1//View.java#findViewById
2@Nullable
3public final <T extends View> T findViewById(@IdRes int id) {
4    if (id == NO_ID) {
5        return null;
6    }
7    return findViewTraversal(id);
8}

1findViewById(1001);

1//这个注解提示修饰的值可以为null
2@Retention(SOURCE)
3@Target({METHOD, PARAMETER, FIELD})
4public @interface Nullable {
5}

1//这个注解提示修饰的值可以为null
2@Documented
3@Retention(CLASS)
4@Target({METHOD, PARAMETER, FIELD, LOCAL_VARIABLE})
5public @interface IdRes {
6}

 1//MainActivity.java
 2@Override
 3protected void onCreate(@Nullable Bundle savedInstanceState) {
 4    super.onCreate(savedInstanceState);
 5    setContentView(R.layout.activity_main);
 6    InjectUtils.injectView(this);
 7
 8    Intent intent = new Intent(this, SecondActivity.class)
 9        .putExtra("name", "23"); //传10个参数
10    startActivity(intent);
11}
12//MainActivity.class
13//与上面的区别就是没有override修饰，并且setContentView显示的为数字
14protected void onCreate(@Nullable Bundle savedInstanceState) {
15    super.onCreate(savedInstanceState);
16    this.setContentView(2131296284);
17    InjectUtils.injectView(this);
18    Intent intent = (new Intent(this, MainActivity.SecondActivity.class)).putExtra("name", "23");
19    this.startActivity(intent);
20}

 1public class MyProcessor extends AbstractProcessor {
 2
 3    @Override
 4    public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnvironment) {
 5        Messager messager = processingEnv.getMessager();
 6        messager.printMessage(Diagnostic.Kind.NOTE, "================================");
 7
 8        return false;
 9    }
10}

 1//自定义一个注解类，让注解标注的方法，属性和传入参数都限制只使用特定的输入，不然报错
 2//@MyAnnotation.java
 3//限定词IntDef，即虽然定义的是int类型，但是必须使用下面限定的写法，不然报错
 4//Target限制作用域，根据前文可知，这里限制了传参，属性和方法
 5//Retention定义了场景为源码阶段，编译生成的class类型不会出现这个注解
 6//在类里面定义的几个变量，默认为public static final修饰，可以省略不写
 7@IntDef(value = {MyAnnotation.custom_1,
 8        MyAnnotation.custom_2,
 9        MyAnnotation.custom_3,
10        MyAnnotation.custom_4,
11        MyAnnotation.custom_5,
12        MyAnnotation.custom_6})
13@Target({ElementType.PARAMETER,ElementType.FIELD,ElementType.METHOD})
14@Retention(RetentionPolicy.SOURCE)
15public @interface MyAnnotation {
16    int custom_1 = 1;
17    int custom_2 = 2;
18    int custom_3 = 3;
19    int custom_4 = 4;
20    int custom_5 = 5;
21    int custom_6 = 6;
22}

 1//在activity里面简单的写入属性i，传参state，方法getState
 2public class MainActivity extends AppCompatActivity {
 3    @MyAnnotation
 4    private int i = 1;//错误，应该修改成private int i = MyAnnotation.custom_1;
 5
 6    public void setState(@MyAnnotation int state){
 7        this.i = state;
 8    }
 9    
10    @MyAnnotation
11    public int getState(){
12        return 1;//错误应该改成 return MyAnnotation.custom_1;
13    }
14
15    @Override
16    protected void onCreate(@Nullable Bundle savedInstanceState) {
17        super.onCreate(savedInstanceState);
18        setContentView(R.layout.activity_main);
19
20        this.setState(1);//错误，应该修改成this.setState(MyAnnotation.custom_1);
21    }
22}

1@Target(ElementType.METHOD)
2@Retention(RetentionPolicy.CLASS)
3public @interface Login {
4}

1@Login
2public void jumpA(){
3startActivity(new Intent(this,AActivity.class));
4} 
5public void jumpB(){
6startActivity(new Intent(this,BActivity.class));
7}

 1public static void injectView(Activity activity){
 2    Class<? extends Activity> cls = activity.getClass();
 3    //获得此类所有的成员
 4    //class获取属性的方式
 5    //getField获得自己和父类的成员（不包括private，只能是public）
 6    //getDecleredField只能获得自己的成员（不包括父类，所有作用域）
 7    //一般可用cls.getSuperclass().getDecleredField()获取父类所有属性
 8    Field[] declaredFields = cls.getDeclaredFields();
 9    for(Field field : declaredFields){
10        //判断属性是否被injectview注解声明
11        if(field.isAnnotationPresent(InjectView.class)){
12            InjectView injectView = filed.getAnnotation(InjectView.class);
13            //获得了注解中的设置id
14            int id = injectView.value();
15            View view = activity.findViewById(id);
16            //反射设置属性的值
17            filed.setAccessiable(true);//设置访问权限，允许操作private的属性
18            //filed就是具体的view对象比如tv，activity为限定的class类，view为tv设置的值，即tv=view
19            try{
20                filed.set(activity, view);
21            }catch (IllegalAccessException e)
22            {
23                e.printStackTrace();
24            }          
25        }
26    }
27}

1@Retention(RetentionPolicy.RUNTIME)
2@Target({ElementType.METHOD,ElementType.TYPE})
3@Inherited
4public @interface MyAnnotation {
5    //用于身份校验，默认为真
6    boolean CheckInfo() default true;
7}

 1@MyAnnotation
 2public class PeterOne {
 3    public void IAMSPIDERMAN(){
 4        System.out.println("我是第一代蜘蛛侠");
 5    }
 6}
 7
 8public class PeterThree extends PeterOne{
 9    public void IAMSPIDERMAN(){
10        System.out.println("我是第三代蜘蛛侠");
11    }
12}

 1public static void main(String[] args) {
 2   try {
 3       //获取child的Class对象
 4       PeterThree Holland = new PeterThree();//第三版的荷兰第蜘蛛侠
 5       Class clazz = Holland.getClass();
 6       //获取该对象IAMSPIDERMAN方法上CheckInfo类型的注解
 7       MyAnnotation myAnnotation = (MyAnnotation) clazz.getAnnotation(MyAnnotation.class);
 8       if (myAnnotation.CheckInfo()) {
 9           System.out.println("Yes，i am peter");
10       } else {
11           System.out.println("Yes，i am not peter");
12       }
13   } catch (Exception e) {
14       e.printStackTrace();
15   }
16}