Java注解

JavaSe5
开始内置了三种注解,定义在Java.lang中

@Override 表示覆盖超类的方法(父类)
@Deprecated 编译器发出警告
@SuppressWarnings　关闭不当的编译器警告信息

另外还有四种元注解

@Target　表示该注解可以用在什么地方
@Retention　表示在什么级别保存该注解信息
@Documented 将此注解包含在Javadoc中
@Inherited 允许子类继承父类的注解

一般来说用到注解的地方很大可能会用到反射以及枚举
因此我举例的时候直接把三者融合在一起

定义注解

@Inherited
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface XXXX{
    public int id();
    public String name()default "zhou";
}

那么既然定义了注解必然要使用注解的

public class Testable(){
    @XXXX(id = 56,name = "blake")
    public void isDemo(){
        System.out.println("..............getAddress()");
    }
}

同样的道理如果用到了注解,那么必须有注解处理器呀!

Class<Testable> testAble = Testable.class;
 Method m = testAble.getDeclaredMethod("isDemo", null);
 //因为没有参数嘛!假如有参数并且恰好是String,则null改   为String.class
 //重点来了
 XXXX xx = m.getAnnotation(XXXX.class);
 //调用即可
 System.out.println("name:" + xx.name());

下面我把编好的例子copy上来
四个自定义注解
FruitAddress

@Inherited
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface FruitAddress {
    public enum Address {
        A1("越南"), A2("缅甸"), A3("菲律宾"), A4("中国海南"), A5("柬埔寨"), A6("文莱"), A7("老挝"), A8("泰国"), A9("新加坡"), A10("马来西亚"), A11("东帝汶"), A12("印度尼西亚");
        private String nameAddress;

        Address(String nameAddress) {
            this.nameAddress = nameAddress;
        }

        /**
         * 获取地址
         * @return
         */
        public String getNameAddress() {
            return nameAddress;
        }
    }

    public Address fruitAddress() default Address.A2;
}

FruitColor

@Documented
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface FruitColor {
    /**
     * 颜色枚举
     */
    public enum Color {
        BLUE, GREEN, RED
    }

    /**
     * 颜色属性
     *
     * @return
     */
    public Color fruitColor() default Color.BLUE;
}

FruitName

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface FruitName {
    public String value() default "";
}

FruitProvider

@Documented
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface FruitProvider {
    /**
     * 供应商编号
     *
     * @return
     */
    public int id() default 01;

    /**
     * 供应商名称
     *
     * @return
     */
    public String name() default "";

    /**
     * 供应商地址
     *
     * @return
     */
    public String address() default "";
}

使用四个注解的class

@FruitProvider(id = 23, name = "blake", address = "china")
public class Apple {

    @FruitName("apple")
    private String appleName;

    @FruitColor(fruitColor = FruitColor.Color.RED)
    private String appleColor;

    @FruitAddress(fruitAddress = FruitAddress.Address.A5)
    public void getAddress() {
        System.out.println("..............getAddress()");
    }


    public Apple() {

    }

    public void displayName() {
        System.out.println("水果的名字是:苹果!");
    }
}

注解处理器的测试 (测试和注解处理器并没有分开都在这个例子中)

public class Demo {
    public static void main(String[] args) {
        try {
            isRun();
            isStart();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void isStart() {
        Class<Apple> appleClass = Apple.class;
        Thread thread = new Thread() {
            @Override
            public void run() {
                try {
                    //获取指定成员变量(字段)
                    Field f1 = appleClass.getDeclaredField("appleName");
                    Field f2 = appleClass.getDeclaredField("appleColor");

                    System.out.println(f1.getName() + " " + f2.getName());

                    //获取成员变量上面的注解
                    FruitName fruitName = f1.getAnnotation(FruitName.class);
                    FruitColor fruitColor = f2.getAnnotation(FruitColor.class);
                    System.out.println(fruitName.value() + "---->");
                    System.out.println(fruitColor.fruitColor().name() + "<----");

                    //获取指定方法
                    Method m1;
                    m1 = appleClass.getDeclaredMethod("getAddress", null);
                    m1 = appleClass.getMethod("getAddress",null); //ps 因为没有参数,如果有传入参数的class
                    System.out.println("method Name:" + m1.getName());
                    //获取方法上的注解
                    FruitAddress fruitAddress = m1.getAnnotation(FruitAddress.class);
                    System.out.println(".." + fruitAddress);
                    if (fruitAddress != null) {
                        System.out.println("address:" + fruitAddress.fruitAddress());
                    } else {
                        System.out.println("point exception");
                    }
                    ;

                    //获取类或者说接口上的注解
                    FruitProvider fruitProvider = appleClass.getAnnotation(FruitProvider.class);
                    if (fruitProvider != null)
                        System.out.println(fruitProvider.address() + " " + fruitProvider.name() + " " + fruitProvider.id());
                } catch (NoSuchFieldException e) {
                    System.out.println("exception:" + e.getMessage());
                    e.printStackTrace();
                } catch (NoSuchMethodException ex) {
                    System.out.println("exception:" + ex.getMessage());
                    ex.printStackTrace();
                }

            }
        };
        thread.start();
    }

    public static void isRun() {
        Class<Apple> appleClass = Apple.class;
        Field[] fields = appleClass.getDeclaredFields();
        for (Field f : fields) {//遍历
            FruitColor fruitColor = f.getAnnotation(FruitColor.class);//获取注解在字段(成员变量)上的注解对象
            FruitName fruitName = f.getAnnotation(FruitName.class);
            if (fruitColor != null) {
                System.out.println("color:" + fruitColor.fruitColor());
            }
            if (fruitName != null) {
                System.out.println("name:" + fruitName.value());
            }
        }
    }
}

基本上用到了Java的线程,注解,反射,枚举这四个基础知识.如有问题请留言!

Java注解

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