src/java.base/share/classes/java/lang/invoke/SerializedLambda.java

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package java.lang.invoke;

import java.io.Serializable;
import java.io.InvalidObjectException;
import java.io.ObjectStreamException;
import java.lang.reflect.Method;
import java.util.Objects;

/**
 * Serialized form of a lambda expression.  The properties of this class
 * represent the information that is present at the lambda factory site, including
 * static metafactory arguments such as the identity of the primary functional
 * interface method and the identity of the implementation method, as well as
 * dynamic metafactory arguments such as values captured from the lexical scope
 * at the time of lambda capture.
 *
 * <p>Implementors of serializable lambdas, such as compilers or language
 * runtime libraries, are expected to ensure that instances deserialize properly.
 * One means to do so is to ensure that the {@code writeReplace} method returns
 * an instance of {@code SerializedLambda}, rather than allowing default
 * serialization to proceed.
 *
 * <p>{@code SerializedLambda} has a {@code readResolve} method that looks for
 * a (possibly private) static method called
 * {@code $deserializeLambda$(SerializedLambda)} in the capturing class, invokes
 * that with itself as the first argument, and returns the result.  Lambda classes
 * implementing {@code $deserializeLambda$} are responsible for validating
 * that the properties of the {@code SerializedLambda} are consistent with a
 * lambda actually captured by that class.
 *
 * <p>The identity of a function object produced by deserializing the serialized
 * form is unpredictable, and therefore identity-sensitive operations (such as
 * reference equality, object locking, and {@code System.identityHashCode()}) may
 * produce different results in different implementations, or even upon
 * different deserializations in the same implementation.
 *
 * @see LambdaMetafactory
 * @since 1.8
 */
public final class SerializedLambda implements Serializable {
    @java.io.Serial
    private static final long serialVersionUID = 8025925345765570181L;
    /**
     * @serial The capturing class.
     */
    private final Class<?> capturingClass;
    /**
     * @serial The functional interface class.
     */
    private final String functionalInterfaceClass;
    /**
     * @serial The functional interface method name.
     */
    private final String functionalInterfaceMethodName;
    /**
     * @serial The functional interface method signature.
     */
    private final String functionalInterfaceMethodSignature;
    /**
     * @serial The implementation class.
     */
    private final String implClass;
    /**
     * @serial The implementation method name.
     */
    private final String implMethodName;
    /**
     * @serial The implementation method signature.
     */
    private final String implMethodSignature;
    /**
     * @serial The implementation method kind.
     */
    private final int implMethodKind;
    /**
     * @serial The instantiated method type.
     */
    private final String instantiatedMethodType;
    /**
     * @serial The captured arguments.
     */
    @SuppressWarnings("serial") // Not statically typed as Serializable
    private final Object[] capturedArgs;

    /**
     * Create a {@code SerializedLambda} from the low-level information present
     * at the lambda factory site.
     *
     * @param capturingClass The class in which the lambda expression appears
     * @param functionalInterfaceClass Name, in slash-delimited form, of static
     *                                 type of the returned lambda object
     * @param functionalInterfaceMethodName Name of the functional interface
     *                                      method for the present at the
     *                                      lambda factory site
     * @param functionalInterfaceMethodSignature Signature of the functional
     *                                           interface method present at
     *                                           the lambda factory site
     * @param implMethodKind Method handle kind for the implementation method
     * @param implClass Name, in slash-delimited form, for the class holding
     *                  the implementation method
     * @param implMethodName Name of the implementation method
     * @param implMethodSignature Signature of the implementation method
     * @param instantiatedMethodType The signature of the primary functional
     *                               interface method after type variables
     *                               are substituted with their instantiation
     *                               from the capture site
     * @param capturedArgs The dynamic arguments to the lambda factory site,
     *                     which represent variables captured by
     *                     the lambda
     */
    public SerializedLambda(Class<?> capturingClass,
                            String functionalInterfaceClass,
                            String functionalInterfaceMethodName,
                            String functionalInterfaceMethodSignature,
                            int implMethodKind,
                            String implClass,
                            String implMethodName,
                            String implMethodSignature,
                            String instantiatedMethodType,
                            Object[] capturedArgs) {
        this.capturingClass = capturingClass;
        this.functionalInterfaceClass = functionalInterfaceClass;
        this.functionalInterfaceMethodName = functionalInterfaceMethodName;
        this.functionalInterfaceMethodSignature = functionalInterfaceMethodSignature;
        this.implMethodKind = implMethodKind;
        this.implClass = implClass;
        this.implMethodName = implMethodName;
        this.implMethodSignature = implMethodSignature;
        this.instantiatedMethodType = instantiatedMethodType;
        this.capturedArgs = Objects.requireNonNull(capturedArgs).clone();
    }

