Enum枚举类的学习

小咪咪 2022-02-14 06:21 362阅读 0赞

//构造器是不允许其他类型的修饰,只能private,所以枚举类无法在类外进行初始化,保证了它不会多出几个另外的实例
    //所以枚举的实例本身也就是一个初始化好的类的示例(调用了构造函数初始化)
    //DAY调用了EnumTest2(),SECOND(100,"秒")调用了EnumTest2(Integer code,String message)

import java.util.HashMap;
    import java.util.Map;
    
    public enum EnumTest2 {
    
    	DAY,MOUTH,YEAR,SECOND(100,"秒");
    	
    	private Integer code;
    	private String message;
    	//构造器是不允许其他类型的修饰,只能private
    	//所以枚举的实例本身也就是一个初始化好的类的示例(调用了构造函数初始化)
    	//DAY调用了EnumTest2(),SECOND(100,"秒")调用了EnumTest2(Integer code,String message)
    	private EnumTest2(Integer code,String message) {
    		
    	}
    	
    	private EnumTest2() {
    	}
    	private static final Map<String, EnumTest2> map = new HashMap<String, EnumTest2>();
    	static {
    	//学习遍历枚举类的方法:values()是枚举类自带的数组,包含它所有的实例
    		for (EnumTest2 enumTest : values()) {
    				//name是默认属性?是的,代表实例定义的命名
    			map.put(enumTest.name(), enumTest);
    		}
    	}
    	
    	public static void main(String[] args) {
    		//{YEAR=YEAR, MOUTH=MOUTH, DAY=DAY}
    		System.out.println(map.toString());
    	}
    }

import java.util.HashMap;
    import java.util.Map;
    
    public enum EnumTest {
    	//能这么写,本质上是因为采用了默认的构造函数的原因,每一个枚举类的定义相当于调用了对应的构造函数,构造了自己
    	//也就是已经初始化好的类的一个实例
    	DAY,MOUTH,YEAR;
    	
    	private static final Map<String, EnumTest> map = new HashMap<String, EnumTest>();
    	static {
    		for (EnumTest enumTest : values()) {
    			map.put(enumTest.name(), enumTest);
    		}
    	}
    	
    	public static void main(String[] args) {
    		//{YEAR=YEAR, MOUTH=MOUTH, DAY=DAY}
    		System.out.println(map.toString());
    	}
    }

HttpMethod
    
    public enum HttpMethod {
    
    	GET, HEAD, POST, PUT, PATCH, DELETE, OPTIONS, TRACE;
    
    	//定义给一个Map,根据string的值来获取对应的枚举类型.
    	
    	private static final Map<String, HttpMethod> mappings = new HashMap<String, HttpMethod>(8);
    	//初始化的时候,将自己所有的枚举类加入map中.
    	static {
    	//学习遍历枚举类的方法:values()是枚举类自带的数组,包含它所有的实例
    		for (HttpMethod httpMethod : values()) {
    		//name是默认属性?是的,代表实例定义的命名
    			mappings.put(httpMethod.name(), httpMethod);
    		}
    	}
    
    
    	/**
    	 * Resolve the given method value to an {@code HttpMethod}.
    	 * @param method the method value as a String
    	 * @return the corresponding {@code HttpMethod}, or {@code null} if not found
    	 * @since 4.2.4
    	 */
    	public static HttpMethod resolve(String method) {
    		return (method != null ? mappings.get(method) : null);
    	}
    
    
    	/**
    	 * Determine whether this {@code HttpMethod} matches the given
    	 * method value.
    	 * @param method the method value as a String
    	 * @return {@code true} if it matches, {@code false} otherwise
    	 * @since 4.2.4
    	 */
    	public boolean matches(String method) {
    		return (this == resolve(method));
    	}
    
    }