Java-day13(枚举与注解)

枚举与注解

枚举

1.自定义枚举

如果枚举只有单个成员，则可以作为单例模式的实现方式

public class test{
public static void main(String[] args) {              
    Season spring = Season.spring;
    System.out.println(spring);
    spring.show();
    System.out.println(spring.getSeasonName());
}
}
//枚举类
class Season{
    //1.提供类的属性的私有，不可修改
    private final String seasonName;
    private final String seasonDesc;
    //声明为final的属性，在构造器中初始化
    private Season(String seasonName, String seasonDesc){
        this.seasonDesc = seasonDesc;
        this.seasonName = seasonName;
    }
    //通过公共的方法来调用属性
    public String getSeasonName(){
        return  seasonName;
    }
    public String getSeasonDesc(){
        return  seasonDesc;
    }
    //创建枚举类对象：将类的对象声明为public static final
    public static final Season spring = new Season("spring", "万物复苏");
    public static final Season summer = new Season("summer", "烈日炎炎");
    public static final Season autumn = new Season("autumn", "秋高气爽");
    public static final Season winter = new Season("winter", "寒冬来临");
    public String toString(){
        return "Season [ Name: " + seasonName + ", Desc: " + seasonDesc + "]";
    }
    public void show(){
        System.out.println("又是这个季节");
    }
}

2.使用enum关键字定义枚举类

enum关键字是JDK1.5新增的
枚举类的主要方法

public class test1{
public static void main(String[] args) {              
    Season1 spring = Season1.spring;
    System.out.println(spring); 
    spring.show();
    System.out.println(spring.getSeasonName()); 
    System.out.println(); 

    //1.枚举的values()方法
    Season1[] seasons = Season1.values();
    for(int i = 0;i < seasons.length;i++){
        System.out.println(seasons[i]); 
    }    
    System.out.println(); 
    //2.枚举的valueof(String name)方法：要求传入的形参name必须是枚举对象的名字，否则报异常IllegalArgumentException
    String str = "spring";
    Season1 sea = Season1.valueOf(str);
    System.out.println(sea); 
}
}
//枚举类
enum Season1{
    spring ("spring", "万物复苏"),
    summer ("summer", "烈日炎炎"),
    autumn ("autumn", "秋高气爽"),
    winter ("winter", "寒冬来临");
    private final String seasonName;    
    private final String seasonDesc;
    
    private Season1(String seasonName, String seasonDesc){
        this.seasonDesc = seasonDesc;
        this.seasonName = seasonName;
    }
    
    public String getSeasonName(){
        return  seasonName;
    }
    public String getSeasonDesc(){
        return  seasonDesc;
    }
    public String toString(){ 
        return "Season [ Name: " + seasonName + ", Desc: " + seasonDesc + "]"; 
    }
    public void show(){
        System.out.println("又是这个季节");
    }
}

3.实现接口的枚举类

• 可以让枚举类的对象调用同一套被重写的抽象方法，执行的效果相同

例：

public class test1{
public static void main(String[] args) {         
    Season1 spring = Season1.spring;
    System.out.println(spring);
    spring.show();
    System.out.println(spring.getSeasonName());
    System.out.println();
}
}
enum Season1{
    spring ("spring", "万物复苏"),
    summer ("summer", "烈日炎炎"),
    autumn ("autumn", "秋高气爽"),
    winter ("winter", "寒冬来临");
    private final String seasonName;
    private final String seasonDesc;
    
    private Season1(String seasonName, String seasonDesc){
        this.seasonDesc = seasonDesc;
        this.seasonName = seasonName;
    }
    
    public String getSeasonName(){
        return  seasonName;
    }
    public String getSeasonDesc(){
        return  seasonDesc;
    }
    public String toString(){
        return "Season [ Name: " + seasonName + ", Desc: " + seasonDesc + "]";
    }
    public void show(){
        System.out.println("又是这个季节");
    }
}

