1 /* 2 * Copyright (C) 2007 The Guava Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.common.collect; 18 19 import static com.google.common.base.Preconditions.checkNotNull; 20 21 import com.google.common.annotations.GwtCompatible; 22 import com.google.common.base.Function; 23 import com.google.common.base.Objects; 24 25 import java.io.Serializable; 26 27 import javax.annotation.Nullable; 28 29 /** 30 * An ordering that orders elements by applying an order to the result of a 31 * function on those elements. 32 */ 33 @GwtCompatible(serializable = true) 34 final class ByFunctionOrdering<F, T> 35 extends Ordering<F> implements Serializable { 36 final Function<F, ? extends T> function; 37 final Ordering<T> ordering; 38 ByFunctionOrdering( Function<F, ? extends T> function, Ordering<T> ordering)39 ByFunctionOrdering( 40 Function<F, ? extends T> function, Ordering<T> ordering) { 41 this.function = checkNotNull(function); 42 this.ordering = checkNotNull(ordering); 43 } 44 compare(F left, F right)45 @Override public int compare(F left, F right) { 46 return ordering.compare(function.apply(left), function.apply(right)); 47 } 48 equals(@ullable Object object)49 @Override public boolean equals(@Nullable Object object) { 50 if (object == this) { 51 return true; 52 } 53 if (object instanceof ByFunctionOrdering) { 54 ByFunctionOrdering<?, ?> that = (ByFunctionOrdering<?, ?>) object; 55 return this.function.equals(that.function) 56 && this.ordering.equals(that.ordering); 57 } 58 return false; 59 } 60 hashCode()61 @Override public int hashCode() { 62 return Objects.hashCode(function, ordering); 63 } 64 toString()65 @Override public String toString() { 66 return ordering + ".onResultOf(" + function + ")"; 67 } 68 69 private static final long serialVersionUID = 0; 70 } 71