Package com.exonum.binding.storage.indices

Class EntryIndexProxy<T>

java.lang.Object

com.exonum.binding.proxy.AbstractNativeProxy

com.exonum.binding.storage.indices.EntryIndexProxy<T>

Type Parameters:

T - the type of an element in this entry

public final class EntryIndexProxy<T>
extends AbstractNativeProxy

An Entry is a database index that can contain no or a single value.

An Entry is analogous to Optional, but provides modifying ("destructive") operations when created with a Fork. Such methods are specified to throw UnsupportedOperationException if the entry is created with a Snapshot — a read-only database view.

All method arguments are non-null by default.

This class is not thread-safe and and its instances shall not be shared between threads.

When the view goes out of scope, this entry is destroyed. Subsequent use of the closed entry is prohibited and will result in IllegalStateException.

See Also:

View

Field Summary

Fields inherited from class com.exonum.binding.proxy.AbstractNativeProxy

nativeHandle

Method Summary

Modifier and Type	Method	Description
T	get()	If value is present in the entry, returns it, otherwise, throws NoSuchElementException.
String	getName()	Returns the name of this index.
boolean	isPresent()	Returns true if this entry exists in the database.
static <E> EntryIndexProxy<E>	newInstance(String name, View view, Serializer<E> serializer)	Creates a new Entry.
static <E extends com.google.protobuf.MessageLite> EntryIndexProxy<E>	newInstance(String name, View view, Class<E> elementType)	Creates a new Entry storing protobuf messages.
void	remove()	Removes a value from this entry.
void	set(T value)	Sets a new value of the entry, overwriting the previous value.
Optional<T>	toOptional()	Converts the entry to Optional.
String	toString()

Methods inherited from class com.exonum.binding.proxy.AbstractNativeProxy

getNativeHandle, isValidHandle

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Method Detail

newInstance

public static <E extends com.google.protobuf.MessageLite> EntryIndexProxy<E> newInstance(String name,
                                                                                         View view,
                                                                                         Class<E> elementType)

Creates a new Entry storing protobuf messages.

Type Parameters:

E - the type of entry; must be a protobuf message that has a static #parseFrom(byte[]) method

Parameters:

name - a unique alphanumeric non-empty identifier of the Entry in the underlying storage: [a-zA-Z0-9_]

view - a database view. Must be valid. If a view is read-only, "destructive" operations are not permitted.

elementType - the class of an element-protobuf message

Throws:

IllegalArgumentException - if the name is empty

IllegalStateException - if the view proxy is invalid

newInstance

public static <E> EntryIndexProxy<E> newInstance(String name,
                                                 View view,
                                                 Serializer<E> serializer)

Creates a new Entry.

Parameters:

name - a unique alphanumeric non-empty identifier of the Entry in the underlying storage: [a-zA-Z0-9_]

view - a database view. Must be valid. If a view is read-only, "destructive" operations are not permitted.

serializer - an entry serializer

Throws:

IllegalArgumentException - if the name is empty

IllegalStateException - if the view proxy is invalid

See Also:

StandardSerializers

set

public void set(T value)

Sets a new value of the entry, overwriting the previous value.

Parameters:

value - a value to set. Must not be null.

Throws:

UnsupportedOperationException - if the entry is read-only

IllegalStateException - if the proxy is invalid

isPresent

public boolean isPresent()

Returns true if this entry exists in the database.

Throws:

IllegalStateException - if the proxy is invalid.

get

public T get()

If value is present in the entry, returns it, otherwise, throws NoSuchElementException.

Returns:

a non-null value

Throws:

NoSuchElementException - if a value is not present in the Entry

IllegalStateException - if the proxy is invalid

IllegalArgumentException - if the supplied serializer cannot decode the value

remove

public void remove()

Removes a value from this entry.

Throws:

UnsupportedOperationException - if the entry is read-only.

IllegalStateException - if the proxy is invalid

toOptional

public Optional<T> toOptional()

Converts the entry to Optional.

Be aware that this method represents a state of the entry at the time of calling. And the returned value won't reflect the entry changes:

  
    entry.set("foo");
    Optional<String> optionalEntry = entry.toOptional();
    entry.remove();
    optionalEntry.get(); // -> returns "foo"
  
 

Returns:

Optional.of(value) if value is present in the entry, otherwise returns Optional.empty()

getName

public final String getName()

Returns the name of this index.

toString

public String toString()

Overrides:

toString in class Object