• 可以让不同的枚举类的对象调用被重写的抽象方法，执行的效果不同（相当于让每个对象重写自己的抽象方法）

例：

public class test2{
public static void main(String[] args) {  
    Season1 spring = Season1.spring;
    System.out.println(spring);
    spring.show();
    System.out.println(spring.getSeasonName());
    System.out.println();
}

interface info{
    void show();
}
enum Season1 implements info{
    spring ("spring", "万物复苏"){
        public void show(){
            System.out.println("春天到了！");  
        }
    },
    summer ("summer", "烈日炎炎"){
        public void show(){
            System.out.println("夏天到了！");
        }
    },
    autumn ("autumn", "秋高气爽"){
        public void show(){
            System.out.println("\u79CB天到了！");
        }
    },
    winter ("winter", "寒冬来临"){
        public void show(){
            System.out.println("冬天到了！");
        }
    };
    private final String seasonName;
    private final String seasonDesc;
    
    private Season1(String seasonName, String seasonDesc){
        this.seasonDesc = seasonDesc;
        this.seasonName = seasonName;
    }
    
    public String getSeasonName(){
        return  seasonName;
    }
    public String getSeasonDesc(){
        return  seasonDesc;
    }
    public String toString(){
        return "Season1 [ Name: " + seasonName + ", Desc: " + seasonDesc + "]";
    }
}
}

注释（Annotation）

• 从JDK5.0开始增加对元数据的支持，即注解（代码中的特殊标记）

• 可用于修饰包，类，构造器，方法，成员变量，参数，局部变量的声明，保存在注解的"name=value"对中

• 能被用来为程序元素（类，方法等）设置元数据

4.内置的基本注释类型（3个）

@Override

限定重写父类方法，只能用于方法
例：

public class test{
    public static void main(String[] args) {           
        Person p = new Student();
        p.info();
    }
}
class Student extends Person{
    @Override
     public void info(){
        System.out.println("学生表演吃瓜！");
    }
}
class Person{//个人信息
	private String name;  //姓名
	private int age;      //年龄
	private String sex;   //性别

	public Person(String name,int age,String sex){
		super();
		this.name = name;
		this.age = age;
		this.sex = sex;
	}
	public Person(){
		super();
	}
    public void info(){
        System.out.println("人\u8868\u6F14吃瓜！");
    }
}

@Deprecated

用于表示某个程序元素(类，方法等)已过时
例：

public class test6 {
    public static void main(String[] args) {      
        Person p = new Student();
        p.info();
    }
}
class Student extends Person{
     public void info(){
        System.out.println("学生表演吃瓜！");
    }
}
@Deprecated
class Person{//个人信息
	private String name;  //姓名
	private int age;      //年龄
	private String sex;   //性别

	public Person(String name,int age,String sex){
		super();
		this.name = name;
		this.age = age;
		this.sex = sex;
	}
	public Person(){
		super();
	}
    public void info(){
        System.out.println("人\u8868\u6F14吃瓜！");
    }
}

@SuppressWarnings

抑制编译器警告

import java.util.ArrayList;
import java.util.List;
public class test {
   public static void main(String[] args) {      
	@SuppressWarnings({"rawtypes","unused"})
	//抑制没有使用泛型，没有使用的警告
	List list = new ArrayList();
	}
}

5.自定义注解

例：

public @interface test7 {
   String value() default "hello";
}
//使用
public class test6 {
	@test7(value = "qwerq")
	    public static void main(String[] args) { 
    }
}

6.元注解（4个）

修饰其他注解的定义，该注解具体有

@Retention

只能修饰一个注解的定义，指定该注解可以保留多长时间，@Retention中有一个RetentionPolicy类型的成员变量，使用时，必须给这个成员变量指定值（值：

• SOURCE(编译器直接放弃这种注解)
• CLASS(编译器将注释记录到class文件中,运行时,JVM不保留注解,这是默认值)
• RUNTIME(编译器将注释记录到class文件中,运行时,JVM保留注解,程序可以通过反射获取该注解)）

import java.lang.annotation.Retention;                                                        
import java.lang.annotation.RetentionPolicy;

@Retention(RetentionPolicy.CLASS)
public @interface test7 {
   String value() default "hello";
}

@Target

指定被修饰的注解能用于哪些程序元素，@Target中有一个value的成员变量

@Documented

将被javadoc工具提取成文件，@Retention值必须是RUNTIME

@Inherited

被它修饰的注解将具有继承性，某个类使用了此注解，那它的子类将自动具有该注释

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参考资料：
尚硅谷宋红康20天搞定Java基础中部