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  */
  23 package org.graalvm.compiler.phases.common;
  24 
  25 import 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  */
  37 public 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 }