The System system class contains some useful class variables and class methods, which can be called through the System class. But it cannot be instantiated. The System class represents the running platform of the current program, and the program cannot create objects of the System class.
Let’s share the code application of the System class today. By practicing the basic code, you can quickly understand the application of the System class methods and variables.
Related variables and methods:
·System.out: stands for standard output stream ()
·Scanner: generally used to obtain console input
·endsWith: Determine whether this string has a suffix of "0"
·System.err: represents the standard error output stream ()
·System.in: Represents the standard input stream, which is keyboard input ()
·hasNext(): Determine whether there is another input item
· gc(): The function of the function is only to remind the virtual machine that it wants to perform a garbage collection.
·\n: line feed
code segment:

public class SystemClassDemo {
	public static void main(String[] args) {
		//Output
		 System.out.println("standard output stream");
		     		    //keyboard input 
				Scanner sc = new Scanner(System.in);
				while (sc.hasNext()) {
					String string = (String) sc.next();
					 System.out.println("Keyboard input content is:" + string);
					if (string.endsWith("0")) {
						break;
					}
				}

Results of the:

//--------------------------------------------------------------------

		System.out.println("---Get all the environment variables of the system System.getenv()---");
			Map<String,String> map = System.getenv();
			Set<String> keySet = map.keySet();
			for (String key : keySet) {
				System.out.println(key + "===>" + map.get(key));
			}
		 System.out.println("---Get a single system environment variable getenv()---");
			System.out.println(System.getenv("JAVA_HOME")+"\n");
		 System.out.println("---Get system properties getProperties()---");
			System.out.println(System.getProperties()+"\n");
		 System.out.println("---Get a single system property getProperties()---");
			System.out.println(System.getProperty("user.name")+"\n");
		 System.out.println("---System garbage collection gc()---");
			System.gc();

Results of the:

//--------------------------------------------------------------------

	System.out.println("---returns the time difference between the current time and midnight UTC January 1, 1970 currentTimeMillis()---");
		System.out.println(System.currentTimeMillis()+"\n");
	 System.out.println("---nanosecond[1 millisecond(ms)=1000000nanosecond(ns)]nanoTime()---");
		System.out.println(System.nanoTime()+"\n");
	 System.out.println("---returns the exact hashCode value of the specified object identityHashCode()---");
		String str1 = new String("Hello");
		String str2 = new String("Hello");
	    System.out.println(System.identityHashCode(str1) + "\t" + System.identityHashCode(str2));
	 // str1 and str2 are different string objects, so their identityHashCode values ​​are different
	String str3 = "world";
	String str4 = "world";
		System.out.println(System.identityHashCode(str3) + "\t" + System.identityHashCode(str4)+"\n");
	 // str3 and str4 are the same string object, so their identityHashCode value is the same
	 System.out.println("----Stop the running virtual machine, exit the program exit()---");
		System.exit(0);
}
}

Results of the:

//--------------------------------------------------------------------
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