Java Multiple element Annotations

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In Java, a multiple element annotation is an annotation that has more than one element, each of which can have a name and a value. Multiple element annotations are also known as "parameterized annotations" or "complex annotations".

Here's an example of a multiple element annotation in Java:

public class MyClass {
    @SuppressWarnings(value = "unchecked", justification = "legacy code")
    public void myMethod() {
        List myList = new ArrayList();
        // method body
    }
}

In this example, the @SuppressWarnings annotation is used to suppress compiler warnings for an unchecked cast operation in the myMethod() method. The value parameter specifies the type of warning to suppress, and the justification parameter provides a justification for why the warning is being suppressed.

Multiple element annotations can also have default values for their elements, which are used if no value is specified when the annotation is applied. Here's an example:

public class MyClass {
    @SuppressWarnings(value = "unchecked")
    public void myMethod() {
        List myList = new ArrayList();
        // method body
    }
}

In this example, the @SuppressWarnings annotation is used to suppress all unchecked warnings in the myMethod() method. Since only the value parameter is specified, the default value is used for the justification parameter.

You can define your own multiple element annotations in Java. Here's an example:

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Retry {
    int maxAttempts() default 3;
    long delay() default 1000;
    Class<? extends Exception>[] exceptions() default {};
}

In this example, the @Retry annotation is defined with three elements: maxAttempts, delay, and exceptions. The maxAttempts element is used to specify the maximum number of attempts to retry the method, the delay element is used to specify the delay between retries in milliseconds, and the exceptions element is used to specify the exceptions that should trigger a retry. All three elements have default values if no value is specified.

Here's an example of how you can use the @Retry annotation on a method:

@Retry(maxAttempts = 5, delay = 2000, exceptions = {IOException.class, TimeoutException.class})
public void myMethod() throws IOException, TimeoutException {
    // method body
}

In this example, the @Retry annotation is used to specify that the myMethod() method should be retried up to 5 times with a delay of 2 seconds between retries, and only if an IOException or TimeoutException is thrown. If no value is specified for an element, the default value will be used.