LazyValue.java revision 12651:6ef01bd40ce2 
1/*
2 * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 */
23package org.graalvm.compiler.phases.common;
24
25import java.util.function.Supplier;
26
27/**
28 * A {@link Supplier} which always returns the same value, computed from an other supplier on the
29 * first access.
30 *
31 * <p>
32 * This implementation is not thread-safe and assumes the underlying supplier does not return null.
33 * If the underlying supplier returns null it will be called on each access until it returns a
34 * non-null value.
35 * </p>
36 */
37public class LazyValue<T> implements Supplier<T> {
38    private final Supplier<T> supplier;
39    private T value;
40
41    public LazyValue(Supplier<T> supplier) {
42        this.supplier = supplier;
43    }
44
45    @Override
46    public T get() {
47        if (value == null) {
48            value = supplier.get();
49        }
50        return value;
51    }
52}
53