TypeAnnoDemo.java

package chapter12;


//Demonstrate several type annotations
import java.lang.annotation.*;
import java.lang.reflect.*;

//A marker annotation that can be applied to a type
@Target(ElementType.TYPE_USE)
@interface TypeAnno{}

//Another marker annotation that can be applied to a type
@Target(ElementType.TYPE_USE)
@interface NotZeroLen{}

//Still another marker annotation that can be applied to a type
@Target(ElementType.TYPE_USE)
@interface Unique{}

//A parameterized annotation that can be applied to a type
@Target(ElementType.TYPE_USE)
@interface MaxLen{
    int value();
}

//An annotation that can be applied to a type parameter
@Target(ElementType.TYPE_PARAMETER)
@interface What2{
    String description();
}

//An annotation that can be applied to a field declaration
@Target(ElementType.FIELD)
@interface EmptyOk{}

//An annotation that can be applied to a method declaration
@Target(ElementType.METHOD)
@interface Recommended{}

//Use annotation on a type parameter
public class TypeAnnoDemo<@What2(description = "Generic data type") T> {

    //Use a type annotation on a constructor
    public @Unique TypeAnnoDemo(){}

    //Annotate the type (in this case string ),not the field
    @TypeAnno String str;

    //This annotates the field test
    @EmptyOk String test;

    //Use a type annotation to annotate this (the receiver)
    public int f(@TypeAnno TypeAnnoDemo<T> this,int x ){
        return 10;
    }

    //Annotate the return type
    public @TypeAnno Integer f2(int j,int k){
        return j+k;
    }

    //Annotate the method declaration
    public @Recommended Integer f3(String str){
        return str.length()/2;
    }

    //Use a type annotation with a throws clause
    public void f4() throws @TypeAnno NullPointerException{
        //...
    }

    //Annotate array levels
    String @MaxLen(10) [] @NotZeroLen [] w;

    //Annotate the array element type
    @TypeAnno Integer[] vec;

    public static void myMeth(int i){

        //Use a type annotation on a type argument
        TypeAnnoDemo<@TypeAnno Integer> ob=new TypeAnnoDemo<@TypeAnno Integer>();

        //Use a type annotation with new
        @Unique TypeAnnoDemo<Integer>ob2= new @Unique TypeAnnoDemo<Integer>();

        Object x = Integer.valueOf(10);
        Integer y;

        //Use type annotation on a cast
        y=(@TypeAnno Integer)x;


    }

    public static void main(String[] args) {
        myMeth(10);
    }
    //Use  type annotation with inheritance clause
    class SomeClass extends @TypeAnno TypeAnnoDemo<Boolean>{}
}