java lang math

学习java的第30天，以下是packge的示例代码

package common;

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

@Target(ElementType.PACKAGE)

@Retention(RetentionPolicy.RUNTIME)

public @interface PriorityLevel {

int value();

}

@PriorityLevel(2)

package util;

import java.math.BigDecimal;

import common.PriorityLevel;

class LogLevel{

public static final String LOG_LEVEL = "DBUG";

public static final BigDecimal PI = new BigDecimal("3.1416");

}

package util;

import common.PriorityLevel;

public class StrTool {

public static void main(String[] args) {

System.out.println(LogLevel.PI);

StrTool strTool = new StrTool();

Package pkg = strTool.getClass().getPackage();

PriorityLevel priorityLevel = pkg.getAnnotation(PriorityLevel.class);

System.out.println(priorityLevel.value());

}

}