tessl/maven-com-google-auto-value--auto-value
Generated immutable value classes for Java 8+ using annotation processing
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Pending
value-classes.mddocs/
Value Classes
AutoValue generates immutable value classes that automatically implement equals(), hashCode(), and toString() methods with proper value semantics. Value classes are defined as abstract classes with abstract property getter methods.
Basic Value Class
@AutoValue
public abstract class BasicExample {
public abstract String name();
public abstract int age();
public static BasicExample create(String name, int age) {
return new AutoValue_BasicExample(name, age);
}
}The generated class AutoValue_BasicExample will:
- Implement all abstract methods
- Provide proper equals() and hashCode() based on all properties
- Generate a readable toString() representation
- Be immutable (all fields are final)
Usage Example
BasicExample person = BasicExample.create("Alice", 30);
BasicExample samePerson = BasicExample.create("Alice", 30);
BasicExample differentPerson = BasicExample.create("Bob", 25);
System.out.println(person); // BasicExample{name=Alice, age=30}
System.out.println(person.equals(samePerson)); // true
System.out.println(person.equals(differentPerson)); // false
System.out.println(person.hashCode() == samePerson.hashCode()); // trueProperty Types
AutoValue supports all Java types as properties:
@AutoValue
public abstract class TypesExample {
// Primitives
public abstract int intValue();
public abstract long longValue();
public abstract boolean booleanValue();
public abstract double doubleValue();
// Object types
public abstract String stringValue();
public abstract List<String> listValue();
public abstract Optional<Integer> optionalValue();
// Custom types
public abstract CustomClass customValue();
// Arrays
public abstract String[] arrayValue();
public static TypesExample create(
int intValue,
long longValue,
boolean booleanValue,
double doubleValue,
String stringValue,
List<String> listValue,
Optional<Integer> optionalValue,
CustomClass customValue,
String[] arrayValue) {
return new AutoValue_TypesExample(
intValue, longValue, booleanValue, doubleValue,
stringValue, listValue, optionalValue, customValue, arrayValue);
}
}Nullable Properties
Properties can be marked as nullable using any annotation named "Nullable":
@AutoValue
public abstract class NullableExample {
@Nullable
public abstract String nullableProperty();
public abstract String requiredProperty();
public static NullableExample create(@Nullable String nullableProperty, String requiredProperty) {
return new AutoValue_NullableExample(nullableProperty, requiredProperty);
}
}Generic Value Classes
AutoValue supports generic type parameters:
@AutoValue
public abstract class GenericExample<T, U> {
public abstract T firstValue();
public abstract U secondValue();
public static <T, U> GenericExample<T, U> create(T firstValue, U secondValue) {
return new AutoValue_GenericExample<>(firstValue, secondValue);
}
}Inheritance and Interfaces
AutoValue classes can implement interfaces and extend abstract classes:
public interface Identifiable {
String getId();
}
@AutoValue
public abstract class IdentifiableEntity implements Identifiable {
@Override
public abstract String getId();
public abstract String name();
public static IdentifiableEntity create(String id, String name) {
return new AutoValue_IdentifiableEntity(id, name);
}
}Custom Methods
You can add custom methods to AutoValue classes:
@AutoValue
public abstract class PersonWithMethods {
public abstract String firstName();
public abstract String lastName();
public abstract int age();
// Custom method
public String fullName() {
return firstName() + " " + lastName();
}
// Custom predicate
public boolean isAdult() {
return age() >= 18;
}
public static PersonWithMethods create(String firstName, String lastName, int age) {
return new AutoValue_PersonWithMethods(firstName, lastName, age);
}
}Annotation Copying
Control which annotations are copied to the generated implementation:
@AutoValue
@CopyAnnotations // Copy class-level annotations
public abstract class AnnotatedExample {
@CopyAnnotations
@SuppressWarnings("example")
public abstract String annotatedProperty();
@CopyAnnotations(exclude = {Deprecated.class})
@Deprecated
@SuppressWarnings("example")
public abstract String selectivelyAnnotatedProperty();
public static AnnotatedExample create(String annotatedProperty, String selectivelyAnnotatedProperty) {
return new AutoValue_AnnotatedExample(annotatedProperty, selectivelyAnnotatedProperty);
}
}Validation
Add validation to factory methods:
@AutoValue
public abstract class ValidatedExample {
public abstract String email();
public abstract int age();
public static ValidatedExample create(String email, int age) {
checkArgument(email.contains("@"), "Invalid email: %s", email);
checkArgument(age >= 0, "Age must be non-negative: %s", age);
return new AutoValue_ValidatedExample(email, age);
}
private static void checkArgument(boolean condition, String message, Object... args) {
if (!condition) {
throw new IllegalArgumentException(String.format(message, args));
}
}
}Collection Properties
AutoValue works well with immutable collections:
@AutoValue
public abstract class CollectionExample {
public abstract ImmutableList<String> items();
public abstract ImmutableSet<Integer> values();
public abstract ImmutableMap<String, Object> properties();
public static CollectionExample create(
Iterable<String> items,
Iterable<Integer> values,
Map<String, Object> properties) {
return new AutoValue_CollectionExample(
ImmutableList.copyOf(items),
ImmutableSet.copyOf(values),
ImmutableMap.copyOf(properties));
}
}Error Handling
AutoValue generated constructors validate non-null parameters:
// This will throw NullPointerException
PersonExample person = PersonExample.create(null, 25); // NPE: name cannot be null
// Use Optional for nullable values instead
@AutoValue
public abstract class SafeExample {
public abstract Optional<String> optionalName();
public abstract int age();
public static SafeExample create(@Nullable String name, int age) {
return new AutoValue_SafeExample(Optional.ofNullable(name), age);
}
}Performance Considerations
- Generated equals() methods use efficient short-circuiting
- hashCode() is computed once and cached
- toString() builds strings efficiently
- All fields are final, enabling JVM optimizations
- No reflection is used at runtime
Install with Tessl CLI
npx tessl i tessl/maven-com-google-auto-value--auto-value