import static java.lang.Math.*;   //静态导入                                   public class StaticImport {	public static void main(String[] args)	{		System.out.println(Math.max(3, 6));		System.out.println(Math.abs(3 - 6));	}}              System.out.println(add(2,3,5));  //重载	}	public static int add(int x,int...args)  //可变参数	{		int sum = x;			for(int i=0;i

枚举　

package cn.think.day1;public class EnumDemo {   //外部类修饰符只有默认和public	public static void main(String[] args) {		WeekDay w = WeekDay.SAT;		System.out.println(WeekDay.valueOf("SUN").toString());		System.out.println(WeekDay.values().length);  //枚举内的元素			}		public enum WeekDay{   //内部类可以有四个修饰符		SUN(1),MON,TUE,WED,THL,FRI,SAT;				private WeekDay(){//必须是私有		System.out.println("first");		}				private WeekDay(int day){			System.out.println("second");		}	}		public enum TraffcLamp{		RED(20){			public TraffcLamp nextLamp(){				return GREEN;			}		},		GREEN(33){			public TraffcLamp nextLamp(){				return YELLOW;			}					},YELLOW(43){			public TraffcLamp nextLamp(){				return RED;			}					};		public abstract TraffcLamp nextLamp();		private int time;		private TraffcLamp(int time){		this.time = time;		}		}	}

反射

Java类----Class	      对象       类		Class cls1 = Date.class;    //获取字节码		                    new Date().getClass();				String str1 = "abc";		Class cls = str1.getClass();		Class cls2 = String.class;	    	        Class cls3 = Class.forName("java.lang.String");		cls1 == cls2;      // true		cls1 == cls3;     //  true				//基本的 Java 类型（boolean、byte、char、short、int、long、float 和 double）和关键字 void 也表示为 Class 对象。