NullPointerException demo

ManifestAnnotation.java

import java.lang.annotation.*;

public class ManifestAnnotation implements SampleAnnotation {

  private final String value;
  
  public ManifestAnnotation(String value) {
    this.value = value;
  }

  public Class<? extends Annotation> annotationType() {
    return ManifestAnnotation.class;
  }
  
  public String value() {
    return value;
  }
}

NullPointerSample.java

@SampleAnnotation
public class NullPointerSample {

  public static void main(String[] args) {
	System.out.println("-- hash code --");  // results in 0
	System.out.println(NullPointerSample.class.getAnnotation(SampleAnnotation.class).hashCode());
	
	System.out.println("-- to string --"); // ignores missing default value
	System.out.println(NullPointerSample.class.getAnnotation(SampleAnnotation.class).toString());
	
	System.out.println("-- equals --");  // throws NullPointerException, but should be false?
	System.out.println(NullPointerSample.class.getAnnotation(SampleAnnotation.class)
	    .equals(new ManifestAnnotation("bar")));
  }
}

SampleAnnotation.java

import java.lang.annotation.*;

@Retention(RetentionPolicy.RUNTIME)
public @interface SampleAnnotation {
  // NullPointerSample is compiled with default value of "foo".
  String value(); // default "foo";
}