Java 学习之常量定义与枚举值定义

布满荆棘的人生 2023-06-16 07:25 28阅读 0赞

package javaObject;
    
    import com.sun.glass.events.WheelEvent;
    
    public class javaEnum { 
    	public static void main(String[] args) { 
    		
    		/* * 无论是int常量还是String常量，使用这些常量来表示一组枚举值的时候，有一个严重的问题就是，编译器无法检查每个值的合理性。 * * enum定义的枚举类，其类型就是class * 无法通过new操作符创建enum的实例 * * enum定义枚举优势： * 1 enum常量本身带有类型信息，编译器会自动检查出类型错误 * 2 其次，不可能引用到非枚举的值，因为无法通过编译 * 3 不同类型的枚举不能互相比较或者赋值，因为类型不符。 * */
    		
    		// 整型常量判断
    		int day = Weekday.SUN;
    		switch (day) { 
    		case Weekday.SUN: System.out.println("今天是星期日");break;
    		case Weekday.MON: System.out.println("今天是星期一");break;
    		case Weekday.TUE: System.out.println("今天是星期二");break;
    		case Weekday.WED: System.out.println("今天是星期三");break;
    		case Weekday.THU: System.out.println("今天是星期四");break;
    		case Weekday.FRI: System.out.println("今天是星期五");break;
    		case Weekday.SAT: System.out.println("今天是星期六");break;
    		default:
    			break;
    		}
    		
    		// 字符型常量判断
    		String fruit = Fruit.apple;
    		if (Fruit.apple.equals(fruit)) { 
    			System.out.println("今天买了苹果");
    		} else if (Fruit.orange.equals(fruit)) { 
    			System.out.println("今天买了橙子");
    		} else if (Fruit.banana.equals(fruit)) { 
    			System.out.println("今天买了香蕉");
    		}
    		
    		// 枚举判断
    		WeekName weekDay = WeekName.SAT;
    		if (weekDay == WeekName.SAT) { 
    			System.out.println("周六去踢足球");
    		} else { 
    			System.out.println("不是周六不去足球");
    		}
    		
    		System.out.println("返回常量名：" + WeekName.SUN.name());
    		
    		Launch launch = Launch.Monlaunch;
    		System.out.println(launch.launchDay + "带了 " + launch.toString());
    	}
    }
    
    // 整型常量
    class Weekday { 
    	public static final int SUN = 0;
    	public static final int MON = 1;
    	public static final int TUE = 2;
    	public static final int WED = 3;
    	public static final int THU = 4;
    	public static final int FRI = 5;
    	public static final int SAT = 6;
    }
    
    // 字符型常量
    class Fruit { 
    	public static final String apple = "apple";
    	public static final String banana = "banana";
    	public static final String orange = "orange";
    }
    
    // 枚举
    enum WeekName { 
    	SUN, MON, TUE, WED, THU, FRI, SAT;
    }
    
    // 枚举 
    enum Launch { 
    	Monlaunch("星期一", 2,"鸡翅+生菜"), Tuelaunch("星期二", 3,"瘦肉+炸豆腐+西芹"), Wedlaunch("星期三", 2,"鸡腿+茼蒿"), Thulaunch("星期四", 2,"腐竹+瘦肉"),Frilaunch("星期五", 1,"鱼");
    
    	// enum的字段强烈建议声明为final
    	public final String launchDay;
    	public final int lauchCount;
    	private final String launchName;
    	
    	// enum的构造方法要声明为private
    	private Launch(String day, int count, String name) { 
    		this.launchDay = day;
    		this.lauchCount = count;
    		this.launchName = name;
    	}
    	
    	@Override
    	public String toString() { 
    		return this.lauchCount + "个菜：" + this.launchName;
    	}
    }