element: 
                src array element [1,2,3,4,5], dest array element [6,7,8, 9,10] 
                after copying elements: 
              * / 
        // definition of the source array 
        int [] = {the src. 1, 2,. 3,. 4,. 5 };
         //Define the target array 
        int [] = {dest. 6,. 7,. 8,. 9, 10 }; 
        System.out.println ( "before copying:" + of Arrays.toString (dest));
         // Use the System class source arraycopy the first three elements of the array are copied to three positions on the target array 
        System.arraycopy (the src, 0, dest, 0,. 3 ); 
        System.out.println ( "after copying:" + of Arrays.toString (dest)) ; 
    } 
}

The result of code execution