In Java, a single element annotation is an annotation that has a single element, which is usually a value that is associated with the annotation. Single element annotations are also known as "value annotations" or "attribute annotations".

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

public class MyClass {
    @SuppressWarnings("unchecked")
    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 ("unchecked") parameter specifies the type of warning to suppress.

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

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

In this example, the @SuppressWarnings annotation is used to suppress all compiler warnings in the myMethod() method. Since no value is specified, the default value is used.

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

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Timeout {
    long value() default 1000;
}

In this example, the @Timeout annotation is defined with a single element value of type long. The value parameter is used to specify the timeout value in milliseconds, and it has a default value of 1000 if no value is specified. The @Retention and @Target annotations are used to specify that the @Timeout annotation can be applied to methods and should be retained at runtime.

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

@Timeout(5000)
public void myMethod() {
    // method body
}

In this example, the @Timeout annotation is used to specify a timeout value of 5000 milliseconds for the myMethod() method. If no value is specified, the default value of 1000 will be used.