System

获取系统属性：

import java.util.*;
public class Practice_1 {
    public static <K, V> void main(String[] args) {
        Properties prop = System.getProperties();
        for(Object obj : prop.keySet())
        {
            String value = (String)prop.get(obj);
            System.out.println(obj+"..."+value);
        }
    }
}