    /**
     * Get the name of the class that captured this lambda.
     * @return the name of the class that captured this lambda
     */
    public String getCapturingClass() {
        return capturingClass.getName().replace('.', '/');
    }

    /**
     * Get the name of the invoked type to which this
     * lambda has been converted
     * @return the name of the functional interface class to which
     * this lambda has been converted
     */
    public String getFunctionalInterfaceClass() {
        return functionalInterfaceClass;
    }

    /**
     * Get the name of the primary method for the functional interface
     * to which this lambda has been converted.
     * @return the name of the primary methods of the functional interface
     */
    public String getFunctionalInterfaceMethodName() {
        return functionalInterfaceMethodName;
    }

    /**
     * Get the signature of the primary method for the functional
     * interface to which this lambda has been converted.
     * @return the signature of the primary method of the functional
     * interface
     */
    public String getFunctionalInterfaceMethodSignature() {
        return functionalInterfaceMethodSignature;
    }

    /**
     * Get the name of the class containing the implementation
     * method.
     * @return the name of the class containing the implementation
     * method
     */
    public String getImplClass() {
        return implClass;
    }

    /**
     * Get the name of the implementation method.
     * @return the name of the implementation method
     */
    public String getImplMethodName() {
        return implMethodName;
    }

    /**
     * Get the signature of the implementation method.
     * @return the signature of the implementation method
     */
    public String getImplMethodSignature() {
        return implMethodSignature;
    }

    /**
     * Get the method handle kind (see {@link MethodHandleInfo}) of
     * the implementation method.
     * @return the method handle kind of the implementation method
     */
    public int getImplMethodKind() {
        return implMethodKind;
    }

    /**
     * Get the signature of the primary functional interface method
     * after type variables are substituted with their instantiation
     * from the capture site.
     * @return the signature of the primary functional interface method
     * after type variable processing
     */
    public final String getInstantiatedMethodType() {
        return instantiatedMethodType;
    }

    /**
     * Get the count of dynamic arguments to the lambda capture site.
     * @return the count of dynamic arguments to the lambda capture site
     */
    public int getCapturedArgCount() {
        return capturedArgs.length;
    }

    /**
     * Get a dynamic argument to the lambda capture site.
     * @param i the argument to capture
     * @return a dynamic argument to the lambda capture site
     */
    public Object getCapturedArg(int i) {
        return capturedArgs[i];
    }

    /**
     * Resolve a {@code SerializedLambda} to an object.
     * @return a SerializedLambda
     * @throws ObjectStreamException if the object is not valid
     */
    @java.io.Serial
    private Object readResolve() throws ObjectStreamException {
        try {
            Method deserialize = capturingClass.getDeclaredMethod("$deserializeLambda$", SerializedLambda.class);
            deserialize.setAccessible(true);
            return deserialize.invoke(null, this);
        } catch (ReflectiveOperationException roe) {
            throw new InvalidObjectException("ReflectiveOperationException during deserialization", roe);
        }
    }

    @Override
    public String toString() {
        String implKind=MethodHandleInfo.referenceKindToString(implMethodKind);
        return String.format("SerializedLambda[%s=%s, %s=%s.%s:%s, " +
                             "%s=%s %s.%s:%s, %s=%s, %s=%d]",
                             "capturingClass", capturingClass,
                             "functionalInterfaceMethod", functionalInterfaceClass,
                               functionalInterfaceMethodName,
                               functionalInterfaceMethodSignature,
                             "implementation",
                               implKind,
                               implClass, implMethodName, implMethodSignature,
                             "instantiatedMethodType", instantiatedMethodType,
                             "numCaptured", capturedArgs.length);
    }
}