UUID、Optional（2021-12-15）

package demo;

import java.util.Optional;
import java.util.UUID;

interface IMessage{
	public String getContent();
}

class MessageImpl implements IMessage{
	public String getContent() {
		return "这是消息内容。";
	}
}

class MessageUtil{
	public static Optional<IMessage> getMessage() {		
		return Optional.of(new MessageImpl());				//把IMessage对象包装在Optional对象中，预先对参数为null的情况识别并处理
	}
	public static void useMessage(IMessage msg) {
		System.out.println(msg.getContent());
	}
}

public class Demo {

	public static void main(String[] args) {
		System.out.println(UUID.randomUUID());				//自动生成无重复的字符串，还有fromString方法根据字符串获取UUID
		
		IMessage msg = MessageUtil.getMessage().get();		//从Optional包装中取出IMessage对象
		MessageUtil.useMessage(msg);
	}

}