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1: /*
2:  * JOPA
3:  * Copyright (C) 2024 Czech Technical University in Prague
4:  *
5:  * This library is free software; you can redistribute it and/or
6:  * modify it under the terms of the GNU Lesser General Public
7:  * License as published by the Free Software Foundation; either
8:  * version 3.0 of the License, or (at your option) any later version.
9:  *
10:  * This library is distributed in the hope that it will be useful,
11:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
12:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13:  * Lesser General Public License for more details.
14:  *
15:  * You should have received a copy of the GNU Lesser General Public
16:  * License along with this library.
17:  */
18: package cz.cvut.kbss.jopa.proxy.lazy;
19: 
20: /**
21:  * Marker interface for lazy loading proxy implementations.
22:  *
23:  * @param <T> Type of the loaded value
24:  */
25: public interface LazyLoadingProxy<T> {
26: 
27:     /**
28:      * Triggers value loading.
29:      *
30:      * @return Loaded value
31:      */
32:     T triggerLazyLoading();
33: 
34:     /**
35:      * Checks whether this proxy has already been loaded.
36:      *
37:      * @return {@code true} if this proxy has been loaded, {@code false} otherwise
38:      */
39:     boolean isLoaded();
40: 
41:     /**
42:      * If this proxy has already been loaded, this method returns the loaded value.
43:      *
44:      * @return The loaded value, {@code null} if this proxy has not been loaded, yet
45:      * @see #isLoaded()
46:      * @throws IllegalStateException If called before this proxy is loaded
47:      */
48:     T getLoadedValue();
49: 
50:     /**
51:      * Gets a value that should be used to replace this proxy outside a persistence context.
52:      *
53:      * @return Default value to replace this proxy with
54:      */
55:     default T unwrap() {
56:         return null;
57:     }
58: }