Graphic jdk1.8 new features (3) --- Notes and optimized type inference

Graphic jdk1.8 new features (3) --- Notes and optimized type inference

Get the same type more notes

jdk1.8 the java.lang.Classclass of the new method getAnnotationsByType, the method can obtain a list of one type of annotation, the specific code examples are as follows:

public class AnnotationTest {
    
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Filters {
        Filter[] value();
    }
    
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Repeatable(Filters.class)
    public @interface Filter {
        String value();
    }
    
    @Filter("filter1")
    @Filter("filter2")
    public interface Filterable {
        
    }
    
    @Filters({@Filter("filter1"), @Filter("filter2")})
    public interface Filterable2 {
        
    }
    
    public static void main(String[] args) {
        for (Filter filter : Filterable.class.getAnnotationsByType(Filter.class)) {
            System.out.println(filter.value());
        }
        for (Filters filter : Filterable.class.getAnnotationsByType(Filters.class)) {
            System.out.println(filter.value().length);
        }
        for (Filter filter : Filterable2.class.getAnnotationsByType(Filter.class)) {
            System.out.println(filter.value());
        }
        for (Filters filter : Filterable2.class.getAnnotationsByType(Filters.class)){
            System.out.println(filter.value().length);
        }
    }
}

输出如下：
filter1
filter2
2
filter1
filter2
2

---

Better type inference

​

The above can be seen that the getOrDefaultsecond parameter may be inferred by the first parameter, if before jdk1.8, to be written in the following form:

value.getOrDefault("asas", Value.<String>defaultValue());

---

Further expansion of annotations

• jdk1.8 extended context annotations, annotation is now added almost anywhere: local variables, generic class, and class implements ⽗ Connector, and even abnormal Remedies can also add annotations
• ElementType.TYPE_USE and ElementType.TYPE_PARAMETER are two newly added Use files described in the appropriate annotation type vertical element

---